Upconversion Luminescence Properties and Temperature Sensing Characteristics of Tm³⁺, Yb³⁺-codoped SrAl₂Si₂O₈ Phosphors with High Thermometric Sensitivities

In this paper, a SrAl 2 Si 2 O 8 :Tm 3+ ,Yb 3+ upconversion (UC) phosphor was prepared with a high-temperature solid-phase method, and proved that the strontium feldspar structure was an excellent UC matrix. The Tm 3+ were shown to have a maximum relative thermometric sensitivity (Sr) of 1.67% K −1 at 298 K and a maximum absolute thermometric sensitivity (Sa) of 1.34% K −1 at 573 K. The non-thermally coupled energy level corresponded to the maximum relative thermometry sensitivity (Sr) of 2.4% K −1 at 298 K and a maximum absolute sensitivity (Sa) of 13% K −1 at 423 K. The use of the fluorescence intensity ratio of the nonthermally coupled energy levels of Tm 3+ for temperature measurements improved the temperature measurement sensitivity of the same material. These results indicated that the phosphor has good temperature sensing performance with a wide sensing range and good stability and has potential thermometry applications in the first biological window.