Relevance. Luminescent properties of materials doped with rare-earth ions have garnered significant interest due to their applications in various fields, including optoelectronics and photonics. Glassy lithium tetraborate (LTB) represents a promising matrix for hosting such ions, offering tunable luminescence properties.Purpose. The purpose of this study was to investigate the concentration dependence of the luminescence spectrum of glassy LTB doped with europium oxide within the spectral range of 300-750 nm.Methodology. Glassy samples of LTB activated by europium oxide were synthesized via a high-temperature process and characterized using photoluminescence (PL) spectroscopy. The PL spectra were recorded in the specified spectral range under excitation by a titanium-sapphire laser. The experimental setup provided insights into the luminescence behavior of the samples at different Eu3+ ion concentrations.Results. The concentration dependence of the photoluminescence spectra of glassy lithium tetraborate Li2B4O7 activated by europium oxide Eu2O3 was investigated in the spectral range of 300-750 nm. The intense emission observed in the wavelength region of 570-720 nm is attributed to the intra-configurational electronic f�f transitions between the excited multiplet levels 5D and the ground multiplet 7F of the Eu3+ ion.Conclusions. The observed transitions, forbidden by selection rules, indicated J-mixing effects. The study highlights the potential of Eu-activated LTB glass for optoelectronic applications and provides insights into the underlying luminescence mechanisms.