Phonon-assisted Upconversion Luminescence Thermal Enhancement of NaYS2:Yb3+,Nd3+ for Optical Temperature Sensing

Upconversion luminescence presents obvious advantages in optical temperature sensing, nevertheless the application in complex scenarios is limited by luminescence thermal quenching. Herein, NaYS2:Yb3+,Nd3+ phosphors are synthesized by the solid-gas reaction method and used for temperature sensing. A series of emissions for Nd3+ from visible to near-infrared region are achieved based on energy transfer from Yb3+ to Nd3+ under 980 nm excitation. With elevating the temperature, significant thermal enhancement effect of nearly three orders of magnitude is detected in near-infrared emission of 4F7/2 -> 4I9/2, which is attributed to phonon-assisted energy transfer of Yb3+-> Nd3+ and the corresponding thermal population effect. The thermal behaviors of thermally coupled energy levels for 4G7/2/2G9/2 and 4F7/2/4F5/2 in NaYS2:Yb3+,Nd3+ are evaluated by luminescence intensity ratio technique. Remarkably, the optical thermometer based on the enhanced emission of 4F7/ 2/4F5/2 shows excellent temperature measurement performance, which is expected to be applied in widetemperature-range and highly-sensitive temperature sensing. These results not only provide a pathway to realize high performance temperature sensing, but also heighten the understanding of UC emission thermal enhancement.