Blue luminescence of Au nanoclusters embedded in silica matrix

TL;DR

This study investigates the blue luminescence of gold nanoclusters embedded in silica, combining experimental photoluminescence measurements with first-principles calculations to understand size-dependent spectral shifts.

Contribution

It provides new insights into the size-dependent blue shift of luminescence peaks in Au nanoclusters through combined experimental and theoretical approaches.

Findings

Blue luminescence peaks at 3.1 eV and 3.4 eV linked to specific band structure features.

Observed blueshift of 0.1 eV with decreasing cluster size explained by strain effects.

First-principles calculations support the experimental size-dependent spectral shifts.

Abstract

Photoluminescence study using the 325 nm He-Cd excitation is reported for the Au nanoclusters embedded in SiO2 matrix. Au clusters are grown by ion beam mixing with 100 KeV Ar+ irradiation on Au [40 nm]/SiO2 at various fluences and subsequent annealing at high temperature. The blue bands above ~3 eV match closely with reported values for colloidal Au nanoclusters and supported Au nanoislands. Radiative recombination of sp electrons above Fermi level to occupied d-band holes are assigned for observed luminescence peaks. Peaks at 3.1 eV and 3.4 eV are correlated to energy gaps at the X- and L-symmetry points, respectively, with possible involvement of relaxation mechanism. The blue shift of peak positions at 3.4 eV with decreasing cluster size is reported to be due to the compressive strain in small clusters. A first principle calculation based on density functional theory using the full potential linear augmented plane wave plus local orbitals (FP-LAPW+LO) formalism with generalized gradient approximation (GGA) for the exchange correlation energy is used to estimate the band gaps at the X- and L-symmetry points by calculating the band structures and joint density of states (JDOS) for different strain values in order to explain the blueshift of ~0.1 eV with decreasing cluster size around L-symmetry point.