Effect of annealing temperature and doping concentration on optical properties of Cr3+ doped LiAlP2O7 phosphors

Abstract

In this study, near-infrared (NIR) emitting LiAlP2O7Cr3+ phosphors were synthesized via a conventional solid-state reaction method. To optimize the material’s properties, Cr3+ doping concentrations were varied from 2% to 14%, with annealing temperatures investigated in the range of 600°C to 800°C. X-ray diffraction (XRD) analysis demonstrated that the phase evolution of the material is highly temperature dependent, with the target phase formed at 700-750°C. Upon further increasing the sintering temperature to 800 °C and 900 °C, additional secondary phases with relatively high intensity appeared due to evaporation of Li2O. The obtained phosphor powders exhibit particle sizes on the order of micrometers and show three main absorption regions: a UV band at 293 nm, a blue band at 444 nm, and another red band at 652 nm. The LiAlP2O7:Cr3+ phosphor exhibits broad near-infrared emission spanning from 700 to 1000 nm. The optimal sample, LiAlP2O7:10%Cr3+ was obtained at 750°C for 15 h in air, showing maximum emission at 800 nm under 443 nm excitation. This research shed light on the potential of LiAlP2O7:xCr3+ for Cr3+-based NIR phosphor applications.