Enhancement of upconversion luminescence in NaBiF4: Er3+/Yb3+/Lu3+ for temperature detection

Optical thermometer has got lots of attention by virtue of non-contact, fast response speed, high sensitivity, anti-interference ability, which is less affected by the environment. However, most fluorescent thermometers still suffer from low sensitivity. Here, an optical thermometer based on NaBiF4: Er3+/Yb3+/Lu3+ with enhanced upconversion luminescence is reported. The sample emits strong green light of Er3+ under 980 nm laser excitation and with the increase of Lu3+, the whole luminescence intensity of NaBiF4: 2 % Er3+/20 % Yb3+/ 2.5 % Lu3+ is enhanced by about 3 times, which due to local crystal field distortion. Meanwhile, the lifetime of Er3+ is prolonged and the temperature detection performance is also improved with the substitution of Lu3+. The relative sensitivity reaches a maximum of 0.841 % K-1 at 301 K. The results suggest that it is an optical nanothermometer with great potential.