Blue-LED-excitable NIR-II Luminescent Lanthanide-Doped SrS Nanoprobes for Ratiometric Thermal Sensing

Lanthanide (Ln3+)-doped near infrared (NIR)-II luminescent nanoprobes have shown great promise in many technological fields, but are currently limited by the low absorption efficiency of Ln3+ due to the forbidden 4f→4f transition. Herein, we report a novel NIR-II luminescent nanoprobe based on efficient energy transfer from Ce3+ to Er3+ and Nd3+ in sub-10 nm SrS nanocrystals (NCs), which are excitable by using a commercial blue light-emitting diode (LED). Through sensitization by the allowed 4f→5d transition of Ce3+, the NCs exhibit strong NIR-II luminescence from Er3+ and Nd3+ with quantum yields of 2.9% and 2.3%, respectively. Furthermore, by utilizing the intense NIR-II luminescence of Er3+ from the thermally coupled Stark sublevels of 4I13/2, we demonstrate the application of SrS:Ce3+/Er3+ NCs as blue-LED-excitable NIR-II luminescent nanoprobes for ratiometric thermal sensing. These findings reveal the unique advantages of SrS:Ln3+ NCs in NIR-II luminescence, which may open up a new avenue for exploring novel and versatile luminescent nanoprobes based on Ln3+-doped sulphide NCs.