An effective way to improve near-infrared-II luminescence and optical thermometry performance via Gd3+ incorporation in Er3+, Yb3+: ZrO2 nanocrystals

The optical nano-thermometers with near-infrared-II (NIR-II) luminescence (1000 similar to 1700 nm) have drawn growing interest owing to the unique merits such as deep-tissue penetration and excellent spatial resolution. Herein, we report a simple way to improve the NIR-II luminescence and temperature sensing sensitivity simultaneously in Er3+/Yb3+: ZrO2 nanocrystals with the introduction of Gd3+ ions. X-ray diffraction and transmission electron microscopy measurements validate that the addition of Gd3+ ions can change the host lattice parameter and decrease the crystalline grain size of the samples. The optical investigation shows that the remarkable enhancements in the NIR-II emissions of Yb3+ (1036 nm) and Er3+ (1527 nm) are realized via Gd3+ doping under 980 nm excitation, which can be interpreted based on the accelerated radiative transition rate and non-radiative Yb3+-Er3+ energy transfer rate. Meanwhile, the thermal sensing sensitivity of the samples shows a strong dependence on the Gd3+ concentrations, when the fluorescence intensity ratio between Yb3+: F-2(5/2)-> F-2(7/2) and Er3+: I-4(13/2)-> I-4(15/2) transitions is chosen for temperature sensing. Both the optimal NIR-II luminescence and thermal sensitivity are achieved in 1 mol%Gd3+ co-doped sample. The proposed route here may help in the development of efficient NIR-II luminescence materials for thermometry in the biological and medical fields.

Automated summary

The introduction of Gd3+ ions can enhance the NIR-II emissions of Yb3+ and Er3+ in Er3+/Yb3+:ZrO2 nanocrystals, leading to improved thermal sensing sensitivity. The optimal NIR-II luminescence and thermal sensitivity are achieved in samples co-doped with 1 mol% Gd3+.