Improving luminescence thermometry based on non-thermally coupled levels of double luminescent ionic centers Tm3+ and Ho3+ in NaYF4:Yb/Tm@NaYF4:Yb/Ho microcrystals

Abstract

Luminescence thermometry has recently been gaining popularity in science and technology fields. However, most reported works have used the fluorescence intensity ratio (FIR) to obtain the temperature based on thermally coupled energy levels (TCLs), which have hindered the sensitivity of the technique and limited its applications. Here, NaYF₄:Yb/Tm@NaYF₄:Yb/Ho microcrystals were prepared using a hydrothermal method. Based on the non-thermally coupled energy levels (NTCLs) of the double luminescent ionic centers Tm³⁺ and Ho³⁺, the materials exhibited temperature-dependent luminescence in the range of 304 K to 574 K. The maximum sensitivities were found to be S_a = 0.135 K⁻¹ at 574 K and S_r = 1.101% K⁻¹ at 484 K based on red (Tm³⁺) and green (Ho³⁺) emission bands. This study has provided a promising new strategy to break the TCL restriction and has shown the material to have potential applications in luminescence thermometry.