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

Abstract

The novel polycrystalline phosphors BaBi_2 − xSm_xB₂O₇ (х = 0.05, 0.1, 0.15, 0.2, 0.3, 0.4, 0.5), BaBi_{2 − x − 0.05}Eu_xSm_0.05B₂O₇ (х = 0.35, 0.4, 0.45) and BaBi_{2 − 0.15 − y}Eu_0.15Sm_yB₂O₇ (y = 0.05, 0.1, 0.15, 0.2, 0.3) were obtained by crystallization from a glass-ceramics. The BaBi_1.95Sm_0.05B₂O₇ and BaBi_1.7Sm_0.3B₂O₇ 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 BaBi_1.7Sm_0.3B₂O₇ 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 BaBi_1.7Sm_0.3B₂O₇ 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 BaBi_2−xSm_xB₂O₇, BaBi_{2 − x − 0.05}Eu_xSm_0.05B₂O₇ and BaBi_{2 − 0.15 − y}Eu_0.15Sm_yB₂O₇ series are reported. The maximum luminescence intensity of BaBi_2 − xSm_xB₂O₇ and BaBi_{2 − 0.15 − y}Eu_0.15Sm_yB₂O₇ concentration series is observed for the x = 0.05 and x = 0.10 respectively. The novel BaBi_{2 − x − 0.05}Eu_xSm_0.05B₂O₇ and BaBi_{2 − 0.15 − y}Eu_0.15Sm_yB₂O₇ solid solutions is a promising tunable red-emitting phosphors.