luminescent crystal
2.ZnS、CdS are both the direct bandgap semiconductor compound. In ZnS, the Zn is replaced by Cd~2+,It arouses the descend of the bottom of the conduction bandand. So it makes the forbidden bandwidth of the luminescent crystal change, the energy level of luminescence center changes immediately, therefore the luminescence spectrum is changed continuously.
4.Because Eu2+ is surrounded by host ions, mixed states of 4f5d will be split by the crystal field and the luminescent wavelength will be changed.
5.CaSO4:RE(La,Y)them-selves could not emit fluorescent light,the addition of Y3+ and La3+ ions had no effect on crystal lattice of matrix,but could enhance the luminescent intensity of CaSO4; Eu2+.
6.hi this paper, the Y_2O_2S:R~(3+),Mg~(2+),Ti~(4+)(R~(3+)=Eu~(3+),Sm~(3+),Tb~(3+)) phosphors were synthesized first by co-precipitation method. Its x-ray diffraction patterns, the structure of crystal lattice and the luminescent properties were studied.

