Up-Converting Luminescence and Temperature Sensing of Er(3+)/Tm(3+)/Yb(3+) Co-Doped NaYF(4) Phosphors Operating in Visible and the First Biological Window Range

Accurate and reliable non-contact temperature sensors are imperative for industrial production and scientific research. Here, Er(3+)/Tm(3+)/Yb(3+) co-doped NaYF(4) phosphors were studied as an optical thermometry material. The typical hydrothermal method was used to synthesize hexagonal Er(3+)/Tm(3+)/Yb(3+) co-doped NaYF(4) phosphors and the morphology was approximately rod-like. The up-conversion emissions of the samples were located at 475, 520, 550, 650, 692 and 800 nm. Thermo-responsive emissions from the samples were monitored to evaluate the relative sensing sensitivity. The thermal coupled energy level- and non-thermal coupled energy level-based luminescence intensity ratio thermometry of the sample demonstrated that these two methods can be used to test temperature. Two green emissions (520 and 550 nm), radiated from (2)H(11/2)/(4)S(3/2) levels, were monitored, and the maximum relative sensing sensitivities reached to 0.013 K(−1) at 297 K. The emissions located in the first biological window (650, 692 and 800 nm) were monitored and the maximum relative sensing sensitivities reached to 0.027 (R(692/650)) and 0.028 K(−1) (R(692/800)) at 297 K, respectively. These results indicate that Er(3+)/Tm(3+)/Yb(3+) co-doped NaYF(4) phosphors have potential applications for temperature determination in the visible and the first biological window ranges.