Dual-mode luminescent core-shell nanoarchitectures for highly sensitive optical nanothermometry

Currently, FIR-based luminescent nanothermometry has aroused wide concern for its promising applications in fast-moving objects, harsh environments and microscopic temperature. Synchronously promoting the absolute and relative sensitivities of optical thermometers is one of the significant issues at present. In this work, a new nanothermometry strategy to possess both high absolute and relative sensitivities have been proposed by coupling of thermally-coupled-levels-based technique with non-thermally-coupled-levels method in the core-shell designed nanomaterials . Following this strategy, the core-shell-structured NaGdF 4 :Yb,Er@ NaYF 4 :Ce,Tb,Eu nanocrystals have been successfully prepared. Remarkably, the adverse cross-relaxation among different activators is extremely suppressed owing to the spatial separation of Er 3+ and Eu 3+ ,Tb 3+ activators, being conducive to the realization of both intense green upconverting emissions and yellow downshifting luminescence. Moreover, the temperature-sensitive dual-mode luminescent behaviors of core-shell nanomaterials are systematically studied to probe the possible application in FIR-related luminescent thermometry. Specially, the thermally-coupled-levels-based FIR of Er 3+ : 2 H 11/2  →  4 I 15/2 transition to Er 3+ : 4 S 3/2  →  4 I 15/2 one and non-thermally-coupled-levels-based FIR of Eu 3+ : 5 D 0 → 7 F 2 transition to Tb 3+ : 5 D 4 → 7 F 6 one are proved to be applicable as temperature probes, leading to the achievement of dual-mode temperature sensing. Using the pre-designed core@shell nanoarchitectures, the absolute sensitivity can reach up to 1.02% K −1 based on Eu 3+ ,Tb 3+ Stokes emissions and the relative sensitivity could reach as high as 1.12% K −1 based on Er 3+ anti-Stokes luminescence. We believe that this study provides a valid approach for developing high-performance optical nanothermometers.