α-NaYb(Mn)F4:Er3+/Tm3+@NaYF4 UCNPs as Band-Shape Luminescent Nanothermometers over a Wide Temperature Range

Novel flower-like alpha-NaYb(Mn)F-4:Er3+/Tm3+@NaYF4 upconversion nanoparticles (UCNPs) as luminescent nanothermometers have been developed by combining liquid-solid solution hydrothermal strategy with thermal decomposition strategy. Under 980 nm excitation, they exhibit intense upconversion luminescence and temperature-dependent upconversion luminescence over a wide temperature range. The influence of temperature on band-shape upconversion luminescence (UCL) spectra and the intensity of emission bands are analyzed and discussed in detail. We further successfully test and verify that intensity ratios RE, of H-2(11/2) -> I-4(15/2) and S-4(3/2) -> I-4(15/2) and R-Tm of (1)G(4) -> H-3(5) and H-3(4) -> H-3(6) are sensitive to temperature, and the population of active ions follows Boltzmann-type population distribution very well. These luminescent nanothermometers could be applied over a wide temperature range from 123 to 423 K with high sensitivity, which enable them to be excellent candidates for temperature sensors.