Abstract
Optical thermometry technology plays a significant role in plenty of fields owing to its unrivaled properties such as sensitive, noncontact, reliable. A ratiometric optical thermometer based on Nd3+/Tm3+/Yb3+/Gd3+ Four-doped NaYF4 nanomaterials is developed. Unusually, the 750 nm emission increases with increasing temperature. The 750 nm upconversion (UC) emission from the 4F7/2 energy level of Nd3+ relies on thermally-assisted energy transfer (ET) from the 2F5/2 energy level of Yb3+. According to the fluorescence intensity ratio (FIR) technique, the temperature sensitivity is calculated by measuring the UC emission spectrum of the sample at different temperatures. It is found that the FIR strategy in which the fluorescence intensity of the two wavelengths changes oppositely with the increase in temperature can effectively improve the temperature sensitivity of the material. Especially for the FIR of 4F7/2 → 4I9/2 (Nd3+)/2P3/2 → 4I11/2 (Nd3+), the maximum absolute sensitivity (SA) reaches 3.56 K-1 and the maximum relative sensitivity (SR) reaches 2.89% K−1 in the temperature range of 333–553 K. More importantly, SA and SR are increased at the same time, and have a larger values in the entire temperature range. Therefore, NaYF4: Nd3+/Tm3+/Yb3+/Gd3+ nanomaterials with these demonstrated advantages are very promising for optical thermometry.
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