Glass composition and excitation wavelength dependence of the luminescence of Eu³⁺ doped lead borate glass

This work explores the relationship between the bandwidth of luminescence spectral features and their relative intensities, using glasses doped with europium, Eu³, over a wide composition range. Glasses of composition (B₂O₃)₇₀(PbO)₂₉(0.5Eu ₂O₃)₁ and (B₂O₃) _z(PbO)_99.6-z(0.5Eu₂O ₃)_0.4, (z 20, 30, 40, 60, 70), were prepared by the melting-quenching technique. Variable-wavelength measurements by the prism-coupling method enabled interpolation of refractive index at selected wavelengths. Diffuse reflectance spectra confirmed the incorporation of Eu ³ into the glass, and scanning electron microscopy displayed that this was in a homogeneous manner. Vibrational spectra showed a change in boron coordination from BO₃ to BO₄ units with increase of PbO content in the glass. Multi-wavelength excited luminescence spectra were recorded for the glasses at temperatures down to 10 K and qualitative interpretations of spectral differences with change of B₂O ₃ content are given. The quantitative analysis of ⁵D ₀ luminescence intensity-bandwidth relations showed that although samples with higher boron content closely exhibit a simple proportional relationship with band intensity ratios, as expected from theory, the expression needs to be slightly modified for those with low boron content. The Judd-Ofelt intensity analysis of the ⁵D₀ emission spectra under laser excitations at low temperature gives Ω₂ values within the range from (3.9-6.5) × 10^-20 cm², and Ω₄ in the range from (4.1-7.0) × 10^-20 cm ², for different values of z. However, no clear monotonic relation was found between the parameter values and composition. The Judd-Ofelt parameters are compared with those from other systems doped with Eu³ and are found to lie in the normal ranges for Eu³-doped glasses. The comparison of parameter values derived from the 10 K spectra with those from room temperature spectra for our glasses, which are fairly constant for different compositions, shows that site selection occurs at low temperature.