Synthesis And Properties Of Titenate Phosphors For White LEDs

In the 21st century, white light emitting diode (WLED) is a remarkable lighting source because it possesses such excellent performance as high luminescence efficiency, long life time, low power consumption, and environment friendly, and so on. Therefore, it is promising for the market applications. The main approach to obtain WLED is phosphor-converted. But the efficiency of the commercial Y2O2S:Eu3+ red phosphor is about 8 times less than that of the green and blue phosphors. In addition, sulfide-based phosphors are chemically unstable in atmosphere and not environmentally friendly, which are bottlenecks to limit the development and application of the WLED.In this paper, micro-tube red phosphors CaTiO3:Eu3+, which could be excited by NUV light, were prepared via solvothermal method. The phosphors were characterized by X-ray diffraciton (XRD), scanning electron microscope (SEM), fluorescence spectrophotometer(PL) and solid quantum efficiency (SQE). XRD spectra revealed a well-defined crystalline structure without impurity phases for doped samples. The SEM revealed the regular shape and good distribution of the phosphors synthesized by the mixture of ethanolamine and ethanediamine. The morphology could be modulated by the temperature and solvent. The CaTiO3:Eu3+ phosphors showed emission peaks from 575 to 720 nm and the maximum emission wavelength was at 617.6 nm under the near-ultraviolet excitation (400nm). The internal quantum efficiency of CaTiO3:Eu3+ synthesized by solvothermal method was measured as 58.34%, much higher than the solid solid-state method and much close to the Y2O2S:Eu3+. These properties make the CaTiO3:Eu3+ phosphor a promising red phosphor which can substitute for Y2O2S:Eu3+ phosphor to be used for commercial WLEDs. The concentration quenching and different solvents of the samples were discussed as well. The optimal concentration and the temperature were 3 mol% of Eu3+ for these phosphors, and the possible reason was discussed as well. Micro-tube CaTiO3:Eu3+ is a promising red phosphor under near ultraviolet excitation for various applications. In order to seek more excellent red phosphors, the La2Ti2O7:Eu3+phosphors were synthesized by solid state reaction method. XRD spectra showed a well-defined crystalline structure without impurity phases for doped samples. The crystalline La2Ti207:Eu3+ phosphors showed emission peaks from 575 to 720 nm and the maximum emission wavelength was at 612 nm. Because this phosphor was efficiently excited by 465 nm, it can well match the blue LED Chips. The WLED fabricated by coating a mixture of Y3Al5012:Ce3+ and La2Ti207:Eu3+ onto blue InGaN chip showed higher color rendering index than the Y3Al5O12:Ce3+- WLED and its good thermal stability can meet the demand of high-power LEDs. The emission intensity increased steadily with the increasing of the calcination temperature till 1500℃. The optimized Eu doping concentration was found to be 30 mol% for the emission intensity reached the top. The phosphor obtained by our experiments could find extensive applications in high-power commercial Y3Al5O12:Ce3+- WLEDs.To improve the luminescence properties of the phosphors, La2Ti2O7 was chosen as a lattice, Sm3+/Y3+ had been co-doped with Eu3+. In the experiments, the Eu3+ (5%) doped phosphor had been chosen as a frame of reference. Compared with the La2Ti207:Eu3+, the La2Ti207:Eu3+, Sm3+ showed stronger red emission and broader excitation band. The La2Ti207:Eu3+, Y3+ also showed stronger red emission. The concentration quenching of the samples was discussed and the energy transfer was discussed as well.