The impact of surface structure and band gap on the optoelectronic properties of Cu2O nanoclusters of varying size and symmetry†
A systematic characterization of Cu2O nanoclusters using classical electrodynamics and time-dependent density functional theory (TDDFT) is performed to investigate their response to light with the alteration of size and symmetry. Absorption and scattering play a crucial role in tuning the surface plasmon resonance (SPR), which is the focal feature of optoelectronic properties. In larger dimensions the SPR is found to be strongly influenced by scattering and in smaller NPs it is dominated by absorption. A blue shift of the SPR peak is observed with decreasing cluster size. The optical properties of Cu2O nanoclusters are also affected by the symmetry aspect. With the variation of size and symmetry the associated surface structure and band gap are also varied. The TDDFT calculation is performed to explore the impact of these two fundamental factors on the optoelectronic nature of (Cu2O)n clusters. The TDDFT study on Cu2O nanoclusters reveals the nature of electronic excitations in photoirradiated (Cu2O)n clusters for n = 1, 2, and 3. The transitions involved in (Cu2O)n are basically categorized as ligand to metal charge transfer (LMCT) and metal to metal charge transfer (MMCT) processes. The change in absorption with varying cluster dimension and symmetry is found to be critically controlled by the relative probabilities of LMCT and MMCT processes. A competing surface reconstruction effect and occupied–virtual energy gap are also found to govern the SPR pattern of the Cu2O nanoclusters. All of these observations provide an appropriate guideline to tune SPR of Cu2O NPs for specific applications.