Structure and upconversion analyses of Er3+-doped Ba6Ti2Nb8O30-Sr6Ti2Nb8O30 solid solutions

Er3+-doped filled tungsten bronze Ba6Ti2Nb8O30-Sr6Ti2Nb8O30 solid solutions with different Ba6Ti2Nb8O30/Sr6Ti2Nb8O30 ratios (SBTNx) have been prepared by a high temperature solid-state reaction. The crystal structure has been investigated simultaneously by the Rietveld structural refinement and upconversion photoluminescence (UC-PL) spectra. It is found that the crystal structure of SBTNx changes from TE-FTB symmetry (0≤x≤3, space group P4bm) to OR-FTB symmetry (3.5≤x≤5.91, space group Pba2) with x increasing. More interestingly, the structure transition of SBTNx system is also revealed by the UC-PL spectra which indicate the intimate correlation between the UC-PL spectra and the structure transition. Furthermore, the underlying origin concerning the variation of UC-PL spectra has been studied from crystal structure aspect which suggests UC-PL spectra can be explored as a structure probe for present filled tungsten bronze solid solutions.