Influence of Glass Composition on the Luminescence Mechanisms of CdSe Quantum-Dot-Doped Glasses

In
this work, we characterized the electronic structure of CdSe
quantum dots embedded in a series of x Na2O, (1–x) SiO2 glass matrices (x = 0, 0.25, 0.33, and 0.5). We analyzed the impact of the
glass matrix composition on both the atomic structure of the quantum
dot (QD) and the QD/glass interface, as well as the luminescence mechanisms,
using density functional theory calculations. The increase of Na2O content in the glass matrices was found to promote the formation
of Cd–O and Se–Na interfacial bonds and disrupt the
Cd–Se bonds network. In particular, we show that the glass
composition directly affects the nature of the highest occupied molecular
orbitals (HOMO). According to the atomic structure, band gap distribution,
and density of states calculation, we find that there is significant
reconstruction of the QD and that the picture sometimes proposed of
a “pristine quantum dot” surrounded by glass is not
realistic. The introduction of CdSe QD significantly decreased the
HOMO–LUMO gap of the glass compared to pristine glasses, and
the interfacial bonds greatly contributed to the frontier orbitals
without forming midgap states. We propose a new energy diagram, quite
different from the traditional model, to explain the luminescence
of CdSe quantum-dot-doped glasses, originating from the intrinsic
emission of this hybrid system {QD + glass}. These results improve
our understanding of the luminescence of CdSe quantum-dot-doped glasses,
explaining the reason for the poor quantum efficiency and broad emission
linewidth compared with their colloidal counterparts.