Tuning the Excitonic and Plasmonic Properties of Copper Chalcogenide Nanocrystals

Abstract

The optical properties of stoichiometric copper chalcogenide nanocrystals (NCs) are characterized by strong interband transitions in the blue part of the spectral range and a weaker absorption onset up to ~1000 nm, with negligible absorption in the near-infrared (NIR). Oxygen exposure leads to a gradual transformation of stoichiometric copper chalcogenide NCs (namely, Cu(2-x)S and Cu(2-x)Se, x = 0) into their nonstoichiometric counterparts (Cu(2-x)S and Cu(2-x)Se, x > 0), entailing the appearance and evolution of an intense localized surface plasmon (LSP) band in the NIR. We also show that well-defined copper telluride NCs (Cu(2-x)Te, x > 0) display a NIR LSP, in analogy to nonstoichiometric copper sulfide and selenide NCs. The LSP band in copper chalcogenide NCs can be tuned by actively controlling their degree of copper deficiency via oxidation and reduction experiments. We show that this controlled LSP tuning affects the excitonic transitions in the NCs, resulting in photoluminescence (PL) quenching upon oxidation and PL recovery upon subsequent reduction. Time-resolved PL spectroscopy reveals a decrease in exciton lifetime correlated to the PL quenching upon LSP evolution. Finally, we report on the dynamics of LSPs in nonstoichiometric copper chalcogenide NCs. Through pump-probe experiments, we determined the time constants for carrier-phonon scattering involved in LSP cooling. Our results demonstrate that copper chalcogenide NCs offer the unique property of holding excitons and highly tunable LSPs on demand, and hence they are envisaged as a unique platform for the evaluation of exciton/LSP interactions.

New materials for tunable plasmonic colloidal nanocrystals

“…By comparing the XRD and optical spectra recorded during the evolution of the NCs from the stoichiometric to the non-stoichiometric compound, they confirmed that the appearance of the LSPR was correlated with the introduction of copper vacancies in the NCs. 22 They also verified that the LSPR energy shifted to higher energies when the size of the NCs was reduced from 6 nm to 3 nm, a behaviour that is known in metal NCs and which is attributed to increased scattering of the free carriers with the NC surface as the size of the NCs decreases (see also the introductory section of this review on the Drude model). 1 They also monitored the fluorescence of Cu 2Àx S NCs as a function of the Cu stoichiometry ( Fig.…”

“…15 Kriegel et al extended these studies to the whole family of copper chalcogenides (Cu 2Àx S, Cu 2Àx Se, Cu 2Àx Te). 22 Differently from Dorfs et al, 15 they used diisobutylaluminium hydride instead of Cu + ions as a reducing agent to quench the plasmon resonance and in their case the crystal structure did change during the reduction process. They attributed the stoichiometry change to a reduction of Cu 2+ species inside the NCs to Cu + , triggered by chemically injected electrons.…”

“…The quenching of the fluorescence, which went hand in hand with the appearance of a LSPR, was attributed to several processes: Auger recombination, presence of trap states and exciton-plasmon energy transfer. 22 Copper telluride NCs too have been investigated in detail. Yang et al 50 and Li et al 51 51 An interesting approach is to combine in one heterostructure a metallic and a doped semiconductor domain.…”

Focused Ultrasound‐Augmented Delivery of Biodegradable Multifunctional Nanoplatforms for Imaging‐Guided Brain Tumor Treatment

“…The obtained HCu nanosystems exhibit strong localized surface plasma resonance in NIR region, which is attributed to numerous vacancies arising from copper deficiency 18. Moreover, the absorption at 808 nm is linearly increased with the elevated Cu concentration (Figure S6, Supporting Information).…”

Doped Nanocrystals as Plasmonic Probes of Redox Chemistry

“…[8,9] Others have shown similar LSPRs in nanocrystals of copper(I) selenide and copper(I) telluride. [10][11][12][13][14][15][16] LSPR tunability by variation of the copper vacancy concentration has also been demonstrated by the Alivisatos and Manna groups: the greater the vacancy concentration, the higher the LSPR frequency. [9,10] Metal nanoparticles do not possess such tunability, as their free carrier concentrations are large and difficult to perturb appreciably.…”