Towards ultra-sensitive multimodal luminescent thermometers enabled by high crystal field strength of Lu2CaMg2Ge3O12:Yb3+,Nd3+,Er3+ phosphors

Abstract

The exploration of acquiring excellent thermal performance of luminescence thermometers has become a key focus, owing to their non-contact measurement, high spatial resolution and rapid response. However, many luminescence thermometers still suffer from unsatisfactory relative sensitivity and a single temperature sensing mode. Herein, we report a Lu₂CaMg₂Ge₃O₁₂ garnet structure oxide with a stronger crystal field for ultra-sensitive and multimodal luminescence intensity ratio (LIR) optical thermometry based on the thermally coupled levels (TCLs) of Nd³⁺ (⁴F_7/2 and ⁴F_3/2) and Er³⁺ (²H_11/2 and ⁴S_3/2), where the relative sensitivity (S_r) can be up to 2.62% K⁻¹ and 1.15% K⁻¹, respectively. Furthermore, the energy level splitting factor K_e, which is used to quantify the energy level splitting extent of the doped ions, is estimated with the help of the dielectric chemical bond theory of complex crystals. As a result of the strong crystal field, the near-infrared (NIR) light-responsive temperature sensing performance of Er³⁺ (⁴I_13/2) is enabled by the Stark sublevels with the relative sensitivity value of 0.46% K⁻¹. This work not only provides a fresh perspective for developing optical thermometers with outstanding temperature performance, but also provides inspiration for pursuing a multimodal luminescence thermometer.