Enhanced optical properties and optical temperature sensing performance of SrGa4O7:Bi3+ co-doped with K+ and Cr3+via charge compensation and energy transfer

Abstract

A series of SrGa₄O₇ (SGO)-based phosphors were synthesized via a conventional high-temperature solid-state method. Upon Bi³⁺ ions doping, the phosphors demonstrated an emission spectrum characterized by a peak at 540 nm with a full width at half maximum (FWHM) of 109 nm under 335 nm excitation. To address charge imbalance and enhance the emission intensity of Bi³⁺, strategic incorporation of K⁺ ions as charge compensators was implemented. Notably, the optimal composition SGO:0.02Bi³⁺, 0.02K⁺ achieved a 7.5-fold enhancement in luminescence intensity relative to the singly-doped SGO:0.02Bi³⁺. Comprehensive electron localization function (ELF) calculations elucidated the effect of doping Bi³⁺ and K⁺ ions on the electronic properties of the matrix, validating K⁺ as an efficient charge compensator. Subsequently, energy transfer engineering was realized through co-doping with Cr³⁺ ions, enabling dual-emissive characteristics in both visible (540 nm) and near-infrared (NIR, 765 nm) regions. Capitalizing on the different temperature responses exhibited by Bi³⁺ and Cr³⁺ centers, the SGO:0.02Bi³⁺, 0.02K⁺, 0.01Cr³⁺ phosphor demonstrated good temperature sensing capabilities, attaining a maximum relative sensitivity (S_r) of 1.27% K⁻¹ in the 298–473 K range.