Quantum dot (QD) solids represent a new type of condensed matter drawing high fundamental and applied interest. Quantum confinement in individual QDs, combined with macroscopic scale whole materials, leads to novel exciton and charge transfer features that are particularly relevant to optoelectronic applications. This Perspective discusses the structure of semiconductor QD solids, optical and spectral properties, charge carrier transport, and photovoltaic applications. The distance between adjacent nanoparticles and surface ligands influences greatly electrostatic interactions between QDs and, hence, charge and energy transfer. It is almost inevitable that QD solids exhibit energetic disorder that bears many similarities to disordered organic semiconductors, with charge and exciton transport described by the multiple trapping model. QD solids are synthesized at low cost from colloidal solutions by casting, spraying, and printing. A judicious selection of a layer sequence involving QDs with different size, composition, and ligands can be used to harvest sunlight over a wide spectral range, leading to inexpensive and efficient photovoltaic devices.

Variation of the steady-state optical properties of quantum dots (QDs) caused by photoinduced charge transfer is a widely known phenomenon which hinders QD applications requiring long-term stability of the optical signal, for example, bioimaging, singlephoton sources, molecular tracking, and lasing. Intense light irradiation may provoke QD photodarkening, when their photoluminescence (PL) quantum yield (QY) is reduced, or photobrightening, when the QY increases and QD PL becomes brighter. In order to understand the nature of these processes and to determine the optimal operating conditions for QDs with different core sizes and shell thicknesses, we have systematically studied the photodarkening and photobrightening phenomena for different wavelengths and intensities of irradiation. The results have shown that changes in the core size only slightly alter the effect of light irradiation on the QD optical properties, whereas the irradiation wavelength and shell thickness are the major factors that determine the variation of the QD PL QY. We have found that the observed photoinduced processes are independent of the irradiation intensity, which proves the single-photon origin of these processes. We have also used comparative data on irradiation of QD solution and QDs embedded in polymer matrices to develop a general model describing the mechanism of the QD sensitivity to intense irradiation and elucidating the role of surface ligands in this mechanism. Our findings determine the strategy for increasing QD optical stability and optimization of operational conditions for QD-based devices.

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Ion mobility spectrometry instrumentation today is widespread in the area of transport security and counterterrorism. This method of detection of explosive substances is highly appreciated for the existence of portable detectors capable of detecting concentrations of 10−13–10−14 g/cm3 at atmospheric pressure using traditional ionization methods including corona discharge and beta radiation. However, low vapor pressure of some explosives imposes requirements on limit of detection (LOD) down to 10–15‒10−16 g/cm3. In this paper we compare a radioactive 63Ni ionization source with a laser ionization source and reveal the parameters of laser ionization of a group of explosives, namely trinitrotoluene (TNT), cyclotrimethylene-trinitramine (RDX), cyclotetramethylene-tetranitramine (HMX) and pentaerythritol tetranitrate (PETN), which can reduce the limit of detection of portable devices. A laser ionization source can provide a higher signal to noise ratio than radioactive 63Ni at optimal intensity of laser radiation for PETN and HMX of 3 × 107 W/cm2 and 2.5 × 107 W/cm2, respectively. Limits of detection were estimated: 3 × 10−15 g/cm3 for RDX, 8 × 10−15 g/cm3 for PETN and less than 3 × 10−15 g/cm3 for HMX. These results are promising to further improve the capabilities of detectors of low volatility explosives without sacrificing portability, light weight and reasonable cost of the laser source.

Controlling spontaneous emission by modifying the local electromagnetic environment is of great interest for applications in optoelectronics, biosensing and energy harvesting. Although the development of devices based on one-dimensional porous silicon photonic crystals with embedded luminophores is a promising approach for applications, the efficiency of the embedded luminophores remains a key challenge because of the strong quenching of the emission due to the contact of the luminophores with the surface of porous silicon preventing the observation of interesting light–matter coupling effects. Here, we experimentally demonstrate an increase in the quantum dot (QD) spontaneous emission rate inside a porous silicon microcavity and almost an order of magnitude enhancement of QD photoluminescence intensity in the weak light–matter coupling regime. Furthermore, we have demonstrated drastic alteration of the QD spontaneous emission at the edge of the photonic band gap in porous silicon distributed Bragg reflectors and proved its dependence on the change in the density of photonic states.

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A method for targeted variation of the radiation properties of quantum dots (QDs) to control the efficiency of resonance energy transfer in nanocrystal assemblies and nano-bio hybrid materials has been developed. The method is based on strong ultraviolet (UV) laser irradiation of QDs and allows the extinction and luminescence spectra to be controlled and the luminescence quantum yield and decay kinetics to be varied. Water-soluble QDs have been synthesized and used for analyzing the effect of energy transfer from semiconductor nanocrystals on the photocycle of the photosensitive protein bacteriorhodopsin (bR) in bR–QD complexes. The UV irradiation mode has been selected in a way permitting the modulation of QD optical parameters without modification of their structure or physico-chemical properties. It is concluded that the QD interaction with bR accelerates its photocycle, but this acceleration is determined by electrostatic interactions, rather than Förster resonance energy transfer from QDs to bR. The method of UV laser irradiation of fluorescent semiconductor QDs has proven to be an efficient technique for variation of nanocrystal optical properties without affecting their structure, as well as for fine modulation of the energy transfer processes in the nanocrystal assemblies and nano-bio hybrid materials.

Although porous silicon (pSi) was first obtained in the mid-20th century, considerable interest in this material arose much later, due to the discovery of its room-temperature photoluminescence (PL). In the 1990s, most studies on pSi were focused on the analysis and explanation of its photoluminescent and electroluminescent characteristics and their potential practical applications. The latest advances in pSi research are related to its biocompatibility and biomedical applications. The discovery of singlet oxygen generation by pSi through nonradiative transfer of photoexcitation energy has opened new prospects for photodynamic therapy in vivo, and the discovery of laser desorption/ionization on pSi has paved the way for advanced approaches in mass-spectrometry. In this study, the main photophysical properties of pSi are reviewed, and a wide range of photo-processes characteristic of pSi and their practical implications are analyzed in terms of the general principles of energy and charge transfer. Special attention is paid to the possible applications of pSi and pSi-based nanocomposites in photonics, biophysics, medicine, and analytical chemistry.