Improved up-conversion behaviors and temperature sensitivity based on Stark sublevels of Er3+ in β-NaYF4:Yb3+, Er3+ and β-NaYF4: Yb3+, Er3+@NaGdF4

Rare earth ions doped core-shell thermometers exhibit improved up-conversion emission behaviors, while the thermal sensitivity is not higher than the corresponding core-only structured luminescent thermometers via the thermal coupled levels based luminescence intensity ratio (LIR) technique. In this work, the core-only beta-NaYF4: 16Yb(3+), 4Er(3+) (C-4Er) up-conversion nanoparticles (UCNPs) and the sub 25 nm core-shell beta-NaYF4: 16Yb(3+), 4Er(3+)@0.5NaGdF4 (CS-4Er@0.5Gd) and beta-NaYF4: 16Yb(3+), 4Er(3+)@1NaGdF(4) (CS-4Er@1Gd) UCNPs have been successfully synthesized by seed-mediated growth methods for temperature detection. The spectral study indicated that the up-conversion luminescence intensity of CS-4Er@0.5Gd and CS-4Er@1Gd was obviously enhanced compared withC-4Er. Luminescence intensity ratio originated from thermally coupled Stark sublevels (Stark-LIR) of Er3+ (2H11/2(1)(2), 4S3/2(1)(2)(3)) of CS-4Er@0.5Gd and CS-4Er@1Gd has been firstly applied to calculated the relative thermal sensitivity (S-R) of core-shell UCNPs. As a result, S-R of CS-4Er@1Gd is the largest among the considered UCNPs, and is increased from 10.95 x 10(-3)/K (LIR) to 17.80 x 10(-3)/K (Stark-LIR), indicating that with Stark-LIR techniques, the nano core-shell sensors behave a larger SR than core-only structured thermometers. This work may lead to an appropriate approach to improve the temperature sensitivity of core-shell thermometers for temperature sensing.

Automated summary

This study successfully synthesized core-shell up-conversion nanoparticles and found that they exhibit improved thermal sensitivity compared to core-only structured thermometers. The spectral study showed that the up-conversion luminescence intensity of the core-shell nanoparticles was significantly enhanced. The use of Stark-LIR techniques allowed for the calculation of the relative thermal sensitivity of the core-shell nanoparticles, with CS-4Er@1Gd showing the highest sensitivity.