Enhanced Thermal Stability and Energy Transfer by Crystal‐Field Engineering in a Garnet Phosphor for Thermometry and NIR‐LED

Abstract It is of significant importance to tailor the luminescent properties of Cr³⁺ ions as efficient near‐infrared (NIR) emitter for extended optical applications. Here, crystal field engineering is explored to tailor the luminescent properties of a Cr³⁺‐doped garnet, Lu₂Ca_{1 ‐ x}Sr_xAl₄SiO₁₂ (x = 0–1). As Ca²⁺ is substituted by Sr²⁺, the emission of Cr³⁺ becomes sharper with longer lifetime, indicating that the ²E_g→⁴A_2g transition becomes dominant. More importantly, the thermal stability is greatly improved, as the emission intensity at 480 K increases from 83% to 111% of that at 300 K. Moreover, the efficiency of the energy transfer from the Cr³⁺ to Yb³⁺/Nd³⁺ increases from 60–70% to 80–90%. The intensity ratio of I₈₁₀/I₇₀₆ from the Lu₂SrAl₄SiO₁₂:Cr³⁺,Nd³⁺ can be applied to thermometry, with the maximum relative sensitivity value of 1.43% K^–1 at 303 K. Compared with the blue emission from light‐emitting diode (LED) chip, a clearer and more accurate imaging is established with NIR emission from Cr³⁺. Furthermore, the intensity ratio of the emissions from the Cr³⁺ and Yb³⁺ ions is applied to differentiate pork, chicken, and beef. These findings provide an avenue to optimize the thermal stability and energy transfer of Cr³⁺‐activated NIR emitters for the applications in thermometry and NIR‐LED.