Synthesis And Luminescence Properties Of Praseodymium-doped Calcium Titanates Persistent Phosphors

Rare earth praseodymium doped calcium titanate persistent phosphor is chemically and thermally stable complex oxide, which is known for several years as a red emitting phosphor characterized by a single emission peak with chromaticity coordinates, very close to the coordinates of the"ideal red". In this paper, the preparation methods, luminescence mechanism and influence factors of praseodymium doped calcium titanates were introduced. The various synthesis methods (including sol-gel, modified solid-state, combustion and coprecipitation methods) were employed to prepare the persistent phosphors.Red CaTiO₃: Pr³⁺, Al³⁺ persistent phosphors have been synthesized by sol-gel method using ethanol as solvent and citric acid as a chelating agent. TG-DTG curves and X-ray diffraction analysis indicate that crystalline calcium titanate has been synthesized at calcining temperature of 700℃for 5 hours. Photoluminescence and decay curves indicate that the luminescence properties of phosphors synthesized by sol-gel method are better than that prepared by solid-state reaction and the sample heated at 900℃exhibits the optimal luminous property. Using ultrasonic dispersing technique improved the luminescence properties of phosphors.Using tetra-n-butyl titanate and calcium nitrate as raw materials, the praseodymium-doped calcium titanates have been synthesized via a modified solid-state reaction. The decomposition process of the precursor, crystallization, and particle sizes of CaTiO₃: Pr³⁺ have been investigated by using thermal analysis, powder X-ray diffraction and transmission electron microscopy. TG-DTG curves and X-ray diffraction analysis indicate that crystalline calcium titanate has been synthesized at calcining temperature of 600℃for 2 hours. Photoluminescence and decay curves show that the sample obtained at the sintering temperature of 900℃exhibited the optimal luminous property.Using urea as fuel and boric acid as flux material, red persistent phosphors CaTiO₃: Pr³⁺,Al³⁺ have been successfully synthesized by combustion method. The process lasted for less than 5 min and led to the formation of voluminous white powder. The photoluminescence, crystallinity and particle morphology of persistent phosphors were investigated by using luminescence spectrometer, X-ray diffractometer (XRD) and transmission electron microscopy (TEM), respectively. The results showed that the boric acid was effective in improving the photoluminescence intensity of CaTiO₃: Pr³⁺, Al³⁺ phosphor particles and the optimum molar ratio of boric acid to calcium nitrate was about 0.4. The luminescent properties and crystallinity of phosphors increased with increasing initiating temperature.Using tetra-n-butyl titanate, calcium nitrate and oxalic acid as raw materials, the praseodymium-doped calcium titanates have been synthesized via calcinations of oxalate coprecipitated precursors. The decomposition process of the precursor, crystallization, and particle sizes of praseodymium-doped calcium titianates have been investigated by using thermal analysis, powder X-ray diffraction and transmission electron microscopy, respectively. Photoluminescence of the sample obtained at 900℃was examined by luminescence spectrometer, and the brightness of persistent phosphors indicate that the luminous property of the samples was enhanced with increasing sintering temperature.