In this study, a novel narrow-band long-wave ultraviolet (UVA) phosphor, Ba[B₈O₁₁(OH)₄]: Eu²⁺ (BBH:Eu²⁺), was synthesized via a low-temperature self-reduction method. The structural and luminescent properties of the phosphor were systematically characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), diffuse reflectance spectroscopy (DR), density functional theory (DFT) calculations, photoluminescence spectra (PL), thermoluminescence spectra (TL), and decay time curves (DT). The SEM results revealed that the phosphor exhibits a well-defined hexagonal plate-like morphology with dimensions of approximately 1.39±0.31 μm in length and 0.68±0.17 μm in width. The DR experimental results demonstrate that BBH exhibits high reflectivity in the ultraviolet region. DFT calculations indicate that this material is a direct-bandgap semiconductor with a bandgap energy of 5.55 eV. TGA results indicate that the thermal decomposition of BBH occurs at 420 ℃. The excitation spectrum of BBH:Eu²⁺ features a broad peak between 200 to 360 nm, peaking at 277 nm, while the emission spectrum spans from 300 to 420 nm, peaking at 385 nm with a full width at half maximum (FWHM) of 35 nm, exhibiting typical narrow-band UVA emission features. The quantum yield of BBH:2%Eu²⁺ was determined to be 34.6%, and the corresponding decay time was measured as 727 ns. When the temperature increased to 100 ℃, the luminescence intensity of BBH:2%Eu²⁺ decreased to 48.9% of its initial value at room temperature, indicating relatively poor thermal stability. The underlying cause can be attributed to the material's large Stokes shift, which reaches 10127 cm^-1 (108 nm). This large Stokes shift significantly enhances the electron-phonon coupling effect, thereby negatively impacting thermal stability. The observed thermal quenching behavior is primarily governed by the thermally activated cross-relaxation mechanism. Based on the XPS and TL data, the self-reduction mechanism of Eu³⁺ within the BBH matrix was elucidated. This research not only introduces a new approach for synthesizing Eu²⁺-activated phosphors but also successfully develops a high-performance UVA narrow-band phosphor with significant potential for applications in anti-counterfeiting, medical diagnostics, and other fields.

Key words: UVA phosphor, low-temperature self-reduction method, Ba[B₈O₁₁(OH)₄]:Eu²⁺, thermal quenching mechanism