Tailoring up-conversion luminescence for single band located in first biological windows and optical thermometry of Yb3+/Ln3+ (Ln = Er, Tm) doped oxyfluoride ceramics via Cr3+ doping

Abstract

Successful up-conversion luminescence (UCL) tuning from multi-bands to a single band located in first biological windows (BW-1) was realized in oxyfluoride ceramics doped with Yb3+/Ln3+ (Ln = Er, Tm) via Cr3+ doping. Based on UCL spectra, decay curves and diffuse reflectance spectra (DRS) of β-PbF2:Yb3+/Er3+/Cr3+ oxyfluoride ceramics with different Cr3+ contents, strong energy transfer between Cr3+ and Er3+ ions was confirmed to explain the UCL tuning mechanism. In β-PbF2:Yb3+/Tm3+/Cr3+ system, besides energy transfer between Cr3+ and Tm3+ ions, that Cr3+ ions doping into β-PbF2 nanocrystals absorbing the blue and other higher-energy emissions of Tm3+ ions directly was the leading role of β-PbF2:Yb3+/Tm3+/Cr3+ exhibiting an intense single red emission under 980 nm laser excitation. Additionally, the potentiality of β-PbF2:Yb3+/Ln3+/Cr3+ (Ln = Er, Tm) oxyfluoride ceramics as optical thermometry operating in the first biological window (BW-I) was evaluated on the basis of a thermo-responsive fluorescence intensity ratio (FIR) of the Stark sublevels of 4F9/2 → 4I15/2 transitions of Er3+ ion and deep-red (700 nm) to NIR emission (800 nm) from completely separated 3F3/3H4→3H6 transitions of Tm3+ ion. These results offer a promising strategy to manipulate single band UCL located in BW-1 region for the deep tissue imaging. And temperature dependent UCL properties of Ln3+ (Ln = Er, Tm) doped fluoride nanocrystals has great potential applications as biological thermometry.