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

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, Lu2Ca1 ‐ xSrxAl4SiO12 (x = 0–1). As Ca2+ is substituted by Sr2+, the emission of Cr3+ becomes sharper with longer lifetime, indicating that the 2Eg→4A2g 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.