The luminescence thermometer based on up-converting NaGdF4:Yb3+,Er3+@ZIF-8 nanoparticles

An upconversion luminescence nanothermometer based on NaGdF₄:Yb³⁺,Er³⁺@ZIF-8 nanoparticles, with an average size of approximately 289.5 nm and a polydispersity index of 24.85 %, was successfully synthesized via a hydrothermal route. The as-synthesized NaGdF₄:Yb³⁺,Er³⁺@ZIF-8 nanoparticles exhibit upconversion luminescence in both the visible and near-infrared regions under excitation within the first and second biological windows (NIR-I and NIR-II). Moreover, excitation in the NIR-I and NIR-II regions can be utilized to modulate the upconversion and downshifting emission of the NaGdF₄:Yb³⁺,Er³⁺@ZIF-8 nanoparticles. Temperature-dependent upconversion luminescence measurements revealed a satisfactory thermal response over a wide temperature range of 83–743 K. The maximum relative sensitivity achieved was 3.08 % K⁻¹ at 123 K, which is 5.1 times higher than that of the bare core α-NaGdF₄:Yb³⁺,Er³⁺ nanoparticles. The UV-VIS spectrum further confirmed the presence of the specific bonds of imidazole compounds on the synthesized core/shell NaGdF₄:Yb³⁺,Er³⁺@ZIF-8. Additionally, TEM/HRTEM images and SAED patterns recorded at different locations verified the presence of ZIF-8 shell layers on the surface of the α-NaGdF₄:Yb³⁺,Er³⁺ core nanoparticles.