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

Abstract

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(0.5Eu2O3)1 and (B2O3)z(PbO)99.6-z(0.5Eu2O3)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 Eu3+ 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 B2O3 content are given. The quantitative analysis of 5D0 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 cm2, 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.