The Effects Of Ca Deviation And Zn Doping On The Photoluminescence Of The CaTiO₃: Pr³⁺ Films

Field emission display, FED has been thought to be the next generation of flat panel display technology in industry. It may replace the traditional cathode ray tube and the current liquid crystal display in the future. Phosphor is one of the key technologies for FED. It needs good light-emitting efficiency exicted by the cathode ray and stability. At present, most of reaserch and industry use the small powder mixed with epoxy resins as the coating. However, the luminous films may be more suitable for FED. The advantage of thin films is thermol stability, good uniformity and substrate adhesion. The main disadvantage is the low efficiency of the light emision. CaTiO3: Pr3+ is newly discovered as red fluorescent materials in recent years. It is characterized by structural stability, cheap raw materials, environmental protection, high efficiency light-emitting. A number of studies about its powder have been reported, while the mechanism of the light-emitting is lacking, and the reaserch on the films is just on the beginning. In this study, we prepared the CaTiO3: Pr3+ films on Si substrate by sol-gel method. The effects of Ca deviation and Zn doping on the surface morphology, microstruture, photoluminescence of the CaTiO3: Pr3+ powders and films were investigated.Firstly, we studied the effect of Ca concentration on the photoluminescence of CaTiO3: Pr3+ films. Ca1-x-yPrxTiO3 (x=0.25%, y=-4x, -3x, -2x, -3x, -2x, -3x/2, -x, -x/2, 0, x, 2x, 3x, 4x) films were fabricated on a silicon substrate by a Sol-Gel method, and their microstructure, photoluminescence properties were explored. We found the strongest fluorescence intensity. For Ca deficiency, the strongest intensity of the fluorescence is at y=-x/2, and for Ca excess, the strongest intensity of the fluorescence is at y=3x. The enhancement of luminescence may result from Ca vacancy compensation for Ca deficiency and the substitution of Pr3+ - Ti4+, forming [PrTi], to compensate for the defect of [PrCa]o for Ca excess.The structural and photoluminescent properties of the Pr3+ doped Ca1-xZnxTiO3 (CZT) powders and films were investigated. The Zn concentration affected strongly the red emission of the phosphors. The maximum fluorescence intensity was found to be at x=30%, for both the powders and films. The phosphorescence of the red emission was also enhanced for powders and the largest afterglow happened at x=10%, while the Zn doping had little effect on the afterglow behavior of the films. Charge compensation to the Pr3+ ions using Ca deficiency further increased the fluorescence intensity, but suppressed the red afterglow of the CZT powders. It was demonstrated that the addition of Zn2+ may make the energy transfer more effective from the perovskite host to the Pr3+ ions, leading to the enhancement of both the fluorescence and phosphorescence. However, the phosphorescence was directly related to the amounts of uncompensated Pr3+ ions in the powders.