Reversible photoluminescence quenching of CdSe/ZnS quantum dots embedded in porous glass by ammonia vapor

Dynamic Passivation in Perovskite Quantum Dots for Specific Ammonia Detection at Room Temperature

Perovskite structured CsPbX₃ (X = Cl, Br, or I) quantum dots (QDs) have attracted considerable interest in the past few years due to their excellent optoelectronic properties. Surface passivation is one of the main pathways to optimize the optoelectrical performance of perovskite QDs, in which the amino group plays an important role for the corresponding interaction between lead and halide. In this work, it is found that ammonia gas could dramatically increase photoluminescence of purified QDs and effectively passivate surface defects of perovskite QDs introduced during purification, which is a reversible process. This phenomenon makes perovskite QDs a kind of ideal candidate for detection of ammonia gas at room temperature. This QD film sensor displays specific recognition behavior toward ammonia gas due to its significant fluorescence enhancement, while depressed luminescence in case of other gases. The sensor, in turn-on mode, shows a wide detection range from 25 to 350 ppm with a limit of detection as low as 8.85 ppm. Meanwhile, a fast response time of ≈10 s is achieved, and the recovery time is ≈30 s. The fully reversible, high sensitivity and selectivity characteristics make CsPbBr₃ QDs ideal active materials for room-temperature ammonia sensing.

Porous flower-like superstructures based on self-assembled colloidal quantum dots for sensing

Quantum dots (QDs) have been envisaged as very promising materials for the development of advanced optical sensors. Here we report a new highly porous luminescent material based on colloidal QDs for potential applications in optical sensing devices. Bulk flower-like porous structures with sizes of hundreds of microns have been produced by slow destabilization of QD solution in the presence of a non-solvent vapor. The porous highly luminescent material was formed from CdSe QDs using the approach of non-solvent destabilization. This material demonstrated a 4-fold decrease in PL signal in the presence of the ammonia vapor. The relationship between the destabilization rate of QDs in solution and the resulting morphology of structural elements has been established. The proposed model of bulk porous flower-like nanostructured material fabrication can be applied to nanoparticles of different nature combining their unique properties. This research opens up a new approach to design novel multi-component composite materials enabling potential performance improvements of various photonic devices.

Influence of Ionizing Radiation and the Role of Thiol Ligands on the Reversible Photodarkening of CdTe/CdS Quantum Dots

We investigate the influence of high energy photons and thiol ligands on the photophysical properties of sub-monolayer CdTe/CdS quantum dots (QDs) immobilized in porous silica (PSiO2) scaffolds. The highly disperse, uniform distributions of QDs in a three-dimensional PSiO2 framework ensure uniform interaction of not only radiation but also subsequent surface repassivation solutions to all immobilized QDs. The high optical densities of QDs achieved using PSiO2 enable straightforward monitoring of the QD photoluminescence intensities and carrier lifetimes. Irradiation of QDs in PSiO2 by high energy photons, X-rays, and γ-rays leads to dose-dependent QD photodarkening, which is accompanied by accelerated photooxidative effects in ambient environments that give rise to blue-shifts in the peak QD emission wavelength. Irradiation in an oxygen-free environment also leads to QD photodarkening but with no accompanying blue-shift of the QD emission. Significant reversal of QD photodarkening is demonstrated following QD surface repassivation with a solution containing free-thiols, suggesting reformation of a CdS shell, etching of surface oxidized species, and possible reduction of photoionized dark QDs to a neutral, bright state. Permanent lattice displacement damage effects may contribute toward some irreversible γ radiation damage. This work contributes to an improved understanding of the influence of surface ligands on the optical properties of QDs and opens up the possibilities of engineering large area, low-cost, reuseable, and flexible QD-based optical radiation sensors.