Extending the optical temperature sensing range of Cr³⁺ by synchronously tuning ²E and ⁴T₂ emission

Due to the different sensitivities of the E-2 and T-4(2) energy levels of Cr3+ to the local environment, Cr3+-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 Al3+ alloying strategy, a series of SrGa12-xAlxO19:0.5%Cr3+(x = 0, 2, 4, and 6) solid-solution phosphors were synthesized. Remarkably, the introduction of Al3+ can play a role in regulating the crystal field around Cr3+ and the symmetry of [Ga/AlO6] octahedron, realizing the synchronous tuning of E-2 and T-4(2) energy levels when the temperature changes in a wide range, achieving the purpose of increasing the intensity difference of E-2 -> (4)A(2) and T-4(2) -> (4)A(2) transitions, so as to extend the temperature sensing range. Among all samples, SrGa6Al6O19:0.5%Cr3+ 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.