| Summary: | The present study is aimed at unveiling the luminescence potential of Ba<sub>4−<i>x</i></sub>Sr<sub>3+<i>x</i></sub>(BO<sub>3</sub>)<sub>4−<i>y</i></sub>F<sub>2+3<i>y</i></sub> (BSBF) crystals doped with Eu<sup>3+</sup>, Tb<sup>3+</sup>, and Ce<sup>3+</sup>. Owing to the incongruent melting character of the phase, the NaF compound was used as a solvent for BSBF crystal growth. The structure of BSBF: Eu<sup>3+</sup> with Eu<sub>2</sub>O<sub>3</sub> concentration of about 0.7(3) wt% was solved in the non-centrosymmetric point group <i>P</i>6<sub>3</sub><i>mc</i>. The presence of Eu<sub>2</sub>O<sub>3</sub> in BSBF: Eu<sup>3+</sup> leads to a shift of the absorption edge from 225 nm to 320 nm. The photoluminescence properties of the BSBF: Ce<sup>3+</sup>, BSBF: Tb<sup>3+</sup>, BSBF: Eu<sup>3+</sup>, and BSBF: Eu<sup>3+</sup>, Tb<sup>3+</sup>, Ce<sup>3+</sup> crystals have been studied. The unusual feature of europium emission in BSBF is the intensively manifested <sup>5</sup>D<sub>0</sub>→<sup>7</sup>F<sub>0</sub> transition at about 574 nm, which is the strongest for BSBF: Eu<sup>3+</sup> at 370 nm excitation and for BSBF: Eu<sup>3+</sup>, Tb<sup>3+</sup>, Ce<sup>3+</sup> at 300 nm and 370 nm excitations. No evidence of Tb<sup>3+</sup>→Eu<sup>3+</sup> energy transfer was found for BSBF: Eu<sup>3+</sup>, Tb<sup>3+</sup>, Ce<sup>3+</sup>. The PL spectra of BSBF: Eu<sup>3+</sup> at 77 and 300 K are similar with CIE chromaticity coordinates of (0.617; 0.378) at 300 nm excitation and (0.634; 0.359) at 395 nm excitation and low correlated color temperature which implies application prospects in the field of lightning. Due to the high intensity of <sup>5</sup>D<sub>0</sub>→<sup>7</sup>F<sub>0</sub> Eu<sup>3+</sup> transition at 370 nm excitation, the BSBF: Eu<sup>3+</sup> emission is yellow-shifted.
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