Research On Luminescent Properties Of Tungstate Phosphors Under UV/NUV Excitation

White light emitting diodes（LEDs） have been widely applied in large outdoor architectural lighting, traffic lights and phone screen display and so on. Simultaneously, they are regarded as the next generation solid state light source for their many excellent properties such as fast response, long lifetime, high efficiency, saving energy, high stability and environmental friendliness, etc. The synthesis methods of white LED including the following three types: the first is to use red, green, blue three kinds of the LED chips to produce white light. It is necessary to produce the corresponding three circuits, this will increase the cost of production to some extent. So this type is not conducive to the popularity of LED in the market; The second is to use blue chip excite the yellow phosphor to produce white light; However, the color rendering index（CRI） and the correlated color temperature（CCT） is not ideal of the white LED due to the scarcity of green and red component in the emission spectra. The third is by using ultraviolet or near ultraviolet chip and the combination of red, green, and blue phosphor to produce white light. It also exists the problem of color reabsorpion and the disproportion of different phosphors in this kind of production. In order to overcome these problems, we focus on the research direction of this paper as follows:（1） investing stable green and red phosphors to combine with the UV/NUV chips;（2） developing the single phase white phosphors that can be efficiently excited by UV/NUV light.The high temperature solid state reaction method has always been the widely used way for its simple process and good crystallinity of samples. In this paper, we have successfully synthesized the red and the single phase white phosphors for white LEDs on tungstate substrate due to its stable properties and lower synthesis temperature, by using high temperature solid state reaction method. We also researched the relationship between luminescent properties of the doped rare earth with the lattice surrounding environment. The specific contents of research are shown as follows:（1） Tb³⁺ doped Li₃Ba₂Y₃（WO₄）₈ phosphors were successfully synthesized by using a high temperature solid state reaction method. In Tb³⁺ singly doped phosphors, the substrate itself has a certain intensity of blue light emission when doping concentration is x=0.1 or lower; Later, with the increase of concentration of Tb³⁺, the blue emission from substrate itself will become reduce. Emission spectrum of phosphor reached the peak at the green area（550 nm）. In addition, the variable temperature spectra and activation energy of the analysis showed that this fluorescent powder possess good thermal stability.（2） A series of Eu³⁺ doped Li₃Ba₂Y₃（WO₄）₈ phosphors are prepared by high temperature solid state method. It was found that the phosphors also have a high intensity of red light emission and high color purity under the NUV 394 nm excitation. Through the calculation of J-O theory, it can be deduced that the Eu³⁺ transition rate in this powder is higher, so Li₃Ba₂Y₃（WO₄）₈ phosphors possess the high quantum efficiency. We also concluded that the substrate refractive index was 2.21 and thermal stability studies show that the phosphor has excellent thermal stability.（3） In the present work, Tb³⁺/Eu³⁺ co-doped Li₃Ba₂Y₃（WO₄）₈ phosphors were synthesized via a high temperature solid state reaction method. It was found that by using the blue light emission of substrate itself, by adjusting the proportion of Tb³⁺ and Eu³⁺, phosphor luminescence would come from green to white light area. At the same time, the fluorescent powder also possesses good thermal stability.