Experimental Evidence for Thermally Enhanced Energy Transfer in Yb<sup>3+</sup>/Tm<sup>3+</sup> Codoped Nanocrystals
Yinghao Wei, Sen Yang, Kaihang Zhu, Linshuo Gao, Liji Wang, Guanying Chen, Ai‐Hua Li
Abstract
Abstract Weak luminescence of the small‐sized lanthanide‐doped nanoparticles has limited their applications long. In recent years, there is a growing interest in luminescence thermal enhancement in small‐sized upconversion nanoparticles (UCNPs). The mitigation of surface quenching effects and the improvement of energy transfer (ET) are two convincing explanations for this phenomenon. A systematical investigation on the luminescence dynamics of Yb 3+ is implemented. ET rate and then the proportion of ET increases greatly with rising temperatures in Yb 3+ /Tm 3+ codoped system, while an alternative trend can be summarized in Yb 3+ /Er 3+ one. Based on these findings, therefore it can be concluded that the surface quenching mitigation related to the desorption of water molecules on the surface is a common mechanism of the luminescence thermal enhancement. But ET related to the thermally‐activated surface phonons is a special case, it does play a positive role in Yb 3+ /Tm 3+ system. These findings not only explain the upconversion luminescence thermal enhancement in Yb 3+ /Tm 3+ system is more significant but also help to understand thermal enhancement and benefit highly‐sensitive temperature probe design.