Novel optical thermometer through upconversion emission of Ho3+ sensitized by Nd3+

Various concentrations of Ho3+ and Nd3+ codoped NaYF4 nanorods were successfully synthesized. On the basis of the upconversion spectra under 808 nm excitation, the luminescence mechanisms were discussed in detail. The ratio of red to green intensity evidently increases with increasing the Nd3+ content due to the stronger interactions between Ho3+ and Nd3+, which enhance the red emission and suppress the green one. In addition, we found that the red emission is more sensitive to the ambient temperature as compared to the green one, thus validating the thermal sensing by applying the ratiometric method by using these two emission bands. Relatively high sensing sensitivity of 0.9% was obtained, evidencing the great potential of the presented optical thermometer.