The novel red-emitting BaBi_2−xEu_xB₄O₁₀ (x = 0.05, 0.1, 0.2, 0.25, 0.3, 0.4, 0.5, 0.6) phosphors were obtained by a crystallization from a glass. Distribution of the Eu³⁺ ions over cation sites were refined for x = 0.1, 0.3 and 0.4 from single-crystal X-ray diffraction data. Emission and excitation spectra of the Eu³⁺-doped BaBi₂B₄O₁₀ phosphors were investigated for the first time, where it was shown that characteristic lines are attributed to the intraconfigurational 4f-4f transitions. The optimal concentration for the BaBi_2−xEu_xB₄O₁₀ phosphors is x = 0.4, after which a luminescence intensity decreases. The CIE chromaticity coordinates for the BaBi₂B₄O₁₀:Eu³⁺ (x = 0.4) phosphor (0.65, 0.35) are close to the NTSC standard values (0.67, 0.33) for commercial red phosphor. The obtained results show that the BaBi₂B₄O₁₀:Eu³⁺ phosphors are promising candidates for solid state lighting application.

A novel non-centrosymmetric NdSr₄O(BO₃)₃ borate and solid solutions of Nd(Ca_1−xSr_x)₄O(BO₃)₃ (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.7, 1.0) were synthesized by solid-state reactions as well as crystallization from a melt. The crystal structures of the Nd(Ca_1−xSr_x)₄O(BO₃)₃ solid solutions with x = 0.2, 0.5 and 1.0 were determined from single crystal X-ray diffraction data and refined in the monoclinic space group Cm to R_obs = 0.028, 0.034 and 0.028, respectively. The thermal expansion of the samples with x = 0, 0.2 and 0.5 was investigated using powder high-temperature X-ray diffraction in the temperature range of 25–1000 °C. A similarity of the thermal and compositional (Ca-Sr substitution) deformations of Nd(Ca_1−xSr_x)₄O(BO₃)₃ solid solutions is revealed: Heating of Nd(Ca_0.5Sr_0.5)₄O(BO₃)₃ by 1 °C leads to the same deformations of the crystal structure as increasing the amount of Sr atoms in Nd(Ca_0.5Sr_0.5)₄O(BO₃)₃ by 0.26 at% Sr. The SHG signal of the series of Nd(Ca_1−xSr_x)₄O(BO₃)₃ solid solutions has a maximum at approximately x = 0.2.