Preparation And Luminescent Properties Of Rare Earth Doped SrMoO₄ Phosphors For Leds

The white light emitting diodes （LEDs） have received increasing interests in recent years for its energy-saving and environment-friendly features on the new-type lighting sources. The phosphor-conversion white LED becomes the main method on commercial production. Thus, it is urgency to search novel red or white phosphors which can be excited effectively by blue light or near-ultraviolet （UV） light and show high color rendering index. The main purpose of this work is to obtained red, green or white phosphors for the near-ultraviolet based white LEDs. SrMoO₄:Eu³⁺,SrMoO₄:Tb³⁺ and SrMoO₄:Eu³⁺,Tb³⁺ are prepared and their crystal structure, luminescent properties and energy transfer have been studied. The main contents and results are listed below.1. The SrMoO₄:Eu³⁺ red phosphors have been prepared by co-precipitation method. The XRD patterns showed that the SrMoO₄:Eu³⁺ was a pure phase with a tetragonal structure. The strong transition （613nm） was observed, originating from the 5D0â†'7F2 transition of Eu³⁺ ions. The excitation spectrum of the SrMoO₄:Eu³⁺ red phosphors consisted of a broad band peak and a series of sharp peaks, and since the strong peaks were located at 280nm （the broad band center）, 395nm and 465nm, respectively, thus the phosphor can be excited effectively by the UV LED and Blue LED. The energy transfer was observed from the host to the Eu³⁺ ions. The Eu³⁺ ions concentration has a great influence on the crystal parameters, the crystal symmetries and the luminescent properties. The influence of different concentrations doped Eu³⁺ions on the luminescent intensity of SrMoO₄:Eu³⁺ was studied and the optimal doping concentration was 15%.2. The SrMoO₄:Tb³⁺ green phosphors have been prepared by co-precipitation method. The XRD patterns showed that the SrMoO₄:Tb³⁺ was a pure phase with a tetragonal structure. The emission spectrum excited by 379nm showed a strong emission peak at 543nm, originating from the ⁵D₄â†'7F5 transition of Tb³⁺ ions. While monitoring 543nm emission from Tb³⁺, the energy transfer was observed from the host to the Tb³⁺ ions. The phosphor can be excited effectively by the UV LED and Blue LED. The doped Tb³⁺ ions concentration and sintering temperature have a great influence on the crystal orientation, crystal parameters and the luminescent properties. The effect of different concentrations doped Tb³⁺ions on the emission intensity of ⁵D₄ and ⁵D₃ transition was studied,and the energy transfer between Tb³⁺ions. The optimal doping concentration for the luminescence of Tb³⁺ was 10%.3. A series sample of SrMoO₄:xEu³⁺,5%Tb³⁺ phosphors were prepared by the chemical co-precipitation method. The white light emission of SrMoO₄:Eu³⁺,Tb³⁺ under 379 nm excitation is observed. The emission spectrum showed two bands, which were attributed to Tb³⁺ and Eu³⁺ respectively, and the energy transfer between Eu³⁺ and Tb³⁺ was observed. The light color can be tunable by varying the rare earth ions concentrations. The excitation wavelengths affect the intensity of red, green and blue lights, and sintering temperature have a great influence on the crystal parameters and the luminescent properties. Thus,the SrMoO₄:Eu³⁺,Tb³⁺ phosphors could emit white light by changing the doping concentration of Eu³⁺ and Tb³⁺, excitation wavelengths and sintering temperatures.