A novel optical temperature sensor and energy transfer properties based on Tb³⁺/Sm³⁺ codoped SrY₂(MoO₄)₄ phosphors

A series of SrY₂(MoO₄)₄ phosphors doped and co-doped with Tb³⁺/Sm³⁺ ions was synthesized to develop new optical temperature sensor materials. The structures, morphologies, and luminescent characteristics of these phosphors were thoroughly investigated. Luminescence spectra of mono-doped SrY₂(MoO₄)₄ phosphors were measured under the excitation at 375 and 403 nm corresponding to direct excitation of Tb³⁺ and Sm³⁺, respectively. The characteristic luminescence bands corresponding to electronic transitions of terbium and samarium ions were detected and investigated for different dopant concentrations. The emission spectrum of the Tb³⁺/Sm³⁺ co-doped sample exhibited a total of five distinct emission peaks, indicating an energy transfer from Tb³⁺ to Sm³⁺ ions. The energy transfer efficiency from Tb³⁺ ions to Sm³⁺ ions was investigated in detail. At elevated temperatures, Tb³⁺ and Sm³⁺ exhibited distinct thermal sensitivities in their emission and excitation spectra, leading to evident thermochromic behavior. The fluorescence intensity ratio (FIR) was utilized with dual center to evaluate the temperature sensitivity of SrY₂(MoO₄)₄:Tb³⁺/Sm³⁺ phosphors. The temperature sensing mechanism relied on the emission band intensity ratios of the ⁴G_5/2 → ⁶H_5/2, ⁴G_5/2 → ⁶H_9/2, and ⁴G_5/2 → ⁶H_7/2 transitions of Sm³⁺ in conjunction with the ⁵D_5/2 → ⁷F_5/2 transitions of Tb³⁺. This approach demonstrated high thermal sensitivity values, reaching up to 0.9% K^-1. The studied nanoparticles exhibited sub-degree thermal resolution, making them suitable candidates for precise temperature-sensing applications.