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 Sr3-xGdxGaO4+xF1-x phosphor with tunable color has been constructed by a cooperative cation-anion substitution strategy with to the replacement of [Sr2+-F-] by [Gd3+-O2-]. 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 Sr2.6Gd0.4GaO4.4F0.6 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 (Sr) is 1.27% K-1. Moreover, the absolute sensitivity (Sa) 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.