Dual-emission center ratiometric optical thermometer based on Bi³⁺ and Mn⁴⁺ co-doped SrGd₂Al₂O₇ phosphor

In recent years, more and more attention has been paid to optical temperature sensing, and how to improve its accuracy is the most important issue. Herein, a new temperature sensing material, SrGd₂Al₂O₇:Bi³⁺,Mn⁴⁺, based on fluorescence intensity ratio was designed in this work. It has both blue-purple and red luminescence under 300 nm excitation, and the dual-emitting centers with distinct colors, the different thermal sensitivities of Bi³⁺ and Mn⁴⁺, and the energy transfer between Bi³⁺ and Mn⁴⁺ give it excellent signal resolution and accurate temperature detection. The S_a of SrGd₂Al₂O₇:0.04Bi³⁺,0.003Mn⁴⁺ phosphor reaches a maximum value of 8.573% K^-1 at 473 K, and the corresponding S_r is 1.927% K^-1, both of which are significantly better than those of most other reported optical temperature sensing materials. Taking all the results into account, the SrGd₂Al₂O₇:0.04Bi³⁺,0.003Mn⁴⁺ phosphor can be regarded as a prominent FIR-type temperature sensing material.