Amphoteric properties of gold in zinc selenide

Quantized Electronic Doping towards Atomically Controlled “Charge-Engineered” Semiconductor Nanocrystals

“…Structural and analytical characterization, combined with spectroscopic measurements and chemical etching experiments, indicate that the clusters consist of seven gold atoms and that they seed the nucleation of CdSe NC containing an equivalent number of gold impurities preferentially located in the particle core. Consistent with previous studies of bulk materials [39][40][41][42][43] , the dopants are found to incorporate as Au + acceptors. In NCs, owing to the quantum confinement effect, this results in long-lived, widely Stokes-shifted luminescence, spectrally tuneable from the visible to the near infrared by control of the particle size.…”

“…The spectral and dynamical behaviours of the Au:CdSe NCs are in full agreement with the Au-mediated recombination process observed in gold-doped II-VI bulk chalcogenides, where the full d-shell of the Au impurity gives rise to a deep acceptor level in the host forbidden gap [39][40][41][42][43][44][65][66][67] , which participates in the recombination process of BE excitons following the scheme depicted in the inset of Figure 2a. Specifically, following NC excitation (Step 1), the photohole in the NC valence band (VB) is rapidly captured by Au + which temporarily changes its oxidation state to Au 2+ (Step 2), thereby becoming optically-active for the subsequent radiative recombination of a conduction band (CB) electron (Step 3) 39,[41][42][43][44][66][67][68][69] . Spectro-electrochemical measurements in Concomitantly, excess electrons accumulating in surface defects become efficient traps for VB photoholes.…”

“…Transient transmission measurements as a function of the excitation fluence, discussed later in this work, corroborate this picture, showing an Auger-dominated biexciton lifetime of ~10 ps, consistently with Auger relaxation of negative trions occurring on a timescale faster than the time resolution of our spectro-electrochemistry setup (~1.5 ns), even considering a strong asymmetry between the contributions by the negative and the positive trion pathways to the biexciton Auger decay 73,74 . Importantly, since the Au + acceptor state is pinned to the host valence band 34,[36][37][38][39][56][57][58][59] , the dopant-mediated emission is tuneable by control of the particle size, whereas the Stokes shift is essentially independent of quantum confinement. The spectral tunability from the visible to the near IR regions achievable by doping CdSe NCs with gold is emphasized in Figure 2d and Supporting Figure S7, where we report the energy position of the 1S absorption peak and of the Au-PL for two sets of Au:CdSe NCs ranging different particle size regimes (~0.9-1.05 nm and ~1.35-1.65 nm) controlled by the amount of OA ligands used in the synthesis 75 .…”

“…For example, direct colloidal synthesis or cation exchange routes are established only for II–VI or III–V NCs doped with copper, silver, iron, or indium, ,,,− whereas NCs doped with aluminum have been only once reported by Norris and co-workers . On the other hand, doping with an important amphoteric electronic impurity such as gold, which is a known p -type dopant capable of assuming +1, + 3, as well as +2 oxidation states in bulk II–VI semiconductors, − has never been reported in NCs. Au-doping has been successfully obtained in InP NCs where In 3+ cations have been substituted with Au 3+ cations. , …”

Low temperature II–VI nanowire growth using Au–Sn catalysts

“…Even though Au 0.7 Sn 0.3 forms a deep eutectic on the Au-Sn phase diagram, it was found that higher concentrations of Sn, specifically Au 0.35 Sn 0.65 , yielded nanowires with the best optical quality. This may be because higher concentrations of Au in the catalysts lead to more Au impurities in the nanowires, where they can form interstitial defects that affect the luminescent properties of ZnSe [31]. More specifically, at our growth temperature of 320 1C, solid Zn can dissolve Au concentrations of up to 4 at% [16].…”