To settle the challenges of optical thermometry with high sensitivity, a series of Tm3+/Yb3+-codoped Y2Mo3O12 (YMO:Tm3+/2xYb3+) submicron particles were developed via a sol–gel route. Excited by 980 nm, bright upconversion (UC) emissions of Tm3+ are observed, in which the optimum intensity is realized when the Yb3+ concentration is 13 mol %. Moreover, the UC mechanism of the emissions originating from the 1G4 level is a three-photon absorption process, while that of the emission from the 3F2,3 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 1G4 level increase and then decrease with raising the temperature, whereas that of the UC emission from the 3F2,3 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 3F2,3 → 3H6 to 1G4 → 3F4 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:Tm3+/2xYb3+ submicron particles can also be manipulated via altering the Yb3+ concentration.

To ameliorate the inherent thermal quenching behaviors of upconverting materials, a series of Ho 3+ /Yb 3+ -codoped Al 2 Mo 3 O 12 (i.e., Al 2 Mo 3 O 12 :Ho 3+ /2xYb 3+ ) microparticles were developed. Upon excitation at 980 nm, intense upconversion (i.e., UC) emissions arising from Ho 3+ are observed, and their optimal states occur at x = 0.09. Besides, the UC mechanisms of these generated emissions from 5 F 4 / 5 S 2 and 5 F 5 levels all pertain to a two-photon absorption process. Furthermore, modified thermal quenching performances are realized in the resultant microparticles, in which the intensities of the UC emissions arising from 5 F 4 / 5 S 2 levels decrease as the temperature increases, while that of the UC emission from the 5 F 5 level increases and then decreases with the increase of temperature. The coexistence of nonradiative transition promoted crossrelaxation, and energy transfer routes can be responsible for the above phenomenon. By studying the diverse UC emission characteristics at high temperatures, we revealed the thermometric properties of Al 2 Mo 3 O 12 :Ho 3+ /2xYb 3+ microparticles, where their sensitivities can be regulated by selecting the spectral mode and dopant contents. According to the intensity ratio of the UC emissions originating from 5 F 5 → 5 I 8 to ( 5 F 4 , 5 S 2 ) → 5 I 7 transitions at different temperatures, one obtains that the relative and absolute sensitivities of the developed compounds reach up to 0.464% and 0.1739 K −1 , respectively. Additionally, by the analysis of the thermochromic performances of final products, their thermometric characteristics were also investigated. Note that the environmental temperature is able to be facilely read out by distinguishing the emitting color. These results verify that the Al 2 Mo 3 O 12 :Ho 3+ /2xYb 3+ microparticles are promising luminescent materials for multimode visual optical thermometry.

For the sake of overcoming the challenges of the optical thermometers with high sensitivity, we designed the Er3+/Yb3+-codoped Y2Mo3O12 microparticles with thermally enhanced upconversion (UC) emissions. Excited at 980 nm,...

To develop high-sensitivity optical thermometers, Yb3+/Tm3+-codoped La2Mo3O12 microparticles were synthesized by the sol–gel method. With the aid of in situ X-ray diffraction, the resultant microparticles are verified to possess negative thermal expansion (NTE) properties. When excited at 980 nm, the upconversion (UC) emission properties of final products are investigated, in which their strongest fluorescence intensities are reached at x = 0.07. Due to the coexistence of the increased energy transfer, cross-relaxation, and nonradiative relaxation procedures, the as-prepared microparticles present thermochromic UC emissions. Moreover, the intensity of UC emission arising from the 3F2,3 excited level at 583 K is 21 times higher than its starting value at 303 K, resulting in thermally enhanced luminescence in resultant microparticles. By employing the fluorescence intensity ratio technique to investigate the temperature-related intensities of UC emissions from 1G4 and 3F2,3 levels, the thermometric characterization of designed compounds is explored, where its highest absolute and relative sensitivities are 0.44 K–1 and 7.37% K–1, respectively. Furthermore, according to the temperature-related lifetimes of 1G4 and 3F2,3 levels of Tm3+, the relative sensitivities of developed microparticles are 0.36% and 0.23% K–1, respectively. Ultimately, visual optical thermometry is also realized by the studied samples owing to their thermochromic UC emissions. Our findings propose a facile strategy by employing NTE to regulate the UC emission behaviors of rare-earth ions so as to obtain high-sensitive luminescent materials.

To meet the needs of contactless optical thermometry, Er3+/Yb3+/Ho3+-tridoped La2Mo3O12 (LMO) microparticles were designed. Excited at 980 nm light, the resultant compounds emit glaring upconversion (UC) emissions and their emitting...