Double-excited states of charge transfer band and 4f-4f in single-phase K₃Gd(VO₄)₂:Tb³⁺/Sm³⁺ phosphors with superior sensing sensitivity for potential luminescent thermometers

Temperature is one of the fundamental parameters for thermodynamics and its accurate detection is necessary. The novel strategy of luminescent materials based on the fluorescence intensity ratio technique has been promised for thermometers in more practical environments to overcome the drawbacks of conventional thermometers in recent. Herein, the novel single-phase K₃Gd(VO₄)₂:Tb³⁺/Sm³⁺ phosphors were successfully prepared, and the ⁴G_5/2 → ⁶H_9/2 (Sm³⁺) and ⁵D₄ → ⁷F₅ (Tb³⁺) transitions could be promised for luminescent thermometers. Besides, under the double-excited states of charge transfer band (CTB, 317 nm) and 4f-4f (478 nm) excitations, the K₃Gd(VO₄)₂:Tb³⁺/Sm³⁺ phosphors exhibited different concentration quenching mechanisms in energy transfer processes and also showed superior absolute sensing sensitivity (S_a) and relative sensing sensitivity (S_r). Especially, the maximum S_a and S_r values reached up to 0.568 K⁻¹ and 11.24% K⁻¹, respectively and the temperature resolution of the KGV:0.2Tb³⁺/0.01Sm³⁺ phosphor was higher than 0.004 K under the excitation wavelength of CTB (317 nm), indicating that the double-excited states in the single-phase KGV:Tb³⁺/Sm³⁺ phosphors with superior sensing sensitivity could be a novel candidate for potential optical thermometers.