Tailoring of Upconversion Emission in Tm 3+ /Yb 3+ -Codoped Y 2 Mo 3 O 12 Submicron Particles Via Thermal Stimulation Engineering for Non-invasive Thermometry

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To settle the challenges of optical thermometry with high sensitivity, a series of Tm 3+ /Yb 3+ -codoped Y 2 Mo 3 O 12 (YMO:Tm 3+ /2 x Yb 3+ ) submicron particles were developed via a sol–gel route. Excited by 980 nm, bright upconversion (UC) emissions of Tm 3+ are observed, in which the optimum intensity is realized when the Yb 3+ concentration is 13 mol %. Moreover, the UC mechanism of the emissions originating from the 1 G 4 level is a three-photon absorption process, while that of the emission from the 3 F 2,3 level is a two-photon absorption process. Furthermore, thermally enhanced emission intensities are realized in the studied compounds due to the negative thermal expansion effect. Notably, owing to the coexistence of improved energy transfer and cross-relaxation processes at elevated temperature, the intensities of the UC emissions from the 1 G 4 level increase and then decrease with raising the temperature, whereas that of the UC emission from the 3 F 2,3 level is enhanced monotonously as temperature increases. Via analyzing the inconsistent thermal quenching characteristics of the UC emissions, we explored the thermometric behaviors of the synthesized products and found that their sensitivities are dependent on the spectral mode. Through investigating the dependence of the emission intensity rate of the emissions from 3 F 2,3 → 3 H 6 to 1 G 4 → 3 F 4 transitions on temperature, one knows that the maximum absolute and relative sensitivities of the resultant submicron particles are 0.198 K –1 and 3.27% K –1, respectively. Additionally, the thermometric behaviors of YMO:Tm 3+ /2 x Yb 3+ submicron particles can also be manipulated via altering the Yb 3+ concentration.