实验研究了从体材料到纳米晶(NCs)系统中涉及大能隙(5800 cm-1)的多声子弛豫(MR)。在MR非线性理论框架下,用单频近似声子谱分析了β-NaGdF4：Tb3+NCs中Tb3+：5 D3→5 D4的MR速率与温度的关系。在12~312 K范围内,实验数据与理论曲线符合得很好。结果表明,MR的产生主要是能量较大的光学声子起作用。在Rayleigh极限下,假设Tb3+发射体位于一个纳米球的中心,使用Green张量方法计算了自发衰减速率Гrad。在纳米球内没有发现局域态密度( LDOS)的明显改变。然而,当R<35 nm时,在Chew理论的基础上获得在球外LDOS的一个新的高斯分布。%This paper reports the experimental study of multiphonon relaxation(MR)involving a large energy gap(5800cm-1)crossover from bulk to nanocrystal(NC) system. The temperature dependence of MR rate for 5 D3→5 D4 of Tb3+ in β-NaGdF4: Tb3+ NCs was analyzed in a single-frequency approximation of phonon spectrum in the framework of the nonlinear theory of MR. The experimental data well agree with the theoretical curves within the range of 12 K to 312 K. It is shown that MR occurs predominantly via high-energy optical phonons. In Rayleigh limit, assuming that the Tb3+ emitter was located at the center of a nanosphere, the spontaneous decay rate Γrad was calculated using Green tensor approach. No significant variation in the local density of states(LDOS) was found inside the nanospheres. However, for R<35 nm, a new Gaussian distribution of LDOS was obtained based on Chew's theory outside the nanospheres.
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