FIELD

The present invention relates to luminescent materials and their heat treatment. The present invention also relates to a method for increasing intensity of optically simulated luminescence of such materials, and to a method for decreasing afterglow of such materials. The present invention still further relates to a method for increasing contrast of a computed radiography plate, the plate comprising the present material. Further, the invention relates to a method for increasing contrast of an image selected from computed radiography, computed tomography and digital radiography, the material used for imaging comprising the present material.

BACKGROUND AND OBJECTS

Hackmanite, which is a variety of sodalite material, is a natural mineral having the chemical formula of Na ₈ Al ₆ Si ₆ O ₂₄ (Cl,S) ₂ . A synthetic hackmanite-based material can be prepared and these materials can also be called hackmanites. These synthetic materials are described for example in WO 2017/194825 and WO 2017/194834, and can be used for various devices, such as for detecting and indicating the intensity of a radiation (as described in WO 2019/092309) or for determining the amount of radiation (as described in WO 2019/092308).

These materials are used also for example in computed radiography (CR). However, a problem with these types of materials is that their afterglow after optically stimulated luminescence (OSL) decreases the sharpness of the radiography images. It is thus an aim of the present disclosure to provide a method for decreasing this afterglow to increase sharpness of the images. A further aim is to increase the OSL intensity when the material is excited with a laser, again to increase the readability of the computed radiography images. In general, it is an aim of the present disclosure to improve readability (i.e. sharpness and intensity of signal) of computed radiography images and similar.

SUMMARY OF THE INVENTION

The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims. According to a first aspect, there is provided a method for heat treatment of a material represented by formula (I)

(M ^, ) ₈ (M ^{, ,} M ^{, , ,} ) ₆ O ₂₄ (X,X ^, ) ₂ :M”” formula (I) wherein

- M’ represents a monoatomic cation of an alkali metal selected from Group 1 of the IUPAC periodic table of the elements, or any combination of such cations;

- M” represents a trivalent monoatomic cation of an element selected from Group 13 of the IUPAC periodic table of the elements, or of a transition element selected from any of Groups 3 - 12 of the IUPAC periodic table of the elements, or any combination of such cations;

- M’” represents a monoatomic cation of an element selected from Group 14 of the IUPAC periodic table of the elements, or of an element selected from any of Groups 13 and 15 of the IUPAC periodic table of the elements, or of Zn, or any combination of such cations;

- X represents an anion of an element selected from Group 17 of the IUPAC periodic table of the elements, or any combination of such anions, or wherein X is absent;

- X’ represents an anion of one or more elements selected from Group 16 of the IUPAC periodic table of the elements, or any combination of such anions, or wherein X’ is absent; and

- M”” represents a dopant cation of an element selected from rare earth metals of the IUPAC periodic table of the elements, or from transition metals of the IUPAC periodic table of the elements, or of Ba, Sr, Tl, Pb, or Bi, or any combination of such cations, or wherein M”” is absent; with the proviso that at least one of X and X’ is present, and the heat treatment is carried out at a temperature of 250-900 °C, and for a period of time of 15-600 minutes.

According to a second aspect, there is provided a method for increasing intensity of optically simulated luminescence of a material represented by formula (I) as defined above, by carrying out the heat treatment described above. According to a third aspect, there is provided a method for decreasing afterglow of a material represented by formula (I) as defined above, by carrying out the heat treatment described above.

According to a fourth aspect, there is provided a method for increasing contrast of an image selected from computed radiography, computed tomography and digital radiography, by using a material represented by formula (I) as defined above, treated with the method as described below.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates the decrease of normal afterglow in heat-treated material of formula (I) according to one embodiment compared to non-treated material.

Figure 2 illustrates the decrease of normal afterglow in heat-treated material of formula (I) according to another embodiment compared to non-treated material.

Figure 3 illustrates the decrease of normal afterglow in heat-treated material of formula (I) according to a further embodiment compared to non-treated material.

Figure 4 illustrates the decrease of normal afterglow in heat-treated material of formula (I) according to an embodiment, in function of time of treatment.

Figure 5 illustrates the increase of intensity of optically stimulated luminescence in heat- treated material according to an embodiment.

Figure 6 illustrates the increase of intensity of optically stimulated luminescence in heat- treated material according to a further embodiment.

Figure 7 illustrates the effect of heat treatment and electron bombardment on the intensity of optically stimulated luminescence according to an embodiment.

Figure 8 illustrates the effect of an UV radiation on CR image, according to an embodiment.

Figure 9 illustrates the effect of an UV radiation on CR image, according to another embodiment.

Figure 10 illustrates ultraviolet enhancement of polymer emission for an embodiment. Figure 11 illustrates ultraviolet enhancement of polymer emission for another embodiment. Figure 12 illustrates ultraviolet enhancement of polymer emission for a further embodiment. DETAILED DESCRIPTION

The present description relates to a method for heat treatment of a material represented by formula (I)

(M ^, ) ₈ (M ^{, ,} M ^{, , ,} ) ₆ O ₂₄ (X,X ^, ) ₂ ^: M”” formula (I) wherein

- M’ represents a monoatomic cation of an alkali metal selected from Group 1 of the IUPAC periodic table of the elements, or any combination of such cations;

- M” represents a trivalent monoatomic cation of an element selected from Group 13 of the IUPAC periodic table of the elements, or of a transition element selected from any of Groups 3 - 12 of the IUPAC periodic table of the elements, or any combination of such cations;

- M’” represents a monoatomic cation of an element selected from Group 14 of the IUPAC periodic table of the elements, or of an element selected from any of Groups 13 and 15 of the IUPAC periodic table of the elements, or of Zn, or any combination of such cations;

- X represents an anion of an element selected from Group 17 of the IUPAC periodic table of the elements, or any combination of such anions, or wherein X is absent;

- X’ represents an anion of one or more elements selected from Group 16 of the IUPAC periodic table of the elements, or any combination of such anions, or wherein X’ is absent; and

- M”” represents a dopant cation of an element selected from rare earth metals of the IUPAC periodic table of the elements, or from transition metals of the IUPAC periodic table of the elements, or of Ba, Sr, Tl, Pb, or Bi, or any combination of such cations, or wherein M”” is absent; with the proviso that at least one of X and X’ is present, and the heat treatment is carried out at a temperature of 250-900 °C, and for a period of time of 15-600 minutes.

The material of formula (I) is an optically active material that is configured to be able to retain radiation such as X-radiation exposed thereon, i.e. the material is able to trap therein the radiation that it is exposed to, and to release the retained radiation as visible light when being subjected to optical stimulation, i.e. the retained radiation may be released from the optically active material later at a desired point of time.

The present description thus concerns the materials represented by formula (I), which are re-heated after their manufacture. Typically, the manufacturing process of these materials includes re-heating (as will be explained below), and therefore the present heat treatment is a further re-heating of the material. As will be demonstrated below in the Experimental part, the present heat treatment reduces the OSL afterglow of the materials, and increases the OSL signal intensity.

The heat treatment is carried out for a period of time. It is presently believed that as long as the temperature is not too high, there is no clear upper limit for the period of time useful for heating, but that after a certain period of time, further heating time does not have a noticeable effect on the material. The material is heated for a period of time of 15-600 minutes, such as for example from 15, 20, 25, 30, 45, 60, 90, 120, 150, 180, 210, 240, 270, 300, 330, 360, 390, 420, 450, 480, 510 or 540 minutes up to 30, 45, 60, 90, 120, 150, 180, 210, 240, 270, 300, 330, 360, 390, 420, 450, 480, 510, 540, 570 or 600 minutes.

The temperature used for the heat treatment is 250-900 °C, such as for example from 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 420, 440, 460,

480, 500, 520, 540, 560, 580, 600, 620, 640, 660, 680, 700, 720, 740, 760, 780, 800, 810,

820, 830, 840, 850, 860 or 870 °C, up to 280, 290, 300, 310, 320, 330, 340, 350, 360, 370,

380, 390, 400, 420, 440, 460, 480, 500, 520, 540, 560, 580, 600, 620, 640, 660, 680, 700,

720, 740, 760, 780, 800, 810, 820, 830, 840, 850, 860, 870, 880, 890 or 900 °C.

According to an embodiment, the heat treatment is carried out at a temperature of 400-600 °C, for example for 45-75 minutes. It is believed that this temperature range is especially suitable for increasing OSL intensity of at least certain materials according to formula (I). According to another embodiment, the heat treatment is carried out at a temperature of 400-700 °C, for example for 45-75 minutes. It is believed that this temperature range is especially suitable for decreasing the normal afterglow of at least certain materials according to formula (I). According to yet another embodiment, the upper temperature limit of the heat treatment is 850 °C.

The heat treatment is typically carried out in an oven. The material may be either gradually heated together with the oven, or it may be placed from room temperature to a ready- heated oven. In another embodiment, the material may pass through a series of ovens, having increasing temperatures. For example, the temperature difference between two consecutive ovens may be 50 or 100 °C. Also other types of devices can be used, such as chambers, furnaces etc.

According to an embodiment, the heat treatment is followed by cooling of the material in a step-wise manner. The material may for example be allowed to cool together with the oven, meaning that the cooling is gradual, i.e. the steps are small. The material may also be cooled by passing it through a series of ovens having decreasing temperatures. For example, the temperature difference between two consecutive ovens may be 50 or 100 °C. The cooling may also be carried out by removing the material from the hot oven to room temperature.

According to an embodiment, the heat treatment is carried out in an atmosphere of air, nitrogen, argon, oxygen or mixtures thereof. A reducing gas may also be used during the heat treatment.

In one embodiment, M’ represents a monoatomic cation of an alkali metal selected from a group consisting of Na, Li, K, Rb, Cs, and Fr, or any combination of such cations. In another embodiment, M’ represents a monoatomic cation of an alkali metal selected from Group 1 of the IUPAC periodic table of the elements, or any combination of such cations, with the proviso that M’ does not represent the monoatomic cation of Na alone. According to an embodiment, M’ represents a combination of at least two monoatomic cations of different alkali metals selected from a group consisting of Li, Na, K, Rb, Cs, and Fr.

In one embodiment, M’ represents a combination of at least two monoatomic cations of different alkali metals selected from Group 1 of the IUPAC periodic table of the elements. In one embodiment, M’ represents a combination of at least two monoatomic cations of different alkali metals selected from Group 1 of the IUPAC periodic table of the elements, wherein the combination comprises at most 98 mol-%, at most 95 mol-%, at most 90 mol- %, at most 85 mol-%, at most 80 mol-%, at most 70 mol-%, at most 60 mol-%, at most 50 mol-%, at most 40 mol-% of the monoatomic cation of Na, or at most 30 mol-% of the monoatomic cation of Na, or at most 20 mol-% of the monoatomic cation of Na.

In a yet further embodiment, M’ represents a monoatomic cation of Li. In one embodiment, M’ represents a monoatomic cation of K. In one embodiment, M’ represents a monoatomic cation of Rb. In one embodiment, M’ represents a monoatomic cation of Cs. In one embodiment, M’ represents a monoatomic cation of Fr.

In one embodiment, M” represents a trivalent monoatomic cation of a metal selected from a group consisting of A1 and Ga, or a combination of such cations. In one embodiment, M” represents a trivalent monoatomic cation of B. In one embodiment, M” represents a trivalent monoatomic cation of a transition element selected from Period 4 of the IUPAC periodic table of the elements, or any combination of such cations. In one embodiment, M” represents a trivalent monoatomic cation of an element selected from a group consisting of Cr, Mn, Fe, Co, Ni, and Zn, or any combination of such cations.

In one embodiment, M’” represents a monoatomic cation of an element selected from a group consisting of Si, Ge, Al, Ga, N, P, and As, or any combination of such cations. In one embodiment, M’” represents a monoatomic cation of an element selected from a group consisting of Si and Ge, or a combination of such cations. In one embodiment, M’” represents a monoatomic cation of an element selected from a group consisting of Al, Ga, N, P, and As, or any combination of such cations. In one embodiment, M’” represents a monoatomic cation of an element selected from a group consisting of Al and Ga, or a combination of such cations. In one embodiment, M’” represents a monoatomic cation of an element selected from a group consisting of N, P, and As, or any combination of such cations. In one embodiment, M’” represents a monoatomic cation of Zn.

In one embodiment, X represents an anion of an element selected from a group consisting of F, Cl, Br, I, and At, or any combination of such anions. In one embodiment, X represents an anion of an element selected from a group consisting of F, Cl, Br, and I, or any combination of such anions. In one embodiment, X is absent.

In one embodiment, X’ represents an anion of an element selected from a group consisting of O, S, Se, and Te, or any combination of such anions. In one embodiment, X’ represents an anion of one or more elements selected from a group consisting of O, S, Se, and Te, or any combination of such anions. In one embodiment, X’ represents a monoatomic or a polyatomic anion of one or more elements selected from a group consisting of O, S, Se, and Te, or any combination of such anions. In one embodiment, X’ represents an anion of

S. In an embodiment, X’ In yet another embodiment X’ is absent. The proviso that at least one of X and X’ is present should in this specification, unless otherwise stated, be understood such that either X or X’ is present, or such that both X and X’ are present.

In one embodiment, the material is doped with at least one transition metal ion.

In one embodiment, the material is represented by formula (I), wherein M”” represents a cation of an element selected from transition metals of the IUPAC periodic table of the elements, or of Ba, Sr, Tl, Pb, or Bi, or any combination of such cations. In one embodiment, M”” represents a cation of an element selected from transition metals of the f-block of the IUPAC periodic table of the elements. In one embodiment, M”” represents a cation of an element selected from transition metals of the d-block of the IUPAC periodic table of the elements. In one embodiment, M”” represents a cation of an element selected from a group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Ag, W, and Zn, or any combination of such cations. In one embodiment, M”” represents a cation of Ti. In one embodiment, M”” represents a dopant cation of an element selected from rare earth metals of the IUPAC periodic table of the elements. In one embodiment, M”” represents a cation of an element selected from a group consisting of Yb, Er, Tb, and Eu, or any combination of such cations. In one embodiment, M”” represents a combination of two or more dopant cations.

In one embodiment, the material is represented by formula (I), wherein M”” is absent. In this embodiment, the material is not doped. In one embodiment, the material represented by the formula (I) comprises M”” in an amount of 0.001 - 10 mol-%, or 0.001 - 5 mol-%, or 0.1 - 5 mol-% based on the total amount of the material.

According to a further embodiment, the material represented by formula (I) comprises residuals. These residuals originate from the manufacturing process of the material, and may be present in an amount of up to 1 mol-% or even more, such as up to 10 mol-%.

In one embodiment, the material represented by formula (I) is selected from a group consisting of:

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Ga) ₆ Si ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Cr) ₆ Si ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Mn) ₆ Si ₆ O ₂₄ (Cl,S) ₂ :Ti, (Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Fe) ₆ Si ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Co) ₆ Si ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Ni) ₆ Si ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Cu) ₆ Si ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,B) ₆ Si ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Mn ₆ Si ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Cr ₆ Si ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Fe ₆ Si ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Co ₆ Si ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Ni ₆ Si ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Cu ₆ Si ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ B ₆ Si ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Ga ₆ Si ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Al ₆ Si ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Al ₆ (Si,Zn) ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Al ₆ (Si,Ge) ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Al ₆ (Zn ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Al ₆ (Ge ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Al ₆ (Ga,Si,N) ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Al ₆ (Ga,Si,As) ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Al ₆ (Ga,N) ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Al ₆ (Ga,As) ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Ga) ₆ Ge ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Cr) ₆ Ge ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Mn) ₆ Ge ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Fe) ₆ Ge ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Co) ₆ Ge ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Ni) ₆ Ge ₆ O ₂₄ (Cl,S) ₂ :Ti, (Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Cu) ₆ Ge ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,B) ₆ Ge ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Mn ₆ Ge ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Cr ₆ Ge ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Fe ₆ Ge ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Co ₆ Ge ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Ni ₆ Ge ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Cu ₆ Ge ₆ O ₂₄ (Cl,S) ₂ :Ti,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ B ₆ Ge ₆ O ₂₄ (Cl,S) ₂ :Ti, and

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Ga ₆ Ge ₆ O ₂₄ (Cl,S) ₂ :Ti, wherein x + y + z < 1 , and x ³ 0, y > 0, z > 0.

Some further suitable materials are LiNa ₇ Al ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr, where the amount of Sr varies from 3 to 6 mol-%. The material may also comprise Cu, for example in the amount of 1 mol-%. Some suitable materials represented by formula (I) can be selected from a group consisting of:

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Ga) ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Cr) ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Mn) ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Fe) ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Co) ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Ni) ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Cu) ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,B) ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Mn ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Cr ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Fe ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Co ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr, (Li _x Na _1-x-y-z K _y Rb _z ) ₈ Ni ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Cu ₆ Si ₆ O24(Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ B ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Ga ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Al ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Al ₆ (Si,Zn) ₆ O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Al ₆ (Si,Ge) ₆ O ₂₄ (Br,S) ₂ :Sr,

( ^Li x ^Na l-x-y-z ^K y ^Rb z)8 ^A1 6 ^Zn 6O ₂₄ (Br,S) ₂ :Sr,

( ^Li x ^Na l-x-y-z ^K y ^Rb z)8 ^A1 6 ^Ge 6O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Al ₆ (Ga,Si,N) ₆ O ₂₄ (Br,S) ₂ : Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Al ₆ (Ga,Si,As) ₆ O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Al ₆ (Ga,N) ₆ O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Al ₆ (Ga,As) ₆ O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Ga) ₆ Ge ₆ O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈₍ Al,Cr) ₆ Ge ₆ O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Mn) ₆ Ge ₆ O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Fe) ₆ Ge ₆ O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Co) ₆ Ge ₆ O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Ni) ₆ Ge ₆ O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Cu) ₆ Ge ₆ O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,B) ₆ Ge ₆ O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Mn ₆ Ge ₆ O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Cr ₆ Ge ₆ O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Fe ₆ Ge ₆ O ₂₄ (Br,S) ₂ .Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Co ₆ Ge ₆ O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Ni ₆ Ge ₆ O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Cu ₆ Ge ₆ O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ B ₆ Ge ₆ O ₂₄ (Br,S) ₂ :Sr, (Li _x Na _1-x-y-z K _y Rb _z ) ₈ Ga ₆ Ge ₆ O ₂₄ (Br,S) ₂ :Sr,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Ga) ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Cr) ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Mn) ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Fe) ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Co) ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Ni) ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Cu) ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,B) ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Mn ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Cr ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Fe ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Co ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Ni ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Cu ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ B ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Ga ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Al ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Al ₆ (Si,Zn) ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Al ₆ (Si,Ge) ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Al ₆ Zn ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Al ₆ Ge ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Al ₆ (Ga,Si,N) ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Al ₆ (Ga,Si,As) ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Al ₆ (Ga,N) ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Al ₆ (Ga,As) ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Ga) ₆ Ge ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈₍ Al,Cr) ₆ Ge ₆ O ₂₄ (Br,S) ₂ :Sr,Cu, (Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Mn) ₆ Ge ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Fe) ₆ Ge ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Co) ₆ Ge ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Ni) ₆ Ge ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,Cu) ₆ Ge ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ (Al,B) ₆ Ge ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Mn ₆ Ge ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Cr ₆ Ge ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Fe ₆ Ge ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Co ₆ Ge ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Ni ₆ Ge ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Cu ₆ Ge ₆ O ₂₄ (Br,S) ₂ :Sr,Cu,

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ B ₆ Ge ₆ O ₂₄ (Br,S) ₂ :Sr,Cu, and

(Li _x Na _1-x-y-z K _y Rb _z ) ₈ Ga ₆ Ge ₆ O ₂₄ (Br,S) ₂ :Sr,Cu, wherein x + y + z < 1 , and x ≥ 0, y ≥ 0, z ≥ 0.

The material may be synthesized by a reaction according to Norrbo et al. (Norrbo, I.; Głuchowski, P.; Paturi, P.; Sinkkonen, J.; Lastusaari, M., Persistent Luminescence of TenebrescentNa ₈ Al ₆ Si ₆ O ₂₄ (Cl,S) ₂ : Multifunctional Optical Markers. Inorg. Chem. 2015,

54, 7717-7724), which reference is based on Armstrong & Weller (Armstrong, J.A.; Weller, J.A. Structural Observation of Photochromism. Chem. Commun. 2006, 1094- 1096). As an example, stoichiometric amounts of Zeolite A and Na ₂ S04 as well as LiCl,

NaCl, KC1 and/or RbCl can be used as the starting materials. The at least one dopant may be added as an oxide, such as Ti0 ₂ , a chloride, a sulfide, a bromide, or a nitrate. The material can be prepared as follows: Zeolite A may first be dried at 500 °C for 1 h. The initial mixture may then be heated at 850 °C in air for e.g. 2 h, 5 h, 12 h, 24 h, 36 h, 48 h, or 72 h. The product may then be freely cooled down to room temperature and ground. Finally, the product may be re-heated at 850 °C for 2 h under a flowing 12 % H ₂ + 88 % N ₂ atmosphere. If needed, the as-prepared materials may be washed with water to remove any excess LiCl/NaCl/KCl/RbCl impurities. The purity can be verified with an X-ray powder diffraction measurement.

The material is prepared in powder form, and is typically also used in powder form. The particle size in the powder is typically about 5-10 pm, as measured by transmission electron microscopy, the area was determined from the pictures with a watershed segmentation algorithm in the ImageJ program.

According to an alternative embodiment, the material treated has formula (II) (M ^, ) ₈ (M”M’”) ₆ O ₂₄ (X,S) ₂ :M”” formula (II) wherein

- M’ represents a monoatomic cation of an alkali metal selected from Group 1 of the IUPAC periodic table of the elements, or any combination of such cations;

- M” represents a trivalent monoatomic cation of an element selected from Group 13 of the IUPAC periodic table of the elements, or of a transition element selected from any of Groups 3 - 12 of the IUPAC periodic table of the elements, or any combination of such cations;

- M’” represents a monoatomic cation of an element selected from Group 14 of the IUPAC periodic table of the elements, or any combination of such cations;

- X represents an anion of an element selected from Group 16 of the IUPAC periodic table of the elements, or from Group 17 of the IUPAC periodic table of the elements, or any combination of such anions; and

- M”” represents a dopant cation of an element selected from rare earth metals of the IUPAC periodic table of the elements, or from transition metals of the IUPAC periodic table of the elements, or any combination of such cations, or wherein M”” is absent.

The various embodiments and options for the different constituents of the material according to formula (I) listed above apply mutatis mutandis to materials according to formula (II).

The material of the present description is typically non-toxic and non-expensive and also has the benefit of being reusable and recyclable. The present description also relates to the present method of heat treatment, followed by treating the heat treated material with electron bombardment. According to another embodiment, the heat treatment can be carried out on a material that has been electron bombarded as explained below.

Electron bombardment is a generally known ionization method in which electrons interact with solid or gas phase atoms or molecules to produce ions. Ionization by electron bombardment uses highly energetic electrons to produce ions, which leads to extensive fragmentation. Electron bombardment is non-selective ionization method which provides high ionization efficiency and sensitivity.

The material is preferably treated with the electron bombardment in powder form. Typically, the powder sample is spread as a thin surface onto a sample holder which is then put into a vacuum. In the chamber, the sample is being bombarded, typically small area at a time until the whole sample surface has been treated. The apparatuses for carrying out electron bombardment are known as such.

The electron bombardment of material having the formula (I) is carried out in a vacuum chamber having a pressure enabling formation of an electron beam. For some typical equipment, this means a pressure of at most 15 Pa. According to another embodiment, the vacuum chamber has a pressure of at most 10 Pa, for example at most 5 Pa. The vacuum chamber can for example have a pressure of 1, 3, 5, 7, 10 or 12 Pa up to 3, 5, 7, 10, 12 or 15 Pa.

According to one embodiment, the electron bombardment is carried out using a voltage of 0.1-50 kV. For example, the voltage can be from 0.1, 1, 5, 8, 10, 12, 15, 18, 20, 22, 25, 28, 30, 32, 35, 37, 40, 42, 45 or 47 kV up to 1, 5, 8, 10, 12, 15, 18, 20, 22, 25, 28, 30, 32, 35, 37, 40, 42, 45, 47 or 50 kV.

According to another embodiment, the electron bombardment is carried our using a current of 0.01-0.5 mA. For example, the current can be from 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4 or 0.45 mA up to 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45 or 0.5 mA.

The electron bombardment is carried out for a period of time. The time used for electron bombardment is typically selected based on the other process parameters. According to one embodiment, the material is exposed to the electron bombardment for a time period of 1 to 40 minutes. In other embodiments, the time could be even less than one minute or more than 40 minutes, such as 45 minutes or an hour. For example, the time can be from 1, 2, 3, 4, 6, 9,10, 15, 20, 25 or 30 minutes up to 2, 3, 4, 6, 9, 10, 15, 20, 25, 30, 35 or 40 minutes.

According to another embodiment, the heat treated or the heat treated and electron bombarded material is further arranged in a polymer matrix. The thus obtained product is thereafter treated with ultraviolet (UV) irradiation.

It has been surprisingly found that ultraviolet irradiation treatment can be used to further improve optical properties of the material of formula (I). Ultraviolet irradiation treatment enables increasing luminescence and optically stimulated luminescence intensity in computed radiography (CR) imaging, in digital radiography (DR) imaging and computed tomography (CT) imaging. The imaging techniques may use plates or detectors, or a combination of plates and detectors. The detectors may be for example X-ray detectors. In order to obtain the beneficial effect of ultraviolet irradiation, the material of formula (I) is believed to require being arranged in a polymer matrix.

Without wishing to be bound by a theory, it seems that the polymer matrix acts as an energy converter that absorbs ultraviolet emission from the material, converts it to such wavelengths that can be read by CR plate reader and emits it to the reader. Thus, ultraviolet treatment makes more of the optically stimulated luminescence of the material of formula (I) visible to the CR plate reader, i.e. converts especially the high-energy part of the optically stimulated luminescence into wavelengths that CR reader can see (blue light). Ultraviolet radiation enhances the blue emission of the polymer by widening the excitation band of the polymer. Thus, the CR image becomes brighter and/or higher in contrast. Thus, ultraviolet irradiation treatment of the material arranged in polymer matrix results in increased optically stimulated luminescence signal. It has been noted that the ultraviolet treatment does not seem to affect the material as such, but only the polymer matrix, especially the surface of the polymer matrix.

According to one embodiment, the material can be arranged in a polymer matrix by using tape casting, also known as knife coating or doctor blading. Tape casting is a process where a thin sheet of ceramic or metal particle suspension fluid is cast on a substrate. The fluid may contain volatile nonaqueous solvents, a dispersant, (a) binder(s) and the dry matter, i.e. the material having formula (I). The process may comprise preparing the suspension and applying it onto a surface of a substrate. The binder may create a polymer network around the dry matter particles, while the plasticizer may function as a softening agent for the binder. When combining these substances, the tape may become resistant against cracking and flaking off when bent. The dispersant may be used to de-aggregate the particles and homogenize the suspension.

Thus, according to one embodiment the material is arranged in a polymer matrix by mixing the material with the tape casting components. Any suitable and typical tape casting components can be used, as known in the art. According to one embodiment, the tape casting components comprise ethanol Aa, ethyl methyl ketone, triton X-100, benzyl butyl phthalate and polyvinyl butyral.

The polymer matrix, i.e. tape-casting polymer, can comprise one or several different polymers. Any polymer capable to act as an energy converter, i.e. capable to be excited by the optically stimulated luminescence emission, can be used. According to one embodiment, the polymer can be benzyl butyl phthalate or polyvinyl butyral or any combination thereof.

The material, tape-casted in a polymer matrix, forms an image detector that can be used in computed radiography imaging after the beneficial UV treatment.

According to one embodiment the ultraviolet irradiation is made using an irradiation with wavelength of 200 to 310 nm. The exposure time for the UV irradiation is for example 10 seconds to 30 minutes. The time can thus be for example from 10, 15, 30 or 45 seconds or from 1, 5, 10 or 20 minutes up to 15, 30 or 45 seconds or 1, 5, 10, 20, 25 or 30 minutes.

According to one embodiment the ultraviolet irradiation intensity used is 4 to 6 mW/cm ² . Thus, ultraviolet irradiation treatment can be performed for example with wavelength of

302 nm and intensity of 4.25mW/cm ² or with wavelength of 254 nm and intensity of 5.92 mW/cm ² .

The present materials may be used in X-ray imaging, in computed radiography (CR) imaging, in digital radiography (DR) imaging and in computed tomography (CT) imaging. The imaging techniques may use plates or detectors, or a combination of plates and detectors. The detectors may be for example X-ray detectors. These plates and detectors may comprise the present material that has been treated, or the plate or detector (also called in general image detectors) may first be formed and thereafter the material may be treated as discussed. The material according to formula (I) may be attached to a surface for example as a coating or a film. The substrate of the plate or detector may comprise or consist of glass or polymer. The substrate may comprise or consist of a glass layer or a polymer layer. The substrate may comprise (a) further layer(s). The substrate may also or alternatively comprise an attachment layer, such as a printing paper, and/or a base layer, such as a cardboard layer, or any other layer(s) where desired or needed. The image detector may comprise further layers and/or components. The image detector has the added utility of enabling the use of the material represented by formula (I) as a detector material for imaging purposes. The image detector has a further added utility of making use of an optically active material being non-toxic and non-expensive compared to currently used materials such as Ba(F,Cl,Br,I) ₂ :Eu and CsTTi. The image detector has still an added utility of being reusable and recyclable. Further, the image detector can be used for point- of-care analysis without the need of complicated analysis systems.

The present description further relates to a device, wherein the device comprises a material according to one or more embodiments described in this specification. In one embodiment, the device is an ultraviolet radiation sensor, an ultraviolet radiation detector, or an ultraviolet radiation indicator. In one embodiment, the device is an X-radiation sensor, an X-radiation detector, an X-radiation indicator, or an X-radiation dose indicator.

The present method of heat treatment of the material has the effect of increasing intensity of optically simulated luminescence. The present description thus relates also to a method for increasing intensity of optically simulated luminescence of a material represented by formula (I) as defined above, by carrying out the heat treatment as described also above. This effect is obtained especially when the material is both heat treated and electron bombarded.

A further effect of the present heat treatment is the decrease of afterglow of the present materials. Thus, the present description also relates to a method for decreasing afterglow of a material represented by formula (I) as defined above, by carrying out the heat treatment described above. According to an embodiment, the decreased afterglow is afterglow of optically stimulated luminescence, the optical stimulation being carried out with laser. This effect is obtained especially when the material is both heat treated and electron bombarded. In this specification, unless otherwise stated, the expressions "afterglow", "persistent lumi- nescense", "phosphorescence", or any corresponding expression should be understood as referring to the phenomenon encountered in materials which make them glow in the dark after having been excited with ultraviolet or visible light or with higher energy radiation.

A still further aspect of this description is a method for increasing contrast of a computed radiography plate, by using a material represented by formula (I) and treated with ultraviolet (UV) irradiation, as explained above.

It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention.

The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", i.e. a singular form, throughout this document does not exclude a plurality.

In the following Experimental part, concrete examples of the heat treatment are given to further illustrate the invention. Some examples of UV irradiation are also given.

EXPERIMENTAL PART

Example 1 - Preparation of the materials

The materials tested had the formula LiNa ₇ Al ₆ Si ₆ O ₂₄ (Br,S) ₂ :Sr, with various amounts of Sr. One sample also had some Cu. The amounts of Sr (and Cu) are given below in Table 1. During the synthesis of the materials, zeolite A was first dried at 500 °C for 1 h. Stoichiometric amounts of zeolite A, NaBr, Na ₂ SO ₄ and LiBr were used as the starting materials. The dopants were added as bromides (SrBr ₂ , CuBr when used). The following conditions were used: - for the materials MT13, MT24, MT80 and MT82: first heating was carried out at 800

°C in air for 5 hours, then a second heating at 850 °C under an atmosphere of 12 vol-% H ₂ and 88 vol-% N ₂ for 2 hours; for the material MT43: first heating was carried out at 795 °C in air for 5 hours, then a second heating at 850 °C under an atmosphere of 12 % H ₂ and 88 % N ₂ for 2 hours. Example 2 - Heat treatment

The material was heat treated as described below. The below explained heat-treatment was thus a third heating of the material, since the beginning of its manufacturing.

A small amount of each material (approximately 5-10 mg) was placed into a small thermogravimetric analysis crucible. Each sample was then heated in a Nabertherm N3/C8 muffle furnace at the default heating rate of approximately 20 °C/min up to a certain temperature (which varied between 200 and 850 °C, see table below) in air at normal pressure (1 atm). The sample was kept for 1 h or 2 h at the desired temperature before being allowed to cool freely inside the furnace. Once the sample had cooled down, it was collected and its optically stimulated luminescence (OSL) and the normal afterglow after excitation at 254 nm were measured (as explained in more detail below).

For each material, the MTxxa is the reference material that was not heat-treated, while the MTxxb-j is the heat-treated sample.

Table 1 Example 3 - UV irradiation treatment

The materials used were as indicated in Table 2.

Table 2

Example 3 a The materials MT55 and MT57 were each suspended separately in a tape-cast polymer matrix comprising ethanol Aa (15 weight-%), ethyl methyl ketone (= 2-butanone, 30 weight-%), 2-[4-(2,4,4-trimethylpentan-2-yl)phenoxy]ethanol (sold under tradename Triton X-100, 2 weight-%), benzyl butyl phthalate (BBP, 6 weight-%) and polyvinyl butyral (PVB, 7 weight-%), the amount of MT55 or MT57 being 40 weight-%. The mixture was then cast onto a polyester projector transparency, and subjected to UV irradiation at 20 °C and normal air pressure (1 atm). A 302 nm handheld UVP model UVM-57, 6 W lamp was placed directly on top of the sample and switched on, exposing the sample to UV radiation for 5-30 min with an irradiance of 4.25 mW/cm^. When the photochromism of the material had faded, the enhanced glow of the polymer was visible under 302 nm and 365 nm UV light.

Example 3b

The material of formula Na ₈ Al ₆ Si ₆ O ₂₄ (Cl,S) ₂ was suspended in the same polymer matrix as in Example 3a and subjected to 254 nm UV irradiation from a handheld UVP model UVLS-24 EL, 4 W 254/365 nm lamp, also at 20 °C and normal air pressure (1 atm). The lamp was placed directly on top of the sample and switched on, exposing the sample to UV radiation for between 10 seconds and 30 minutes with an irradiance of 5.92 mW/cm ² . When the photochromism of the material had faded, the enhanced glow of the polymer was visible under 302 nm and 365 nm UV light. Example 3 c

The tape-cast polymer as well as the polyester projector transparency of Example 3a (i.e. without any material according to formula (I)) were exposed to UV irradiation by the same 302 nm lamp for 25 minutes at an irradiance of 4.25 mW/cm^. After irradiation ceased, the enhanced glow of the polymers was visible immediately under 302 nm and 365 nm UV light.

Example 4 - Electron bombardment treatment

The heat-treated sample MT82b was also electron bombarded. The temperature and pressure in the laboratory was kept at 20 °C and 1 atm. Approximately 30 mg of sample powder was spread as a thin surface onto a glass sample holder which was then put into the vacuum chamber Nuclide Corp. ELM2B connected to a Franklin Electric model 1102685400 vacuum pump providing continuous suction. The control unit Nuclide Corp. ELM2EX was then used to control the voltage and current levels for the electron bombardment. The voltage was kept at 8.75-10.0 kV and the current was kept at 0.74-0.80 mA. When the equipment's pressure reading was 6.13-6.53 Pa, the electron beam was visible and could be visually adjusted with magnets that were held on both sides of the vacuum chamber's window. In these experiments, the visible beam was kept oval shaped, measuring 7 mm x 30 mm. This area of the sample was bombarded for 20 min, after which a new, unexposed area was bombarded for the same time until the whole surface of the sample surface had been exposed to a same current, voltage and time product.

Optically stimulated luminescence (OSL) measurements

OSL intensity and afterglow were measured as follows. The temperature and pressure in the laboratory were kept at 20 °C and 1 atm. First, the sample powder was put into a glass capillary tube measuring 75 x 2.0 mm (Marienfeld no. 29 402 02). The sample was then irradiated with a Hg discharge lamp providing 254 nm emission and put at a distance where the irradiance was 0.12 mW/cm^. The sample tube was spun at a rate of 70 revolutions per second and is irradiated for 60 s while spinning. The sample tube was then put into the middle of a measuring chamber with a 44.4 mm inner diameter and kept there for either 5 hours (MT82 in Figure 7) or 12 hours (MT 80 and MT82 in Figures 5 and 6)to eliminate the initial afterglow. The OSF intensity was measured by irradiating the sample with a 635 nm laser supplying 96 mA power output for 0.1 s. One measurement set was an average of 100 measurements with 1.0 s scan time per measurement or an average of 10 measurements with 10.0 s scan time per measurement using a sampling step of 1 ms or 10 ms, respectively (10 measurements with 10.0 s scan time per measurement using 10 ms sampling step for MT80 and MT82 in Figures 5 and 6; 100 measurements with 1.0 s scan time per measurement using 1 ms sampling step for MT82 in Figure 7).

The adjustment of the laser beam was carried out with a 600 nm long wave pass filter, and the emission side consists of Thorlabs LA1951-B F25.4 mm lens, short wave pass filter 550 nm, short wave pass filter 600 nm, Thorlabs LA1951-B F25.4 mm lens, and finally a photomultiplier tube, respectively. The photomultiplier tube was connected to a Stanford Research Systems SR570 low noise current preamplifier (parameters: bias voltage POS, filter type: none, input offset: 1 pA, gain mode: low noise, sensitivity: 20 or 50 nA/V; (20 nA/V used for MT80 and MT82 in Figures 5 and 6; 50 nA/V used for MT82 in Figure 7) and to a Stanford Research Systems PS325 high voltage power supply unit. The preamplifier was connected to ports 7 and 8 in a National Instruments NI USB-6251 multifunction I/O device. A wire loop from ports 4 and 5 to ports 15 and 16 was connected in parallel to a Tektronic TDS 420 oscilloscope and a Newport laser diode driver model 5060. The laser diode driver was connected to a Thorlabs LDM9LD laser diode, which was connected to a TE Technology TL-48-20 temperature control unit. The temperature of the laser diode was kept at 18.0 °C and controlled with a Wentronic DF17132SB DL PSV laboratory power supply set to 2.8 V.

Normal afterglow measurement

The normal afterglow was measured with a luminance spectrometer setup: the sample was irradiated for 5 minutes under 254 nm UV light with UVC irradiance of 3.4 mW/cm ² hitting the sample, after which the afterglow measurement was started immediately with a Hagner Evacuation Route Photometer ERP-105 coupled to a Hagner SD 27 detector. The signal coming from the instrument was converted to volts with a Fluke multimeter. FlukeView Forms PC application reads the value of the multimeter every second, and the value with a certain multiplication factor (depending on the sensitivity setting on the ERP-

105) is used to calculate the actual luminance in mcd/m . Results

Figures 1 to 3 illustrate the decrease of normal afterglow in heat-treated material compared to non-treated material. In these Figures, x-axis stands for “time” in seconds, whereas y- axis stands for “luminance” in mcd/m . The heat-treated materials (for one hour in each Figure) are shown with the curves on the left, while the non-treated material is shown with the right-most curve in each Figure. The material tested was MT13 in Figure 1, MT24 in

Figure 2 and MT43 in Figure 3. The luminance fading time to the 0.3 mcd/m level of MT13 heat treated at 500 °C was 6 minutes vs. 28 minutes for the non-heat treated material. These values were 4 minutes vs. 14 minutes for MT24 and 1 minute 50 seconds vs. 5 minutes 40 seconds for MT43 (each heat treated at 500 °C). From Figures 1 to 3 it can be seen that heat-treatment considerably decreases the afterglow. The Figures also illustrate the effect of the temperature. For the material MT13 (Figure 1), the optimal temperature was found to be 600 °C, the other treatment temperatures being then in the following order: 500 °C, 400 °C, 300 °C, 700 °C and 200 °C, while for this material the temperature of 850 °C for one hour was too much (the curve is practically non-existent, as the material deteriorated during the treatment). For the material MT24 (Figure 2), the order from shortest time to longest time was: 850 °C, 600 °C, 500 °C, 400 °C, 200 °C, 800 °C, 300 °C and non-treated. For the material MT43 (Figure 3), the order was: 850 °C (again slightly too high), 600 °C, 500 °C, 700 °C, 400 °C, 300 °C, 200 °C and non-treated.

Figure 4 illustrates the effect of time of heat treatment on the normal afterglow, the normal afterglow being measured as for Figures 1-3. The materials tested were MT24 at 500 °C for 1 or 2 hours, and MT43 at 500 °C for 1 or 2 hours. The empty symbols in the graph show the results for treatment for 1 hour and the full symbols the results after treatment for 2 hours. The effect of increasing the time thus had an effect on the afterglow, the longer treatment decreased the afterglow more, while the difference between the two materials were not exactly identical.

Figures 5 and 6 illustrate the increase of intensity of optically stimulated luminescence in heat-treated material. The tested materials were MT80 (400 °C, 500 °C and non-treated) in Figure 5 and MT 82 (400 °C, 500 °C, 600 °C and non-treated) in Figure 6. The Figures show the OSL intensity on the y-axis (logarithmic scale) and time (in seconds) on the x- axis. In Figure 5, the curves for 400 °C and 500 °C practically overlap, while the curve for the non-treated material is clearly lower, i.e. the intensity of the OSL is significantly lower. In Figure 6, the uppermost curve is for 600 °C, while the curves for 400 °C and 500 °C are again rather closely overlapping. The curve for the non-treated material is the lowermost.

Figure 7 illustrates the effect of heat treatment and electron bombardment on the intensity of optically stimulated luminescence according to an embodiment. The sample was MT82, heat-treated and then electron bombarded as explained above. Figure 7 shows the results stacked, for better visual assessment. The scale on y-axis in Figure 7 is thus not representative, only the differences in the different lines. The upper line shows the result for the heat-treated but not electron bombarded sample MT82a, while the lower line is for the sample treated at 600 °C, followed by electron bombardment for 20 minutes (sample MT82b). As can be seen, the increase in OSL intensity is clearly higher for the sample MT82b.

Figures 8 and 9 illustrate the effect of an UV radiation on CR image. The material used in Figure 8 was MT55 (Example 3a) and in Figure 9, the material was MT57 (Example 3a). In both Figures the left-most picture is the plate prior to UV treatment. The lower half of both plates was treated with one UV treatment (302 nm/20 min/4.25 mW/cm ² ), whereas the upper half was left untreated. After the UV treatment, X-rays (80 kV, 25 mA) were used to produce the image. The different pictures show the image of the plate after different amounts of X-ray exposures. In both Figures, the second plate was exposed to X- rays ten times (total dose 101 mGy), the third plate 8 times (total dose 80 mGy), the fourth plate 5 times (total dose 50 mGy) and the fifth plate 1 time (total dose 10 mGy), when reading from left to right.

Thus, it can be seen from Figures 8 and 9 that there is a much higher contrast, i.e. the signal is more intense, of the CR image in the region (lower half) which was subjected to UV treatment. The Figures also show that the UV treatment gives a readable CR image also at lower X-ray doses, which is not the case with a corresponding material without the UV treatment.

Figures 10 to 12 illustrate ultraviolet enhancement of polymer emission, i.e. without any material according to formula (I), obtained according to Example 3c. The tape-cast polymer as explained above was used in Figures 10 and 11, while the polyester projector transparency was used in Figure 12. In each experiment, unexposed and UV-treated tape- cast polymers were compared. All the Figures represent intensity (a.u., on the y-axis) as a function of wavelength (nm, on the x-axis). The measurements were an average of 10 measurements, with 1 second integration time.

From Figure 10, it can be seen that the UV-treated polymer, which is the upper curve between wavelengths of about 450-485 nm, thus has a more intense blue emission. Figure 11 , in turn, shows the excitation spectra for blue emission for unexposed (marked with squares) and UV-treated polymer (marked with spheres), wherein it can be seen that the UV-treated polymer has a broader excitation band, which is thought to be the reason for brighter blue emission.

Finally, Figure 12 shows emission spectra of unexposed and UV-treated polyester transparency. From the Figure it can be seen that two different emission bands of this polymer (420 nm and 480 nm) are both enhanced by UV treatment.