Extending the optical temperature sensing range of Cr 3+ by synchronously tuning 2 E and 4 T 2 emission.

Due to the different sensitivities of the E and T energy levels of Cr to the local environment, Cr-doped fluorescent materials appear as excellent candidates for highly sensitive temperature sensing based on luminescence intensity ratio technology. However, a way to broaden the strict Boltzmann temperature measuring range is rarely reported. In this work, through Al alloying strategy, a series of SrGaAlO:0.5%Cr( = 0, 2, 4, and 6) solid-solution phosphors were synthesized. Remarkably, the introduction of Al can play a role in regulating the crystal field around Cr and the symmetry of [Ga/AlO] octahedron, realizing the synchronous tuning of E and T energy levels when the temperature changes in a wide range, achieving the purpose of increasing the intensity difference of E → A and T → A transitions, so as to extend the temperature sensing range. Among all samples, SrGaAlO:0.5%Cr showed the widest temperature measuring range from 130 K to 423 K with S of 0.0066 K and S of 1% K@130 K. This work proposed a feasible way to extend the temperature sensing range for transition metal-doped LIR-mode thermometers.