Luminescence properties of Al4B2O9:M (M= Pb2+ and Bi3+) phosphors for down-shifting applications

Abstract

Al4B2O9, Al4B2O9:Pb2+, and Al4B2O9:Bi3+ powders with varying activator concentrations were synthesized via a solution-combustion method. The crystal structure of the prepared materials was confirmed by X-ray diffraction (XRD), while Fourier transform infrared (FTIR) spectroscopy confirmed the presence of characteristic B-O and Al-O bonding. The morphology of the materials was examined using scanning electron microscopy (SEM) and EDS mapping, revealing a dense structure of micron-sized particles with smooth cleavage planes and uniform elemental distributions. Photoluminescence measurements of Al4B2O9:Pb2+ and Al4B2O9:Bi3+ phosphors showed strong ultraviolet excitation and emission in the near-UV region, accompanied by large Stokes shifts. Concentration quenching occurred at critical concentrations of 3.0 mol% for Pb2+ and 1.0 mol% for Bi3+. Increasing dopant content induced a systematic red shift in the Pb2+ series, whereas the Bi3+ series displayed a much smaller spectral shift. The distinct emission behaviors of Pb2+ and Bi3+ allowed for concentration-dependent tuning of the optical properties. These findings suggest that Al4B2O9:M (M = Pb2+, Bi3+) phosphors are promising candidates for luminescent down-shifting applications.