Comparison study on the different strategies designed for ratiometric luminescence thermometry in Er3+/Yb3+: SrMoO4 phosphor

Abstract

To validate the feasibility of the strategy designed for ratiometric luminescence thermometry, the impacts of doping concentration and power density on the thermometric parameter and measurement result should be assessed but have normally been discounted. Herein, Yb3+/Er3+: SrMoO4 upconverting (UC) phosphors were prepared via a hydrothermal method. The UC luminescence spectra were composed of the strong green emission and weak red emission bands upon 980 nm excitation. The thermally coupled levels (TCLs) of Er3+: 2H11/2, 4S3/2 and the non-thermally coupled levels (non-TCLs) of Er3+: 2H11/2, 4F9/2 were selected for fluorescence intensity ratio (FIR) thermometry, while the emissions originating from 4S3/2 Stark sublevels to 4I15/2 ground level were adopted for the valley to peak ratio (VPR) thermometry. The dependences of FIR-TCL (I535/I558), FIR-non-TCL (I535/I663) and VPR (I553/I558) values on the doping concentration and pump power density were analyzed. The results showed that the FIR-non-TCL and VPR data suffered from the interferences from the fluctuations in doping concentration and power density, causing the unavoidable measuring errors and unstable thermometric performance. Such problems could be solved by utilizing the concentration-insensitive and power-insensitive FIR-TCL, which also gained the high relative sensing sensitivity with the optimal value of 1.18% K-1. This work will provide guidance on choosing the appropriate strategy for the reliable luminescence thermometry.