Cs2Bi2Sr(P2O7)(PO4)2:Er3+/Yb3+ phosphors for outstanding thermal enhancement of up-conversion under 980 and 1550 nm laser excitations in the 303 to 723 K range

Abstract

A serious of Er3+/Yb3+ co-doped Cs2Bi2Sr(P2O7)(PO4)2 (CBSPO) phosphors are prepared by solid phase reaction method, and the related thermal enhancement of up-conversion luminescence (UCL) are studied in depth under 980 and 1550 nm laser excitations. When doping concentration of Er3+is fixed at 0.1, and doping concentration of Yb3+ is adjusted to improve the thermal enhancement effect in the temperature range from 303 to 723 K. The optimal doping concentrations of Er3+/Yb3+ are found as 0.1 and 0.5, and the maximum enhancement of green UCL emission reaches 5.25 and 16.74 times under 980 and 1550 nm laser excitations, respectively. This is because of the combined action of electronic thermal agitation, phonon assisted transition and lattice distortion of doping Er3+ sites. The change of structure with temperature is studied by variable temperature XRD. Additionally, based on FIR technique, the absolute sensitivity of 0.00955 K−1 at 557 K, 0.00643 K−1 at 509 K are got in CBSPO:0.1Er3+/0.3Yb3+ under 980 nm laser excitation and in CBSPO:0.1Er3+/0.4Yb3+ under 1550 nm laser excitation, respectively. The structure changes of polyphosphate with temperature provide new ideas for development of thermally enhanced up-conversion phosphors, which can be applied as optical thermometer at high temperature environment.