Significant enhancement in Eu3+/Eu2+ emissions intensity by CdS quantum dots, in chloroborosilicate glasses

Abstract

Eu3+ and CdS were singly doped and co-doped into chloroborosilicate glasses with composition 37.8SiO2–27B2O3–18BaO–3.6K2O–3.6Al2O3–10BaCl2 (mol%), by one-step melt quench technique. The samples were characterized by transmission electron microscopy (TEM), UV–Vis absorption, excitation, and emission spectroscopy. TEM images revealed the presence of CdS quantum dots (QDs) of size 5–20 nm in the CdS-doped glasses. The Eu-doped glass shows characteristic orange emission of Eu3+ at 393 nm excitation, while excitation at 250 and 317 nm revealed the existence of Eu2+ ions. There are strong evidences of energy transfer involving the charge transfer band (CTB) and different energy levels of Eu2+ and Eu3+ ions. The CdS-doped glass showed broad emission bands, originating from various electronic transitions involving defect and trap states in CdS crystalline structure. The emission band in the lower wavelength region, shows a red shift with increasing excitation wavelength, which proves the quantum confinement effect in CdS QDs. Eu/CdS co-doped glasses showed significant enhancements in Eu3+/Eu2+ emissions, up to 20 and 70 times, upon excitations at 393 and 317 nm, respectively, which is considerably higher compared to previously reported similar systems. This enhancement is attributed to a complex energy transfer occurring between Eu2+/Eu3+ and CdS QDs, reported for the first time in a glassy system, especially considering the in-situ growth of the QDs during melt. The co-doped glass also showed pure white emission at 6–7 nm slit width upon 387 nm excitation, which is a novel finding from an Eu/CdS co-doped glass.