Spectroscopic investigation of Ho³⁺ and (Ho³⁺ + Au⁰) inclusion on the structural, optical and luminescence attributes of Li₂O + Bi₂O₃ + B₂O₃ + P₂O₅ glasses

The present work aims to study the significant influence of the incorporation of gold nanoparticles (AuNPs) in the Ho³⁺—doped Li₂O + Bi₂O₃ + B₂O₃ + P₂O₅ glasses prepared via the melt quenching method. The prepared glasses were systematically studied using various techniques such as; x-ray diffraction (XRD), high-resolution transmission electron microscope (HR-TEM), differential scanning calorimetry (DSC), ultraviolet–visible-near infrared (UV–vis-NIR) spectroscopy, photoluminescence, and lifetime decay measurements. Furthermore, theoretical JO calculations were performed to investigate and validate the optical properties with experimental results. The structural studies by XRD and HR-TEM reveal the amorphous characteristics of glasses and the presence of metallic gold nanoparticles. The DSC results reveals the thermal stability of the glasses with addition of AuNPs into the glasses as shown by the rise in T_g values from 453 to 498 °C. Optical absorbance spectra demonstrate the existence of 8 electronic transitions in the UV–Vis-NIR region attributable to Ho³⁺ ions and an intensified SPR peak is observed owing to the incorporation of AuNPs. PL spectra exhibit three distinct, notable emission peaks in the visible wavelength region, whose intensity is greatly affected by incorporating AuNPs due to the reduced NR decay rate. Furthermore, JO analysis was carried out to support the experimental results, which reveals that, the JO parameters are in the order; Ω₂ > Ω₄ > Ω₆, demonstrating the covalency nature between the Ho³⁺–O²⁻ bond and the adjacent Ho³⁺ ions. PL emission spectra were used to estimate the chromaticity coordinates, which is in the region of the cool white light region for AuNPs incorporated Ho³⁺- doped glasses. Amongst all, LBBPH05Au. i.e. (0.5 mol% Ho³⁺  + 0.001 mol% Au⁰) doped Li₂O + Bi₂O₃ + B₂O₃ + P₂O₅ glass sample exhibits high quantum efficiency (77.2%), low NR decay rate and white light emission in the cool region.