EXCITABILITY FOR LIGHTING AND OPTICAL APPLICATIONS Technical Field

[0001] The present invention relates to so-called red emitting ceramic phosphor materials which can be phosphor particles, two dimensional ceramic sheets and pellets as well as crystalline and polycrystalline depending on the prepare methods. Such luminescent particles have been shown to exhibit important properties that may be exploited in various optical applications. In particular, the present invention relates red emitting phosphor with controllable excitability that is particularly produced by a sol-gel method as well as high-temperature solid-state reaction, which is compatible for mass production.

[0002] Eu has been used widely as red emitting powder, but its excitability is limited to UV and near-UV region. In this invention, the involved luminescent material is a red emitting, which is typically based on Eu ³⁺ based phosphor with selective excitability in blue and green region.

Background Art

[0003] Photo-luminescent materials are often referred to as phosphors, which are typically characterized by excitation and emission spectra, which is based on the excitation in certain absorption range and recording the emission accordingly. [0004] The photo-luminescent particles, which could be used in lighting (LED/ Laser diode phosphors), display technologies, catalysts (with indicator), humidity sensors, batteries, biosensors, biomarkers, and security inks. Eu ³⁺ based red line emitting phosphors lack of efficient excitation in the blue region. These objects mentioned above are obtained as specified in the accompanying claims.

[0005] The red emitting ZnMo0 ₄ : Eu ³⁺ as a luminescent material already exists but increased selectivity of excitation at 465 and 536 nm is not present. However, in our invention Manganese (Mn) incorporation provides enhanced and selective increase at 465nm and 536 nm respectively. Additionally, we can produce, bottom-up, polycrystalline polydisperse particles and nano thick macro sheets of ceramics particularly through sol-gel method [1] If we look at the previous similar inventions [2, 3], none of them has the same intense selective increase at 465 and 536 nm in excitation spectra. In our finding, Manganese (Mn) incorporation to known ZnMo0 ₄ : EU ³⁺ ceramic composition, provides superior and selective electronic transition instead of other rare earths (like Tb ³⁺ , etc.) or Bismuth, Na, K, Li charge compensators for

EU ³⁺ .

[1] Lakhlifi et ah, Synthesis and physicochemical characterization of pigments based on Molybdenum « ZnO-MoCh: Co ²⁺ », J. Mater. Environ. Sci. 6 (12) (2015)

3465-3469.

[2] Li-Ya Zhou et al“A potential red phosphor ZnMo0 ₄ : Eu ³⁺ for light-emitting diode application”; Journal of Solid State Chemistry, Vilume 181, Issue 6, June 2008, Pages

1337-1341, [3] Neha Jain et al.,“Enhanced photoluminescence behaviour of Eu ³⁺ activated ZnMo0 ₄ nanophosphors via Tb ³⁺ co-doping for light emitting diode”, Journal of Luminescence, Volume 188, August 2017, Pages 504-513, Summary of the invention

[0006] The present invention is based Eu doped and Mn co-doped ZnMo0 ₄ , Eu _x , Mn _y : Zni- _x-y Mo0 ₄ . As Eu and Mn molar percentage is adjusted according to the invention, the luminescent intensity and surface structure of the powder changes.

[0007] According to the invention, as an example the Euo.2, Mno.i : Zno. ₇ Mo0 ₄ has elongated/one-dimensional nano thick macro sheet structure (flakes) consisting of polycrystalline polydisperse particles.

[0008] In many synthesis routes, solid state reaction method has been used requiring high temperatures. Co -precipitation method has been also provided. Here we provide particularly sol-gel route to Eu _x Mn _y Zni- _x-y Mo0 ₄ .

[0009] According to a first aspect of the present invention there is provided a ceramic pellet can be used as product for high power lighting and display systems. The excitation below 550 nm, particularly at 465nm and 536 nm provides the maximum efficiency.

[0010] In molar Eu percentages 5-25 % and Mn molar percentages of 5-20 %, the formed luminescent particles are poly crystalline polydisperse particles (2-12 pm) to wherein the size of said flakes are in the range of 5- 1 OOpm consisting of 0.1-10 microns polydisperse, polycrystalline particles. [0011] According to a second aspect of the present invention there is provided a method of producing polycrystalline polydisperse mesoporous luminescent particles. The method comprises the following steps:

[0012] a) Mixing the stoichiometric amount of nitrates in citric acid

[0013] b) Drying to gel.

[0014] c) Precalcination of the formed gel;

[0015] d) Calcination of the precalcinated powder.

[0016] Step d) includes the following steps:

[0017] i) In a muffle furnace, heating the precalcined gel at 500-600 °C for 1-3 hours and calcination at 650 - 850 °C for 4 - 6 hours. .

[0018] ii) The following phosphor ceramics are pressed under 2-3 MPa in 1 or 2 cm diameters and sintered at 600-800 °C for 2-4 hours, producing densed ceramic pellets..

Detailed description of the invention

[0019] The invention will be described more in detail below with reference to the drawings, illustrating the invention by way of examples:

Fig. 1 illustrates scheme of sol-gel synthesis route for E¾M Zh _ΐ-c-g Mo0 ₄ . The ceramic particles can typically be produced with sol-gel synthesis. Average size changes with different Eu and Mn molar percentages and diameters of the phosphor ceramics can be between 0,1 to 12 pm.

Fig. 2 depicts the excitation spectrum of (Eu _x Mn _y )Zri _(i-x-y) Mo0 ₄ .

Fig. 3 illustrates as an example the excitation and emission spectra of EUO.2, Mno.i: Zno. ₇ Mo0 ₄ .

Fig. 4 as an example shows the SEM images of Euo.2, Mno.i: Zno. ₇ Mo0 ₄ consisting of polycrystalline, polydisperse, mesaporous network with nano-thick macro sheets and flakes.

Fig. 5 indicates the color coordinates of the luminescence of powders Eu _x , Mn _y :

Zni- _x-y Mo0 ₄ powders wherein molar Eu percentages ranges 5-25 % and molar Mn percentages 5-20 %.

Sol-gel synthesis of Eu _x . Mn _y : Zni_ _x-y Mo0 ₄

[0020] Modified sol-gel synthesis route can be used for the production of Eu ³⁺ - Mn doped ZnMo04 material constituting red emitting Eu _x , Mn _y : Zni_ _x-y Mo0 ₄ ceramic powders. Increasing molar x values from 5% to 25% provides the maximum emission control together with optimized y % content for Mn co-dopant which is 5 to 20 %. Such a process is known to the person skilled in the art, and will not be discussed in detail herein. In The figure 1 an example of such a process is illustrated where the raw materials, aqueous Mh(N0f·4H ₂ q, (NH ₄ ) ₆ Mo ₇ q ₂₄ ·4H ₂ q, EiANOfAIfO, and citric acid with solid (O,FOt^ZhFIfO may be used to produce a stochiometric solution. As the first step, the calibration may be done for determining accuracy water content due to water absorption in storage. As the second step, the four raw materials will be weighted with stoichiometric forming (Eu _x Mn _y )Zn(i- _x-y )Mo0 ₄ compound. As the third step, the Gel will be prepared by evaporating the water in the mixed stoichiometric solution of the four raw materials. The solid-state reaction, e.g., calcination in air or demand atmosphere will be performed to make phosphor material

(Eu _x Mn _y )Zri _(i-x-y) Mo0 ₄ . Figure 1 also disclose the use of Cu or Mg instead of Mn, which is a possibility that could provide emissions at other wavelengtrhs but are not a part of the present invention.

[0021] After producing the gel, gel is pre-calcined at 275 - 325 °C and following calcination process at 500-600 °C for one to three hours and at 650-850 °C for four to six hours. Fig. 4 shows examples of Scanning Electromagnetic Microscope (SEM) images of the resulting Eu0.2, MnO.l: Zn0.7MoO4 consisting of poly crystalline, polydisperse, mesoporous network with nano-thick macro sheets and flakes (4).

[0022] Specifically, ceramic pellet may be produced from this with a base pressure of

2-3 MPa in 1 or 2 cm diameters and sintered at 600-800 °C for 2-4 hours, giving dense luminescent ceramics.

Luminescence performance

[0023] Fig. 2 illustrates the excitation spectrum of Euo.2, Mno.i:Zno. ₇ Mo0 ₄ and as indicates the main excitation wavelength is moved (2) from the ultraviolet (LTV) range at approximately 300nm to 465nm. Fig. 3 depicts the measured emission and excitation spectrum of the same material or radiation source according to the invention. As mentioned above excitability at 465nm more favorable than UV and near UV excitation and the material exhibite red luminescence at approximately 615 nm (3), thus proving an advantage over the known art.

[0024] Fig. 5 depicts the calculated CIE 1931 coordinates according to the invention; the color coordinates (0.67, 0.32) (5), with the quantum yield of 90 %. [0025] Red luminescence is stable up to 200 °C.

[0026] To summarize the present invention relates to an excitable radiation emitter material, more specifically the material being a red emitting ceramic phosphor particles being excited within a certain range of wavelengths and emitting light in the red part of the visible spectrum. The invention also related to a light source incorporating the emitter material and methods for production of the material. The material comprising a ZnMo0 ₄ host material being doped with Eu ³⁺ and co-doped with Manganese (Mn). The material preferably being constituted by a poly crystalline poly disperse, mesoporous, nano thick, macro ceramic flake with a molar percentages in the range of 5-25 % Eu and 5-20 % Mn, as an example Euo.2, Mno.i :Zno. ₇ Mo0 ₄ is given. The size of the flakes are preferably within the range of 5- 1 OOmhi consisting of 0.1-10 microns polydisperse, polycrystalline particles.

[0027] The invention also relates to an emission source emitting red light including a light source emitting light in the range less than 550nm and especially in the excitation wavelength of the emitter material at 465nm as well as possibly 535nm. The exited emitter material will then emit radiation in the range above 550nm, and especially at or close to 6l6nm.

[0028] The emitter material is applied directly onto the light source, e.g. as a paint on the light source surface, or close to the light source being illuminated thereby from a chosen distance, and depending on the use filters may be used to remove the excitation wavelengths from the signals emitted from the light source. If the light source and the emitter material is positioned in different location it is also possible to remove the excitation wavelengths by shielding the light source..

[0029] As stated above the method for providing the luminescent ceramic particles has been sensitized through sol-gel as well as high-temperature solid-state reaction, for example utilizing a sol-gel process comprising the following steps:

a) Mixing standardized nitrate solutions of Mn, Eu, Mo and Zn in citric acid (2:1 ratio according to cation concentration) (1) in deionized water at 100 - 130 °C for 8 - 10 hours.

b) Evaporation of solvent and gel formation

c) Pre-calcination of the gel at 275 - 325 °C

[0030] Preferably the step c) is followed by a step d) comprising a calcination process, where the calcination process includes the calcination steps of:

i) In a controllable furnace heated to 500-600 °C, exposing the sample (1) in air for 1-3 hours. Then calcined at 650-850 °C for 4-6 hours leading to the formation of luminescent ceramic.

ii) The produced phosphor ceramics are then pressed under 2-3 MPa in 1 or 2 cm diameters and sintered at 600-800 °C for 2-4 hours, producing densed ceramic pellets.