Novel Red-Emitting BaBi2B2O7:Sm3+ and BaBi2B2O7:Sm3+,Eu3+ Co-Doped Phosphors: Study of the Crystal Structure, Luminescence and Thermal Expansion

The novel polycrystalline phosphors BaBi2 − xSmxB2O7 (х = 0.05, 0.1, 0.15, 0.2, 0.3, 0.4, 0.5), BaBi2 − x − 0.05EuxSm0.05B2O7 (х = 0.35, 0.4, 0.45) and BaBi2 − 0.15 − yEu0.15SmyB2O7 (y = 0.05, 0.1, 0.15, 0.2, 0.3) were obtained by crystallization from a glass-ceramics. The BaBi1.95Sm0.05B2O7 and BaBi1.7Sm0.3B2O7 crystal structures were refined by single crystal X-ray diffraction data to R = 0.059 and 0.054 respectively. The distribution of the Sm3+ ions over cation sites was investigated, and the Sm3+ atoms occupy the M2 site in the Bi subposition. Thermal expansion of BaBi1.7Sm0.3B2O7 was investigated by high-temperature powder X-ray diffraction. The maximum thermal expansion is along the c axis. Such a character of the thermal expansion can be related to the preferred orientation of the BO3 radicals located in the ab plane. Borates are thermally stable in the studied temperature range. Thermal analysis of the BaBi1.7Sm0.3B2O7 borate was performed using differential scanning calorimetry and thermogravimetry. No mass loss was observed according to thermogravimetry data. In comparison with glass ceramics BaBi2B2O7, it can be concluded that activation of the crystal matrix by Sm3+ ions leads to an increase in the crystallization temperature from the melt from 540 to 660°C and an insignificant increase in the melting temperature from 630 to 635°C. Luminescence spectra, excitation and kinetic curves of the BaBi2−xSmxB2O7, BaBi2 − x − 0.05EuxSm0.05B2O7 and BaBi2 − 0.15 − yEu0.15SmyB2O7 series are reported. The maximum luminescence intensity of BaBi2 − xSmxB2O7 and BaBi2 − 0.15 − yEu0.15SmyB2O7 concentration series is observed for the x = 0.05 and x = 0.10 respectively. The novel BaBi2 − x − 0.05EuxSm0.05B2O7 and BaBi2 − 0.15 − yEu0.15SmyB2O7 solid solutions is a promising tunable red-emitting phosphors.