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 2 E and 4 T 2 energy levels of Cr 3+ to the local environment, Cr 3+ -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 3+ alloying strategy, a series of SrGa 12- x Al x O 19 :0.5%Cr 3+ ( x = 0, 2, 4, and 6) solid-solution phosphors were synthesized. Remarkably, the introduction of Al 3+ can play a role in regulating the crystal field around Cr 3+ and the symmetry of [Ga/AlO 6 ] octahedron, realizing the synchronous tuning of 2 E and 4 T 2 energy levels when the temperature changes in a wide range, achieving the purpose of increasing the intensity difference of 2 E → 4 A 2 and 4 T 2 → 4 A 2 transitions, so as to extend the temperature sensing range. Among all samples, SrGa 6 Al 6 O 19 :0.5%Cr 3+ showed the widest temperature measuring range from 130 K to 423 K with S a of 0.0066 K -1 and S r of 1% K -1 @130 K. This work proposed a feasible way to extend the temperature sensing range for transition metal-doped LIR-mode thermometers.