Effect Of Ca Deviations On The Photoluminescence Of CaTiO₃:Pr³⁺

Recently,rare-earth-doped oxide phosphors have attracted considerable attention because of their application to flat panel displays(FPDs),including field-emission displays (FEDs).In order to enhance the luminous properties,many researchers have studied these phosphors varying the concentration of activator ions,different charge compensators, surface morphology of the films,grain size of the powders and different synthesis methods. Among a lot of rare-earth-doped oxide phosphors,we focused on Pr³⁺doped CaTiO₃ phosphor as our target.Firstly,different Ca deficiencies on photoluminescence of CaTiO₃:Pr³⁺powders were investigated.Secondly,we prepared citric acid added CaTiO₃:Pr³⁺films on Si substrate by sol-gel method.Firstly,Ca_1-x-yPr_xTiO₃ powders were fabricated by a Sol-Gel method,and their microstructure,photoluminescence and afterglow properties were explored.Specially, different y values were adopted to investigate the effect of Ca deficiency on the luminescent properties of the powders.An increase in the fluorescence intensity at 613 nm was observed when x=0.25 mol%and y increases from 0 to 1.5x.Similar result was found for x=0.15 and 0.35 mol%.Increased afterglow was observed for samples having low y values after irradiated by 375 nm light.Such effect was ascribed to the formation of trapping centers related to[Pr_Ca]°defects when they are not compensated by[V_Ca]".These results indicated that the traditional adopted formula Ca_1-3x/2Pr_xTiO₃ which is charge compensated as a whole sample may not be the best one for its efficient red photoluminescence.Secondly,we prepared Ca_1-x-yPrTiO₃ powders by Sol-Oel method.Microstructure photoluminescence and afterglow properties are all similar to Ca_1-x-yPrTiO₃ powders. Highest fluorescence intensity at 613 nm was observed when x=0.25 mol%and y=1.5x, which is 1.5 times of y=0.The reason is up to more experiments. Finaly,Red-emitting CaTiO₃:Pr³⁺phosphor thin films were deposited on Si substrates by Sol-gel process and annealed in air at temperatures ranging from 500 to 1000℃.In this work,citric acid was added into solution of CaTiO₃:Pr³⁺as a surface modifier to investigate its effect on photoluminescence properity.The crystalline structure and microstructure of these films have been characterized by X-ray diffraction and atomic force microscope and their luminescent properties have been evaluated at room temperature using a luminescence spectrometer.The crystalline phase and surface morphology of the films were strongly dependent on the annealing temperature and they affected the luminescent brightness of the films.In particular,the addition of citric acid into CaTiO₃:Pr³⁺could induce a remarkable increase of photoluminescence.The enhancement of luminescence for citric acid added films may result not only from the improved crystallinity but also from the reduced internal reflections caused by rougher surfaces.