Order-disorder phase transitions significantly improving the upconversion luminescence intensity of BiTa7O19:Er3+/Yb3+

BiTa7O19 (BTO) has two lattice structure, P-6C2 (188) ordered phase and P63/mcm (193) disordered phase. Ordered and disordered BTO:Er3+/Yb3+ upconversion phosphors (UCPs) were obtained by solid sintering with different temperatures. The lattice structure of all the samples was investigated by XRD, SEM and Raman spectroscopy, and upconversion luminescence (UCL) spectra were tested by spectrometers. The green integral UCL intensity of the disordered BTO:Er3+/Yb3+ UCP is 60.76 times than that of the ordered sample. By comparing Er3+/Yb3+ co -doped and Er3+ single -doped UCPs with different structures, it is found that the disordered structure enhances the energy transfer from Yb3+ to Er3+, which may be caused by the disordered structure reducing the distance between Yb3+ and Er3+. The absolute temperature sensitivity of the sample with the highest UCL intensity is 0.01005 K-1 at 352 K. All results suggest that the disordered structure of BTO host can greatly improve green UCL intensity and the disordered BTO:Er3+/Yb3+ UCPs are suitable for the application of optical temperature measurement.