Preparation And Luminescent Properties Of YAG:Ce³⁺ Phosphors

White LEDs are typically used as illuminators and indicators and used in displays due to low energy consumption, high brightness levels, low operating voltages and longer lifetimes. The white LED is composed of a blue LED chip ((In.Ga)N) and a color conversion layer of YAG:Ce3+ phosphors dispersed in a medium such as epoxy resin. It is based on the principle of integrating two complementary luminescence emissions to generate white light suitable for lighting applications. Part of the blue light from the (In.Ga)N LED is absorbed by the color conversion layer and is converted into yellow light. The combination of blue and yellow gives a bright white light source. Ce3+-doped YAG phosphors have been recognized as the most excellent phosphors satisfactorily applied in vacuum ultraviolet. plasma display panels, solid-stated lasers, and white LED commercial market, because of the high luminescent efficiency and chemical stability. In this article, the development of YAG:Ce3+ photoluminescent materials and photoluminescent mechanism and common preparation methods are introduced. Furthermore, a novel simple method which is called Direct Evaporation Sintering Method (DESM) is proposed for preparing YAG:Ce3+phosphors.In this paper, YAG:CeJ3+ phosphors have prepared by solvothermal method and DESM, respectively. We study the effect of sintering temperature on crystallization properties, surface morphology and luminescent properties of YAG:Ce3+ phosphors. Meanwhile, we pay attention to the behavior of temperature-dependence of luminescence, fluorescence decay lifetimes and quantum efficiency (QE) of prepared YAG:Ce3+ phosphors. which make up the insufficient data of lower temperature luminescent properties of YAG:CeJ-phosphors in the existing literatures. Such as follows:For solvothermal method, the formation temperature of YAG phase is about 900℃, while the pure YAG phase can be obtained at 1000℃. The morphology of the particles can be described as irregular ellipse spherical and the average particle size is about 35 nm. As shown in PL spectra of YAG:Ce3+ phosphors, The excitation spectra are consist of two broad Ce3+ absorption bands peaked at 340 nm and 460 nm. And the emission spectra show a broad emission band with a maximum at 540 nm and located in the range from 500 nm to 700 nm.Compared with the solvothermal method (STM), DESM has some advantages. Firstly, DESM is very simple; reaction product does not need to fast speed centrifugation. water or alcohol washes. So, the problems of products loss and new impurities which are caused by these processes can be avoided. Secondly, the sintering temperature of DESM is lower. According to the XRD results, the pure YAG phase can be generated at 1000℃by STM. and the morphology of the samples is irregularly spherical. While the pure YAG phase can be formed at 850℃by DESM, and the surface morphology of the YAG:Ce3+ phosphors can be described as spherical, and the average particle size is about 30 nm. For the quantum efficiency (QE) of prepared YAG:Ce3+ phosphors, the QE of DESM is 9% higher than STM. Furthermore, the high-pressure reaction kettle is needed for STM, while DESM does not need it. All reaction processes are carried out in open systems, and no need expensive high temperature (>1000℃) sintering furnace, so the DESM is more secure, low-cost.The behavior of temperature-dependence luminescent properties of YAG:Ce3+ phosphors between 6 K and 325 K shows that the luminescent properties are influenced by sintering temperature and environment temperature. As the sintering temperature rising, the impurity phase is gradually disappeared and the crystallinity is increased; surface morphology will become more spherical; luminescent intensity and quantum efficiency are also effectively improved. From the low temperature spectra of YAG:Ce3+ phosphors, we can clearly observe the well-known double band structure of the Ce3+ emission at low environment temperature, that is attributed to the emissions of Ce3+, viz.5d1â†'2F5/2 and 5d1â†'2F7/2. And with the rising of temperature, the two emission bands broaden and start to overlap, resulted in one broad emission band. Meanwhile.the intensity of luminescence is exponential decay, and decrease with the environment temperature rising.Finally, the prospect and the development trend for the YAG:Ce3+ phosphors are also proposed.