Realization of an Optical Thermometer via Structural Confinement and Energy Transfer

The influence of temperature on a variety of physiological or chemical processes has generated considerable interest, and recently noninvasive lanthanide-incorporated optical thermometers have been considered as promising candidates for monitoring its changes at different scales. Herein, a novel Bi³⁺-activated Sr_3-GdGaO₄₊F_1- phosphor with tunable color has been constructed by a cooperative cation-anion substitution strategy with to the replacement of [Sr²⁺-F^-] by [Gd³⁺-O^2-]. When x = 0, the sample Sr₃GaO₄F/Bi³⁺ possesses a peak wavelength at 438 nm, and this value will shift to 470 nm if x is equal to 1 (Sr₂GdGaO₅/Bi³⁺). In addition, photoluminescence tuning from blue to red has been realized successfully by an efficient Bi³⁺ → Eu³⁺ energy migration model in Sr_2.6Gd_0.4GaO_4.4F_0.6 samples. The specific Bi³⁺ → Eu³⁺ energy transfer has been explained by dipole-dipole interactions derived from a model of the Dexter pathway. Intriguingly, the two dopants (a blue signal from Bi³⁺ and a red signal from Eu³⁺) possess different thermal responses to increasing temperature. Accordingly, the intensity ratio values are sensitive to the temperature changes. The energy level cross relaxation causes the quenching effect of Bi³⁺, and the multi-phonon de-excitation mode leads to the thermal quenching of Eu³⁺. At room temperature (298 K), the determined maximum relative sensitivity (S_r) is 1.27% K^-1. Moreover, the absolute sensitivity (S_a) is 0.067 K^-1 since the temperature is elevated to 523 K. The collected results are superior to most of the reported optical thermometry materials.