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

Abstract

To meet the needs of contactless optical thermometry, Er³⁺/Yb³⁺/Ho³⁺-tridoped La₂Mo₃O₁₂ (LMO) microparticles were designed and synthesized. Upon exciting with 980 nm light, the synthesized compounds emit glaring upconversion (UC) emissions and their emission colors can be tuned from green to yellow by altering the Ho³⁺ content. It is found that the optimal doping contents for Yb³⁺ and Ho³⁺ in LMO are 9 and 1 mol%, respectively, and the UC emission mechanism involved is a two-photon harvest process. Using the fluorescence intensity ratio (FIR) technique to analyze the temperature responses of the UC emissions arising from thermally coupled levels (TCLs) and non-thermally coupled levels (non-TCLs), the temperature sensing abilities of the synthesized samples were investigated. When the TCLs of Er³⁺ (²H_11/2, ⁴S_3/2) are used, the synthesized microparticles present the highest absolute and relative sensitivities of 0.0085 and 1.0236% K⁻¹, respectively. Moreover, when the non-TCLs of Er³⁺ (²H_11/2) and Ho³⁺ (⁵F₅) are used, the maximum absolute and relative sensitivities of the synthesized compounds are 0.0296 and 0.6287% K⁻¹, respectively. Clearly, the thermometric characteristics of the final products can be regulated via using different sensing strategies (i.e., TCLs and non-TCLs) and emission combinations (i.e., spatial mode). However, the change of the Ho³⁺ content has little impact on the temperature sensing capacity of the synthesized products. These results indicate that Er³⁺/Yb³⁺/Ho³⁺-tridoped LMO microparticles are promising candidates for optical thermometers and our findings also provide possible strategies for regulating the thermometric properties of rare-earth ion doped luminescent materials.