Ratiometric temperature sensing behavior of dual-emitting Ce3+/Tb3+ co-doped Na5Y9F32 single crystal with high relative sensitivity

Abstract

The Na5Y9F32 single crystals doped with fixed 0.5 mol% Ce3+ and various concentrations of Tb3+ (0, 0.4, 0.6 and 0.8 mol%) were grown by Bridgeman method. The luminescent properties, energy transfer (ET) and the ratiometric temperature sensing behavior were studied thoroughly. Under 315 nm excitation, the Ce3+/Tb3+ co-doped Na5Y9F32 single crystal mainly presented two emissions at blue 385 nm (Ce3+:5d→4 f) and green 545 nm (Tb3+:5D4→7F5). The color area can undergo from the purple-blue region (0.1643, 0.0768) to the green region (0.2585, 0.3604) by altering the content of Tb3+ ion from 0 to 0.8 mol%. The energy transfer between the Ce3+ and Tb3+ ions was confirmed by decay curves with emission spectra, and the maximum energy transfer efficiency (ETE) were estimated to be 45.1%. The mechanism of dipole-dipole interaction (d-d) for energy transfer from Ce3+ to Tb3+ can be explained by the formula of Dexter’s energy transfer. The fluorescence intensity ratio (FIR) of blue and green emission showed a linear relationship with temperature varying from 298 K to 473 K in the 0.5 mol% Ce3+/0.8 mol% Tb3+ co-doped Na5Y9F32 single crystal. Meanwhile, the 0.5 mol% Ce3+/0.8 mol% Tb3+ co-doped Na5Y9F32 single crystal possessed higher absolute sensitivity (Sa) of 0.0157 K−1, relative sensitivity (Sr) of 1.18% K−1 and temperature resolution (δT) of 0.086 K. By using the integrating spheres, the quantum yield (QY) of 0.5 mol% Ce3+/0.8 mol% Tb3+ co-doped Na5Y9F32 single crystal was measured as ~16.88%. These excellent optical properties suggest that the Ce3+/Tb3+ co-doped Na5Y9F32 single crystal with stable physical-chemical properties could have a far-reaching application prospect for the ratiometric optical thermometry.