Thermochromic Upconversion Emission in Tm³⁺/Yb³⁺-Codoped La₂Mo₃O₁₂ Microparticles via Negative Thermal Expansion Engineering for Ultrahigh Sensitivity Optical Thermometry

Abstract

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.

Manipulating the thermometric behaviors of Er3+/Yb3+/Ho3+-tridoped La2Mo3O12 polychromatic upconverting microparticles via adjusting spatial mode and a sensing strategy

“…S2(a) (ESI †). On the other hand, the optical energy band gap (E g ) values of the studied samples can be estimated from the diffuse reflectance spectra, as defined below: 29,32…”

“…S2(a) (ESI†). On the other hand, the optical energy band gap ( E g ) values of the studied samples can be estimated from the diffuse reflectance spectra, as defined below: 29,32 αhv = A ( hv − E g ) n [ hvF ( R )] 1/ n = B ( hv − E g )where α and F ( R ) are the absorption parameters, hv is the phonon energy, A and B are the constants, R represents the reflection coefficient, and the n value determines the semiconductor category. 28,31 Herein, the n value of LMO is 1/2 so it is an indirect semiconductor.…”

“…27 In spite of these exciting achievements, extra investigations are still needed to further carry out the luminescence characterization of rare-earth ion-doped molybdates so as to promote their applications. Currently, the interest in La 2 Mo 3 O 12 (LMO) is increasing and various rareearth ions, such as Tm 3+ , Eu 3+ , Er 3+ , Sm 3+ , etc., [28][29][30] have been introduced into LMO host lattices to synthesize highly efficient luminescent materials. However, as far as we know, there are no studies on the luminescence and thermometric properties of Er 3+ / Yb 3+ /Ho 3+ -tridoped LMO microparticles.…”

“…Currently, the interest in La 2 Mo 3 O 12 (LMO) is increasing and various rare-earth ions, such as Tm 3+ , Eu 3+ , Er 3+ , Sm 3+ , etc. , 28–30 have been introduced into LMO host lattices to synthesize highly efficient luminescent materials. However, as far as we know, there are no studies on the luminescence and thermometric properties of Er 3+ /Yb 3+ /Ho 3+ -tridoped LMO microparticles.…”

Dy3+-Assisted Negative-Thermal Quenching in Ho3+-Doped SrMoO4 for Luminescence Thermometry and Lighting Applications

“…Significant efforts have been made to explore and design novel Ln 3+ -doped inorganic phosphors as potential thermal probes due to their numerous advantages, such as excellent luminescence properties, low toxicity, superior thermal and chemical stability, and narrow bandwidth. – The SrMoO 4 phosphor as a host is an excellent host for Ln 3+ ions as it allows efficient and simultaneous energy transfer from the ligand to metal charge transfer (LMCT) band to the energy levels of the doped rare-earth ions. , Therefore, it is feasible to get a good emission corresponding to the two rare-earth ions with host excitation. We have utilized this property of the SrMoO 4 phosphor for dual-mode FIR thermometry.…”