Reversible Tunability of the Near-Infrared Valence Band Plasmon Resonance in Cu_2–xSe Nanocrystals

Abstract

We demonstrate that colloidal Cu(2-x)Se nanocrystals exhibit a well-defined infrared absorption band due to the excitation of positive charge carrier oscillations (i.e., a valence band plasmon mode), which can be tuned reversibly in width and position by varying the copper stoichiometry. The value of x could be incrementally varied from 0 (no plasmon absorption, then a broad peak at 1700 nm) to 0.4 (narrow plasmon band at 1100 nm) by oxidizing Cu(2)Se nanocrystals (upon exposure either to oxygen or to a Ce(IV) complex), and it could be incrementally restored back to zero by the addition of a Cu(I) complex. The experimentally observed plasmonic behavior is in good agreement with calculations based on the electrostatic approximation.

Colloidal Cu2−x(SySe1−y) alloy nanocrystals with controllable crystal phase: synthesis, plasmonic properties, cation exchange and electrochemical lithiation

“…in Cu 2Àx Se the value of x is significantly altered. 19 Fig bi-dimensional Fourier transform (2D-FT) patterns (inset of Fig. 2a).…”

New materials for tunable plasmonic colloidal nanocrystals

“…For these NCs, ''self-doping'' can be also achieved via post-synthetic redox processes. 15 (iii) NCs of metal oxides that, due to their intrinsic electronic structure, have conductive behaviour.…”

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.…”

“…In general, conditions which stabilize copper (such as lower m Cu ) favor the forward reaction involving the formation of copper vacancies and valence band holes. For example, copper is much more stable in the form of copper oxide than as Cu 0 ; therefore, the creation of copper vacancies is strongly favored (Scheme 1 a) in the presence of air or other oxidants: [9] Cu 32 S 16 þ 1 Along with CuO, [12] Cu 2 O, known to be stable on the nanoscale, [19] may also be formed. Reducing conditions, on the other hand, favor the backward reaction involving the filling of copper vacancies (Scheme 1 b).…”