Eu2+/Eu3+ activated phosphate glasses synthesized via melting with multi-wall carbon nanotubes

Abstract Glasses of BaO:P2O5 composition were melted with fixed Eu2O3 content and varying amounts of multi-wall carbon nanotubes (MWCNTs) for a spectroscopic and calorimetric study focusing on luminescent properties of interest to light-emitting devices. The optical transmission data indicated favorable Eu3+ → Eu2+ reduction with MWCNTs up to 1.0 wt% as judged by the 4f7 → 4f65d transitions of Eu2+ ions around 320 nm. A small amount of MWCNTs at 0.3 wt% lead to an improved Eu3+ luminescence under 320 nm relative to the Eu3+-doped reference likely due to a Eu2+ → Eu3+ energy transfer. On the other hand, the most intense emission around 450 nm corresponding to 4f65d → 4f7 radiative relaxation in Eu2+ was obtained for a glass melted with 0.7 wt% MWCNTs. Concentration quenching and optical band gap reduction are suggested to cause the decreased 450 nm band emission in the glass melted with 1.0 wt% MWCNTs. The glasses presented concomitant luminescence due to remaining Eu3+ ions, and the resulting emitted light under excitation at 320 nm was characterized by CIE diagram. Further, Raman spectroscopy was employed for a structural characterization, which was ultimately correlated with the thermal properties measured by differential scanning calorimetry.