Wang Junbei, Zhou Xianju, Xiang Guotao, Jiang Sha, Li Li, Wang Yongjie, Li Yanhong, Jing Chuan, Yao Lu, Yang Hongmei, Huang Yanhao, Wang Feng
School of Science, Chongqing University of Posts and Telecommunications, Chongqing, 400065, P. R. China.
School of Materials Science and Engineering, Chongqing Jiaotong University, Chongqing, 400065, P. R. China.
Dalton Trans. 2022 Nov 21;51(45):17224-17234. doi: 10.1039/d2dt02744e.
Because of thermal quenching, conventional luminescent materials suffer from severe problems when employed at high temperatures. Based on the thermally coupled energy levels (TCLs) of rare-earth ions, we report and explain an abnormal thermal quenching phenomenon in the excited state of the charge transfer band (CTB), which is expected to bring out a solution to the problems of the low sensitivity of temperature-sensing materials and applications at high temperature. Temperature-dependent excitation spectra of Er or Eu-doped CaMoO, CaWO, and LuVO phosphors are recorded. It was found that CTB exhibited two abnormal thermal quenching phenomena. One is that the intensity of the whole CTB increases with the rising temperature, named totally abnormal thermal quenching (TATQ), and the other is the integrated intensity decrease but the edge of the CTB at longer wavelengths enhanced with temperature, named edge abnormal thermal quenching (EATQ). The temperature-dependent excitation and diffuse reflectance spectra of the host and rare earth ions with moderate (Er) and large (Eu) energy separation between TCLs are investigated. One photodynamic model, considering influential factors, such as the absorption of the phosphor, energy transfer efficiency between CTB and dopants, and thermal coupling effect, is proposed and explains the unusual thermal response of CTB. Luminescence thermometry based on the abnormal thermal quenching is realized with the obtained relative sensitivity of 4.65% K @ 328 K, which is four times the value derived from the classic TCLs in the same phosphor.
由于热猝灭，传统发光材料在高温下使用时会面临严重问题。基于稀土离子的热耦合能级（TCLs），我们报道并解释了电荷转移带（CTB）激发态下的一种异常热猝灭现象，有望为解决温度传感材料灵敏度低以及高温应用的问题提供一种解决方案。记录了掺铒或铕的钼酸钙、钨酸钙和钒酸镥荧光粉的温度依赖激发光谱。发现CTB表现出两种异常热猝灭现象。一种是整个CTB的强度随温度升高而增加，称为完全异常热猝灭（TATQ），另一种是积分强度降低，但CTB在较长波长处的边缘随温度增强，称为边缘异常热猝灭（EATQ）。研究了TCLs之间具有中等（铒）和大（铕）能量间隔的主体和稀土离子的温度依赖激发光谱和漫反射光谱。提出了一个光动力学模型，考虑了荧光粉的吸收、CTB与掺杂剂之间的能量转移效率以及热耦合效应等影响因素，并解释了CTB异常的热响应。基于异常热猝灭实现了发光测温，在328 K时获得的相对灵敏度为4.65% K，是同一荧光粉中经典TCLs得出值的四倍。
