Single-Particle Photoluminescence Spectra, Blinking, and Delayed Luminescence of Colloidal CuInS₂ Nanocrystals

Abstract

Single-nanocrystal and ensemble photoluminescence measurements on CuInS2 semiconductor nanocrystals reveal intrinsically broad luminescence bandshapes attributable to strong electron-phonon coupling in the emissive excited state, similar to the single-nanocrystal luminescence spectra of Cu +-doped CdSe nanocrystals. This finding is consistent with the hypothesis of exciton self-trapping in CuInS2 NCs, which forms an emissive state similar to those of Cu +-doped nanocrystals. Blinking is observed that resembles that of other semiconductor nanocrystals. Ensemble luminescence measurements reveal the existence of a remarkably long-lived excited state in these nanocrystals that continues to emit photons over several orders of magnitude in time following the excitation pulse. This delayed luminescence is attributed to reversible electron trapping. The delayed luminescence overlaps in time and shows similar distributed kinetics to the blinking "off" times, supporting the proposal that these two phenomena arise from the same microscopic carrier-trapping and-detrapping processes. Excitation power dependence measurements illustrate that the delayed luminescence saturates at very low intensities at the power densities used in single-nanocrystal measurements, consistent with this metastable charge-trapped state being the "off" state of the luminescence blinking cycle.

Photoluminescence Enhancement of CuInS2 Quantum Dots in Solution Coupled to Plasmonic Gold Nanocup Array

“…Figure A shows an angular dark field scanning transmission electron microscope (ADF‐STEM) image of the CIS QDs with an average diameter of ≈4 nm. As typical for this system, the absorption spectrum extending up to ≈800 nm is relatively featureless (Figure B), while the PL peaks at 720 nm with a full width at half‐maximum of 0.36 eV (150 nm), also consistent with previous reports . The broad emission around 720 nm (1.72 eV) of these CIS QDs overlaps the EOT peak of the gold nanocup arrays (Figure C), hence offering a prerequisite for effective plasmon–exciton coupling and PL enhancement of CIS QDs in the hybrid system.…”

Blue Light Emitting Defective Nanocrystals Composed of Earth‐Abundant Elements

“…More specifically, Cu‐In‐S NCs have been suggested to exhibit PL via either a Cu + /Cu 2+ redox couple state or a Cu‐related defect state . A variety of single particle, ultrafast, magneto‐optical, spectroelectrochemical, and temperature‐dependent spectroscopies have been applied to understand the source of broad, efficient PL from Cu‐In‐S NCs with varying degrees of success. However, there has been little manipulation of the elemental composition of ternary NCs beyond the use of In 3+ , which might otherwise provide important insight into their optical properties.…”

Optical spectroscopy reveals transition of CuInS2/ZnS to CuxZn1−xInS2/ZnS:Cu alloyed quantum dots with resultant double-defect luminescence

“…However, it should be noted that the detailed optical transitions involved in the defect-fluorescence of the CuInS 2 QDs are still under debate, and the mechanisms involve various defect-related radiative transitions including donor-acceptor pair transition, donor-valence band transition, and conduction-band-acceptor transition. [40][41][42] The very recent investigations show evidence that supports the model of photoluminescence by the radiative recombination of a conduction-band electron with a localized hole. 43,44 The limited information of our current study cannot give a decisive conclusion concerning this question.…”