Experimental Evidence for Thermally Enhanced Energy Transfer in Yb3+/Tm3+ Codoped Nanocrystals

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.