PURPOSE: To improve the brightness, and the contrast by vacuum depositing a simple substance, mixture and compound of chemically stable metal having large ionic radius simultaneosly with cesium iodide thereby forming an impurity layer at the circumference of cecium iodide pillar crystal body.

CONSTITUTION: A fluorescent substrate 5 is arranged in a vacuum chamber 4 of a vacuum evaporator 3. Furthermore a pot 7 containing a fluorescent body 6 such as activated cesium iodide CsI and a pot 9 containing a impurity 8 of simple substance, mixture or compound of mechanically stable metal having high ionic radius such as europium, dysprosium, gadolinium, lanthanum, gold, platinum, terbium, terbium, lutetium are arranged then heated by heaters 10, 11 to vacuum deposit the fluorescent body and the impurity simultaneously. Consequently an impurity layer is formed at the circumference of CsI pillar crystal to limit the light emitted in the crystal within said crystal, resulting in the improvement of luminance and contrast.