Thulium cross-relaxation in a low phonon energy crystalline host
Thulium cross-relaxation in a low phonon energy crystalline host
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DOI：
10.1103/physrevb.66.245101
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发表时间：
2002-12-15
影响因子：
3.7
通讯作者：
Bowman, SR
中科院分区：
文献类型：
--
作者：
Ganem, J;Crawford, J;Bowman, SR
我们报道了Tm3+在低声子能量氯化物基质中的交叉弛豫。在浓度为0.7~7×10(20)ion/cm(3)的YCl3晶体中，在300~500K温度范围内研究了Tm3+在基质YCl3中的交叉弛豫随温度和浓度的变化关系。采用自晶种垂直布里奇曼法从无水YCl3和TmCl3粉末熔体中生长晶体。收集并分析了三种不同Tm~(3+)浓度的晶体在1100-2000 nm光谱区的荧光光谱和寿命。每个荧光光谱都包含以1200、1490和1800 nm为中心的三个主要特征，它们反映了Tm3+的前三个激发能级的布居。根据荧光寿命数据确定了多声子弛豫和交叉弛豫的速率。随着温度的升高，1200 nm荧光的增加是吸热交叉驰豫过程的证据。这表明了一种全新的光学冷却机制。由声子辅助能量转移理论给出的宏观速率方程模型与光谱数据符合得很好。
We report on the cross-relaxation of Tm3+ in a low phonon energy chloride host. The temperature and concentration dependence for Tm3+ cross-relaxation in the host YCl3 was studied between 300 and 500 K, in crystals of YCl3 with concentrations ranging from 0.7 to 7x10(20) ions/cm(3). Crystals were grown from melts of anhydrous YCl3 and TmCl3 powders under Cl-2 atmosphere using a self-seeded vertical Bridgeman technique. Fluorescence spectra and lifetimes resulting from quasi-cw pumping with a 0.5-W, 811-nm diode were collected and analyzed for the spectral region 1100-2000 nm versus temperature for three crystals with varying Tm3+ densities. Each of the fluorescence spectra contain three broad features centered at 1200, 1490, and 1800 nm that reflect the populations of the first three excited levels of Tm3+. Rates for multiphonon relaxation and cross-relaxation were determined from the fluorescence lifetime data. An increase in 1200-nm fluorescence as the temperature rises is evidence of an endothermic cross-relaxation process. This suggests a fundamentally new mechanism for optical cooling. A macroscopic rate equation model with its temperature and concentration dependence given by theories for phonon-assisted energy transfer is fit to the spectral data.