Luminesence Properties Of （NaNbO₃）_1-X（NaLaTi₂O₆）_X/2:Pr³⁺ Phosphors

Phosphors are very important in white light Light-emitting diodes. Traditional phosphors usually based on the silicate, phosphate and sulfates. Recently, rare-earth doped niobates and titanates have drawn much attention, such as CaNb2O6:Pr3+, :xEu3+. In the niobate and titanate phosphors, large splitting of 5d energy levels, which make the decrease of 5d-4f energy level difference, which make them as a potential monochromatic light.The structures and luminescence properties of (NaNbO3)1-x(NaLaTi2O6)x/2 were investigated in this thesis. That the diffraction peaks of the (NaNbO3)1-x(NaLaTi2O6)x/2:Pr3+ shifted to the larger-angle with the increase of x. It is confirmed that a new type of solid state solution was synthesized. The excitation spectra exhibit one dominated band at 278 nm and two shoulder bands in ultraviolet region, which are located at about 334 and 361 nm, respectively. The main absorption band at 278 nm can be regarded as the charge transfer transition NbO43- and TiO68-. The band at 334 nm can be assigned to the charge transfer state:Ti4+_O2_to Ti3+_O-. The band at 361 nm is resulted from a charge transfer state:Pr3+-O-Ti4+ to Pr4+-O-Ti3+. The photoluminescence spectra showed the red emission peaks at 612 nm which are originated from the transitions of1D2 â†' 3H4 of Pr3+ ions. The green emission peak at 498 nm is also observed which are originated from the transitions of 3Po â†' 3H4 of Pr3+ ions. With the increase of value x in (NaNbO3)1-x(NaLaTi2O6)x/2: Pr3+, the intensity ratio between red and green emission (IR/IG) increases until x= 0.5, decreases after that. The Commission International de l’Echairage (CIE) moves from (0.52,0.37) to (0.65,0.34). The fluorescence lifetime time of (NaNbO3)1-x(NaLaTi2O6)x/2:Pr3+ were also measured. Their fluorescence lifetime is about 5 Ms. With the La3+ ion was replaced by Ca2+ ion gradually, the luminous intensity of Na0.75La0.25-xCaxNb0.5Ti0.5O3:Pr3+ were enhanced. The emission peak intensity of Na0.75La0.25Nb0.5Ti0.5O3:Pr3+ is enhanced about 1.78 times.