白光LED固态照明光转换荧光体

报道了当前热点固态照明白光LED对所用光转换荧光体的特殊要求,从发光学和晶场理论出发,提出研发白光LED用荧光体的几种方案和原则.依据多年成果,特别阐述在稀土铝镓石榴石体系,氯硅酸钙及某些钨钼酸盐中,Ce³⁺、Pr³⁺、Tb³⁺、Eu³⁺、Eu²⁺及Mn²⁺离子的发光特性,能量传递,Eu²⁺的特征“阶梯状”光谱以及激活剂在晶体中所占据不同晶体学格位与发光性质的关联性.这些材料都可用于白光LED之中.实践证明,这些基础性研究和原理是研制白光LED用荧光体的基础.光转换荧光体与InGaN蓝光芯片结合可以获得符合严格标准的全色温(2700~8000K)的高显色性白光LED光源.白光LED及InGaN蓝光LED的光电性能与正向电流I_F密切相关,器件散热极为重要.提出的在不同I_F下,LED的相关色温差(ρT_c)可用来表征LED色温变化幅度及稳定性.

Phosphors for White LED Solid State Lighting

White light-emitting diode(LED)is rapidly evolving for use in the special and general illumination applications. A main method for producing white LED is to utilize a InGaN blue or near UV LED chip and phosphors which have the characteristic of wavelength-conversion.The essentials of phosphors which are sui-table for white LED include: (1)phosphors are efficiently excited by blue or NUV LED and efficient radiative emission of appropriate visible wavelength; (2)excellent preformence of temperature quenching; (3)good stability and (4)small particle size(≤5nm). In this paper, the schemes and principles on advanced phosphors for white LED are discussed in great detail. It is important that a relationship between the 5d centroid shift in Eu²⁺ and Ce³⁺ ions, anion polarizability, covalency, electronegativity of the cations, perturbations of the crystalline environment in phosphor hosts, as P.Dorents's results. Based on our studies, luminescence properties and energy transfer of Ce³⁺,Pr³⁺,Tb³⁺,Eu³⁺,Eu²⁺ and Mn²⁺ ions are presented in the (Y,Gd)₃(Al,Ga)₅O₁₂ garnet and Ca₈A(SiO₄)₄Cl₂ (A=Mg,Zn)chlorosilicate systems and some tungstate and molybdate. The staircase spectrum in Eu²⁺4f⁶(⁷F_J)5d configuration was observed in chlrosilicate phosphors at RT. The purish-blue(Ce³⁺), green(Eu²⁺,Mn²⁺) and red(Eu³⁺)emission bands arise from Ce³⁺,Eu²⁺,Mn²⁺ ions locating at eight-, six-and four-coordinated inequivalent sites in chlorosilicate, respectively. White LEDs which show the related color temperature in the range of 2700~8000K and high rending index (R_a) are obtained by combining InGaN blue chip and phosphors. The emission spectrum, chromaticity coordinate (x,y),luminous flux and luminous efficiency of white LED packaged by us were reported. The optic characteristic changes at various forward-bias currents(I_F)have been discussed. In this study, it was shown that chromaticity coordinate values (x and y) of white LED shifted and resulted in the related color temperature (T_c) increase. The T_c change and stability on a white LED can been characterized by a difference valure (ρT_c) of related color temperature at various I_F. High power and high brightness white LED is the future of solid state lighting. New efficient phosphors for SSL will be developed.