Highly uniform and monodisperse β-NaYF₄ : Sm³⁺ nanoparticles for a nanoscale optical thermometer

Monodisperse β-NaYF₄:1%Sm³⁺ nanoparticles were fabricated successfully via the thermal decomposition technique. Strong temperature dependence of the Sm³⁺ emission was observed when its thermally populated state H_7/26 was directly excited to the G_5/24 level. This strategy not only can eliminate laser heating and background Stokes-type scattering noise but also has a high quantum yield as a result of one-photon excitation process. Under 594.0 nm laser excitation, the emission intensity of G_5/24-H_5/26 enhances monotonously with rising temperature from 300 K to 430 K, including a physiological temperature range (27°C-60°C). The relative temperature sensitivity can reach 1.1%   K^-1 and 0.91%  K^-1 at 300 K and 330 K, respectively. In addition, the repeatability of temperature sensing was evaluated under several heating-cooling cycles, and the decay curves of the emission at 560.0 nm (G_5/24-H_5/26) at different temperatures were also investigated. These results raise the prospects of monodisperse β-NaYF₄:1%Sm³⁺ nanoparticles for optical temperature sensing in biomedicine fields.