Preparation And Luminesence Properties Of Rare-Earth Doped NaCaTiMO₆（M = Ta, Nb） Phosphors

In this thesis, the phosphors NaCaTiMO6:Pr3+(M=Ta, Nb), NaCaTiNbO6: Pr3+,Bi3+ and NaCaTiNbO6:Pr3+,Bi3+,In3+ had been prepared by solid-state reaction, their crystal structure, decay time of the rare earth ions, afterglow time and photoluminescence properties were investigated.The XRD patterns for these NaCaTiMO6:Pr3+(M=Ta, Nb) phosphors were measured. It can be indexed on the basis of orthorhombic perovskite structure of space group pnma. With increasing x, the diffraction peaks of the NaCaTiMO6:Pr3+(M=Ta, Nb) slightly shift to the left, but there is no impurities appear, so we synthesized the sample that we needed. The excitation spectra mainly consists of one dominated band at 360 nm and two shoulder bands in ultraviolet region, which are located at about 274 and 346 nm, respectively. The main absorption band at 360 nm which re’sulted from a charge transfer state (CTS):Pr3+-O-Ti4+ to Pr4+-O-Ti3+; the band at 274 nm can be either the overlap of a charge transfer transition Pr4+-O2- to Pr3+-O- and the band at 346 nm is assigned the valence-to-conduction band transition (Ti4+-O2- to Ti3+-O-). And some weak excitation peaks within the scope of 450-500 nm may ascribed to the f-f transitions of Pr3+ from 3H4 to 3P2,3P1,1I6 and 3Po, relatively. After Ta5+ ions completely replaced by Nb5+ ions, the emission intensity of phosphors reached its maximum value.In order to increase the luminous intensity of NaCaTiNbO6:Pr3+, the Bi3+ ions was added to it. The XRD patterns of NaCaTiNbO6:Pr3+,Bi3+ were similar to the standard card (JCPDS#22-0153). The NaCaTiNbO6:Pr3+,Bi3+phosphor shows a wider absorption in the region which ranging from 250 to 375 nm. The enhancement of UV excitation intensity originates from the strong absorption transition of 1S0 to 3P1 state of Bi3+ and Bi3+ ions play a role as sensitizers; the PL intensity of NaCaTiNbO6:0.5%Pr3+ is enhanced 2.1 times by the introduction of Bi3+ ions, which is attributed to the energy transfers from Bi3+ to Pr3+. By measuring the decay time of Pr3+ of NaCa0.995-xTiNb06:0.5.%Pr3+,yBi3+(y=0、0.3%、 1%) phosphor, we find that with Bi3+ ions added, the decay time of Pr3+ ions also increases, further proved that the energy transfers from Bi3+ to Pr3+. The afterglow time of NaCa0.995-yTiNbO6:0.5% Pr3+,yBi3+(y=0、0.3%) also were measured, their afterglow times are about 300s.At last, we added charge compensation In3+ to NaCaTiNbO6:Pr3+,Bi3+ to improve the luminous intensity of it. The XRD patterns of NaCaTiNbO6:Pr3+,Bi3+,In3+ were also similar to the standard card (JCPDS#22-0153). The PL intensity of NaCaTiNbO6:Pr3+,Bi3+ is enhanced 1.31 times by the introduction of In3+ ions, which is attributed to the charges reached the equilibrium state and formed relatively stable luminescent center in crystal.