Tailoring of Upconversion Emission in Tm³⁺/Yb³⁺-Codoped Y₂Mo₃O₁₂ Submicron Particles Via Thermal Stimulation Engineering for Non-invasive Thermometry

Abstract

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.

Manipulating Upconversion Emission and Thermochromic Properties of Ho3+/Yb3+-Codoped Al2Mo3O12 Microparticles by Negative Lattice Expansion for Multimode Visual Optical Thermometry

“…37 Notably, these three bands all originate from the water molecules absorbed on the surface of the synthesized microparticles. Furthermore, the other two peaks at 869 and 489 cm −1 are associated with the stretching vibration modes of Mo−O−Mo and Mo−O, 11 respectively.…”

“…As we know, the relation between the UC emission intensity (i.e., I) and pump power (i.e., P) is able to be expressed as: I ∝ P n or log(I) ∝ n log(P), where n represents the number of photons adopted to form the desired levels. 11,42 The plots of log(I) versus Afterward, ET from Yb 3+ to Ho 3+ occurs, resulting in the formation of the 5 I 6 level. Note that the 5 I 6 level is able to pump to the higher level of 5 F 4 / 5 S 2 via the second ET process, as depicted in Figure 3f.…”

“…Thereby, the repeatability of I 661 /I 545 and I 661 /I 760 combinations is decided to be 98.05 and 99.04%, respectively, further revealing that the prepared microparticles have excellent reversibility. On the other hand, the temperature uncertainty (i.e., ΔT) of optical thermometers is also an important parameter to indicate their temperature sensing performance, which can be estimated by the use of the following expressions 11,49 T S…”

“…However, they usually exhibited unsatisfied sensitivities because of the small energy band separation (i.e., 200−2000 cm −1 ) of TCLs. 11,12 Thereby, some novel routes are required to be put forward so as to settle this shortage.…”

“…Although contact temperature gauges (i.e., thermocouples and liquid-filled glass thermometers) have been widely used in our daily life, noncontact luminescent temperature sensing technology has drawn considerable attention because of its splendid advantages including fast response, high sensitivity, nonintrusion, and so forth. − In the case of noncontact optical thermometry, the fluorescence intensity ratio (i.e., FIR) method was adopted to explore the fluorescence intensities of two thermally coupled levels (i.e., TCLs) of rare-earth ions at various temperatures. , By applying this strategy, lots of optical thermometers based on rare-earth ion-doped luminescence materials, such as YVO 4 :Tm 3+ /Yb 3+ , Y 4 GeO 8 :Er 3+ /Yb 3+ , Gd 9.33 (SiO 4 ) 6 O 2 :Ho 3+ /Yb 3+ , LiBaPO 4 :Nd 3+ , and La 2 Mo 2 O 9 :RE 3+ /Yb 3+ (RE 3+ = Tm 3+ , Er 3+ , Ho 3+ ), − had been proposed. However, they usually exhibited unsatisfied sensitivities because of the small energy band separation (i.e., 200–2000 cm –1 ) of TCLs. , Thereby, some novel routes are required to be put forward so as to settle this shortage.…”