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Two nanocomposites containing CdS nanoparticles in polymeric matrices were studied using the photoluminescence (PL) and optically detected magnetic resonance (ODMR) methods. Due to equal sizes of NPs in the composites (~5 nm) but different matrices – the oxygen-containing polymer PVA (polyvinyl alcohol) and oxygen-free polymer PEI (polyethyleneimine) – differences of nanocomposites properties are predominantly caused by different interfacial conditions. ODMR spectra have revealed five types of centers related to the PL emission – four centers involved in radiative recombination and one center related to non-radiative recombination processes. The oxygen-related interfacial center in CdS/PVA (LK1-center) and sulfur vacancy center in CdS/PEI (Vs-center) were identified.

Silver indium sulfide nanoparticles (NPs) stabilized in water by branched polyethyleneimine (PEI) were produced by a mild and direct synthesis. The Ag–In–S NPs exhibit relatively bright photoluminescence (PL) in the visible spectral range. The key parameters influencing color and intensity of PL are the Ag:In and Ag:S molar ratios and duration of the post-synthesis thermal treatment at ~100 °C. A maximal PL quantum yield, 20%, was observed for the Ag–In–S–PEI NPs produced at a molar Ag:In:S ratio of 1:5:5 and a thermal treatment at ~100 °C for 2 h. Such NPs are characterized by an average hydrodynamic size of around 100 nm. According to SEM each 100-nm globule comprises many smaller Ag–In–S NPs. Reasonably high PL quantum yield, variability of the emission color and self-aggregation of Ag–In–S–PEI NPs into polymer globules that do not scatter light makes such NPs promising for the luminescent bio-labeling applications. The PL band maximum energy of the Ag–In–S–PEI NPs produced in optimal conditions is very close to the band gap derived from the absorption spectra of colloidal solutions indicating that PL originates from the radiative recombination of delocalized or shallowly trapped charge carriers.

A direct “green” aqueous synthesis of mercapto acetate-stabilized copper indium sulfide (CIS) nanoparticles (NPs) and core/shell CIS@ZnS NPs of a varied composition under ambient conditions and a temperature lower than 100 °C is reported. The CIS@ZnS NPs can be anchored to the surface of nanocrystalline FTO/TiO2 films without additional purification or ligand exchange steps yielding visible-light-sensitive heterostructures ready for using as photoanodes in the liquid-junction solar cells. The highest photoelectrochemical activity in a three-electrode cell was demonstrated by a TiO2/CIS@ZnS heterostructure with atomic Cu : In : S and Zn : Cu ratios of 1 : 5 : 10 and 1 : 1. The optimized TiO2/CIS@ZnS photoanodes were tested in two-electrode solar cells with aqueous polysulfide electrolyte and TiO2/Cu2S heterostructures produced by a photo-assisted method as counter-electrodes. Under illumination by a 30 mW cm−2 xenon lamp, the optimized cells showed the average light conversion efficiency of 8.15%, the average open-circuit voltage of −0.6 V and the average fill factor of 0.42. The cells revealed excellent stability and reproducibility of photoelectrochemical parameters with around one percent variation of the light conversion efficiency around an average value for six identical solar cells.

A Raman spectroscopic study of Cu2ZnSnS4 (CZTS) nanocrystals (NCs) produced by a “green” synthesis in aqueous solutions is reported. Size-selected CZTS NCs reveal phonon confinement that manifests itself in an upward shift of the main phonon peak by about 3–4 cm−1 by varying the NC diameter from 3 to 2 nm. A non-monotonous shift and narrowing of the main peak are attributed to the special shape of the phonon dispersion in this material. Moreover, the method of sample preparation, the nature of the supporting substrate and the photoexcitation regime are found to crucially influence the Raman spectra of the CZTS samples. Particularly, the possible oxidation and hydrolysis of CZTS NCs with the concomitant formation of a Cu–S phase are systematically investigated. The nature of the film support is found to strongly affect the amount of admixture copper sulfide phases with the Cu2−xS/CuS content being the highest for oxidized silicon and glass and notably lower for ITO and even less for gold supports. The effect is assumed to originate from the different hydrophilicity of the supporting surfaces, resulting in a different morphology and surface area of the NC film exposed to the atmosphere, as well as the degree of the NC oxidation/hydrolysis. The amount of copper sulfide increases with the laser power. This effect is interpreted as a result of photochemical/photocatalytic transformations of the CZTS NCs.

Photocatalytic reduction of NaAuCl 4 by ethanol on the surface of mesoporous TiO 2 films illuminated by UV light results in the formation of nanocrystalline TiO 2 /Au heterostructures with an average size of gold nanoparticles varying in a range of 20−60 nm depending on the photoprocess conditions. Raman spectra of the TiO 2 /Au heterostructures excited in the surface plasmon resonance bands of the Au nanoparticles were obtained. The TiO 2 /Au films pre-illuminated with relatively high power density of the laser beam used in Raman experiment (100 W/cm 2 ) exhibit plasmonic enhancement of Raman scattering by titania excited subsequently with relatively low-intensity (10 W/cm 2 ) laser light. This effect sheds some light on the mechanistic aspects of plasmonic photocatalysis observed for many gold-based metal-semiconductor heterostructures.

The sulfidation of copper nanoparticles deposited onto ZnO surface by the photocatalytic reduction of Cu(II) results in the formation of ZnO/CuxS films that can be used as efficient counter electrodes in solar cells based on sulfide/polysulfide electrolytes. The films are formed by the spherical copper sulfide nano/micro-aggregates of tabulate CuxS nanoparticles with x = 1.3-1.4. A model cell with a FTO/ZnO/CdS photoanode produced by SILAR and FTO/ZnO/CuxS films as counter-electrode showed a light conversion efficiency, η = 1.73%, which is 25% higher than a similar cell where copper sulfide was deposited onto ZnO in "dark" conditions. Varying the conditions of the photocatalytic deposition of the starting copper nanoparticles slightly affects the electrocatalytic properties of the final FTO/ZnO/CuxS heterostructures.

The photocatalytic deposition of antimony(III) sulfide on the surface of TiO 2 films on the conductive FTO glass was investigated. The photoprocess yields particles of amorphous and almost stoichiometric Sb 2 S 3 with a size of 150–300 nm and spherical micrometer particles enriched with Sb with a Sb:S ratio that decreases gradually from 13:1 in the particle center to 5:1 at the surface. Thermal treatment of the FTO/TiO 2 /Sb 2 S 3 films at 350 °C results in the transformation of amorphous antimony(III) sulfide into crystalline stibnite without extensive changes in the film morphology. The crystalline FTO/TiO 2 /Sb 2 S 3 films exhibit photoelectrochemical activity when illuminated in the spectral range of λ > 350 nm in aqueous solutions of ascorbic acid as a sacrificial electron donor. The maximal photocurrent density generated by the TiO 2 /Sb 2 S 3 heterostructure is higher than the photoresponse of the starting FTO/TiO 2 film by a factor of 3.6. Deposition of an intermediary layer of In x (OH) y S z on the interface between TiO 2 and Sb 2 S 3 results in a further 3-fold increase in the photoelectrochemical activity of the FTO/TiO 2 /Sb 2 S 3 heterostructure.

Stable colloidal solutions of gold in water and ethanol were produced in the presence of small amounts of linear polyethyleneimine (PEI). In aqueous solutions a lowering of PEI concentration from 0.05 wt% to 0.0063 wt% results in an increase of the average size of Au particles from 3–7 nm to 30−40 nm. In ethanol 5–10 nm Au particles were produced in the presence of 0.0063–0.05 wt% PEI. At 0.05 wt% PEI the Au particles retain individual character but a lowering of PEI content to 0.0063 wt% causes particle aggregation into 80–140 nm globules. The Au–PEI nanoparticles exhibit catalytic activity in reduction of methylviologen bication to cation-radical by sulfide-ions as well as a co-catalyst of photocatalytic water reduction by ethanol with the participation of mesoporous TiO 2 . In both cases individual 4−8-nm Au–PEI particles show a much higher catalytic activity than 80−140-nm globules of aggregated Au–PEI NPs synthesized at a lower PEI content.

Photochemical activity of a semiconductor substance depends on a variety of different properties, including the spectral sensitivity range, band gap E g, positions (potentials) of the conduction band E CB and valence band E VB, mobility of photogenerated charge carriers and density of donor and acceptor states, surface morphology, adsorption capability, etc. Only a limited number of the reported semiconductors has a “complete” set of characteristics necessary for the photocatalytic action, mostly from the AIVBVI and AIIBVI groups. The photochemical activity was broadly reported for metal oxides (mostly TiO2, ZnO and rarely—WO3, Fe2O3, SnO2, Bi2O3, etc.), metal chalcogenides (most frequently—CdS, CdxZn1−xS, ZnS and rarely—CdSe, CdTe, In2S3, HgS, MoS2, etc.), and salts of metal based acids—metallates (for example, Na2Ti2O7, NaTaO3, SrTiO3, etc.). The photochemical activity of other semiconductors is reported much scarcely.

The photoelectrochemical light-harvesting systems constitute an important part of the assay of available solar light conversion approaches, along with the photovoltaic light conversion and endothermal photochemical reactions such as the hydrogen production, CO2 reduction, etc. [1–12]. Today, the realm of semiconductor-based solar cells is dominated (up to 85%) by “classic” photovoltaic systems based on single-crystal and polycrystalline silicon with a light conversion efficiency reaching 14–19 and 8–10%, respectively [2, 4, 12]. At the same time, a high price of the single-crystalline Si stimulates a search for alternative technologies based on more available materials, such as amorphous silicon, thin-film CdTe-based heterostructures [2, 12], organic conjugated polymers [2, 13–15], liquid-junction solar cells [2, 4–11], etc.

A strong interest to photochemical (photocatalytic, photoelectrochemical, and photoelectro-catalytic) processes with the participation of semiconductors was observed starting from 1970ths and resulted in the rise of semiconductor photochemistry as an independent discipline with exciting perspectives of applications in the chemical industrial synthesis, solar energy conversion, environmental protection, etc. [1–6]. The semiconductor photochemistry combined conceptions and knowledge of “classic” molecular photochemistry, catalysis, solid state physics, spectroscopy and other disciplines.

The studies of photochemical and photocatalytic processes involving the semiconductor NPs are performed using a broad range of modern physical and chemical methods applied to determine the NP size and structure, their spectral, photophysical and other properties. The most frequently used are electron spectroscopy in the absorption, transmission and reflection modes, photoluminescence spectroscopy, electron microscopy (in the scanning and transmission modes), X-rays diffraction, etc. Nuances of the photochemical properties of semiconductor NPs can be revealed using the lamp and laser flash photolysis, the electron paramagnetic resonance and the Raman spectroscopy. The voltammetry is often used to determine the potentials of conduction and valence bands of semiconductor NPs, the adsorption/desorption methods—for the determination of the specific surface are and pore size of semiconductor nanophotocatalysts. A detailed description of these methods is far beyond the scope of the present book. This chapter is confined to the methods using light to probe the properties of nanocrystalline semiconductors and thus shedding light on the structure and properties of these fascinating objects as a result of their interaction with the probing irradiation.

The research and development of new technologies for the conversion and storage of inexhaustible solar light energy were boosted several decades ago by the 1970th fuel crisis and a strategic need for sustainable power sources that can serve as alternatives to the fossil fuels. The basic idea was to accumulate the solar light energy as the electricity as well as to store it in the form of highly endothermic and eco-friendly fuels, in particular, molecular hydrogen produced by the photochemical splitting of water.

Semiconductor-based photocatalytic systems aimed at the reduction of carbon dioxide and dinitrogen are continuously studied for more than 30 years (Gratzel in Energy resources through photochemistry and catalysis. Academic Press, Inc., New York, 1983). A gradual shift from micro- to nanocrystalline semiconductor photocatalysts, which is, probably, the main trend in modern semiconductor photocatalysis/photoelectrochemistry, allowed to achieve attractively high quantum efficiencies of the CO2 and N2 conversion as well as to apply a potent array of spectral methods for the elucidation of mechanistic aspects of these important photoreactions. A decrease of the photocatalyst crystal size to a few nanometers allows not only to intensify the photocatalytic synthetic reactions but also to engineer the surface and band structure of the nano-photocatalysts to direct the reactions toward desirable products.

The first version of a manuscript on fine size selection of silver-indium-sulfide quantum dots prepared by a mild "green" method directly in aqueous solutions. The QDs were subjected to size-selective precipitation and their size-dependent structure, composition, optical and photoluminescence properties characterized. The paper has been recently submitted to Journal of Physical Chemistry.

Quenching of the photoluminescence of colloidal zinc oxide nanocrystals by a series of stable nitronyl nitroxide radicals was studied by means of stationary and time-resolved luminescence spectroscopy. Among the studied radicals the most efficient quenchers of the ZnO luminescence are the carboxyl-substituted species. The meta-substituted radical was found to be a more active quencher, than para-substituted one due to a closer proximity of the radical center to the nanocrystals surface. The PL quenching has a complex dynamic/static character. The dynamic quenching arises from photocatalytic radical reduction by ZnO conduction band electrons, while the static quenching is caused by adsorption of the photoreduction products on the nanocrystal surface. The non-substituted and OH-substituted radicals are inferior to the products of their photoreduction in capability of adsorption of the ZnO surface, and the quenching is dominated by interactions between the nanocrystals and photoreduced hydroxylamines. In case of COOH-substituted radicals, however, the radicals compete with the photoreduction products for the surface sites of ZnO nanocrystals resulting in a dynamic character of photoluminescence quenching.

Raman and infrared phonon spectra of ultrasmall (1.8 nm) colloidal CdS nanoparticles (usNPs) are presented. Multiphonon scattering by optical phonons up to the third order is observed in the Raman spectra at low temperature and resonant (325 nm) excitation. The first-order optical phonon peak is a superposition of several components, two of which can be assigned to surface optical (SO) and longitudinal optical (LO) modes, respectively. The LO mode, being markedly broadened compared to that of spectra of regular (>2 nm) NPs, is related to phonon confinement and bond distortion induced by a significant structural relaxation in usNPs. A shoulder observed above the LO frequency is either due to the density of phonon states induced by distorted surface bonds or due to higher-order scattering processes involving optical and acoustic phonons. The Raman peaks of usNPs do not reveal the upward shift and narrowing upon decreasing temperature from 300 K down to 85 K typical for crystalline semiconductors, even thoug...

Nanocrystalline FTO/ZnO/ZnSe were prepared from electrodeposited zinc oxide films and then converted into FTO/ZnO/CuSe heterostructures via complete substitution of zinc(II) in zinc selenide by copper(II). The starting FTO/ZnO films contain a 5–6-μm layer of porous zinc oxide microplatelets with the lateral size of up to 3 μm and the thickness of up to 200 nm which are formed by loosely aggregated ZnO nanocrystals. Partial conversion of such films into ZnSe and CuSe does not induce considerable changes in the film morphology allowing to use the FTO/ZnO films as a template defining the morphology and composition of resulting FTO/ZnO/ZnSe and FTO/ZnO/CuSe films. The FTO/ZnO/ZnSe heterostructures were found to be efficient photoanodes of model liquid-junction solar cells with sulfide/polysulfide redox-couple under illumination with white light ( λ > 400 nm). The activity of FTO/ZnO/CuSe heterostructures as cathodes of such solar cells was demonstrated for the first time. A two-electrode solar cell based on the FTO/ZnO/ZnSe photoanode and the FTO/ZnO/CuSe cathode generates by an order of magnitude higher photocurrent density as compared with a similar cell based on a Pt foil cathode.

Impregnation of the nanocrystalline TiO2 Degussa/Evonik P25 by colloidal graphene oxide produced by the Hummers method (H-GO) results in a 4-fold acceleration of photocatalytic gas-phase oxidation of ethanol and benzene vapors by air oxygen as a result of enhanced separation of the photogenerated charge carriers between TiO2 and H-GO. Preliminary photochemical reduction of H-GO decreases drastically its activity in ethanol photooxidation but does not affect appreciably photocatalytic oxidation of benzene. More deeply oxidized colloidal GO produced by the Brodie method (B-GO) almost does not affect the photocatalytic properties of titania in benzene photooxidation. It is concluded that the catalytic properties of GO in the photooxidation of ethanol and benzene depend on a balance between the capabilities of the GO sheets (i) to accept photoelectrons from titania nanocrystals and (ii) to bound to the TiO2 surface. The former factor depends on the aromaticity of GO particles and increases from B-GO to H-GO to photoreduced H-GO, while the latter factor depends on the density of the functional groups on GO sheets and increases in the opposite direction.

A comparative study of the temperature dependences of the photoluminescence (PL) of aqueous CdSe and silver-indium-sulfide (AIS) nanocrystals (NCs) in a broad range of 10–310 K is reported. Gelatin-incorporated CdSe (and core/shell CdSe/ZnS) NCs reveal both direct (excitonic) and trap-state-mediated PL components with different temperature dependences of the PL band maximum and spectral width. Glutathione-capped AIS (and core/shell AIS/ZnS) NCs emit a single broad PL band resembling the trap-related PL of CdSe NCs but showing nevertheless a temperature PL dependence typical for excitonic PL. In combination with previously reported results, these special features allow the PL emission of ternary AIS (AIS/ZnS) NCs to be explained based on the recombination of self-trapped excitons.

Properties of CdSe nanocrystals (NCs) fabricated in aqueous solutions at relatively mild conditions in the presence of gelatine and stabilized in polymer (gelatine, gelatine + polyvinylpyrrolidone, polyvinyl alcohol) matrices are characterized by Raman, optical absorption and photoluminescence spectroscopies. The effect of heating of the reaction mixture on the average NC size is discussed.

Nanocrystalline ITO/ZnO films formed by porous zinc oxide microplatelets 1–3 μm in size and 100–200 nm in thickness, which consist of 30–50 nm ZnO crystallites, were sensitized to visible light by Cd x Zn1−x S nanocrystals deposited using the method of successive ionic layer adsorption and reaction (SILAR). The composition of Cd x Zn1−x S nanocrystals as well as the dependence between molar Cd(II) fraction in the films and the ratio of cadmium and zinc nitrate concentrations in solutions used for the SILAR procedure were determined by a combination of electron, Raman, and energy-dispersive X-ray spectroscopies. The photovoltage observed at illumination of the ITO/ZnO/Cd x Zn1−x S heterostructures by white light (λ >400 nm) in aqueous Na2S solution increases with a decrease of Cd(II) content proportionally to an increment in the conduction band potential of the Cd x Zn1−x S nanocrystals. The photocurrent density normalized to the light absorbance of the ITO/ZnO/Cd x Zn1−x S films increases by a factor of around four when the conduction band potential of Cd x Zn1−x S nanocrystals grows by 220 mV as a result of Cd(II) fraction changing from 1.0 to 0.62–0.67. The results show that Cd x Zn1−x S solid solutions are more advantageous sensitizers for the short-wavelength part of the sensitivity window of the liquid-junction solar cells (400–450 nm) than conventionally used cadmium sulfide.

Mesoporous titania as powders and thin films on ITO were prepared using gelatin as an available and non-expensive pore-forming agent. The mesoporous TiO2 manifested a much higher photocatalytic activity in the gas-phase air oxidation of ethanol and acetaldehyde than the commercial nanocrystalline TiO2 P25 (Degussa Corp.). The mesoporous ITO/TiO2 films exhibited 12-14% efficiency of photocurrent generation in aqueous Na2S electrolyte when illuminated by UV light. Deposition of CdS and PbS nanoparticles onto the surface of ITO/TiO2 further increases the photocurrent yields and expands the light sensitivity range of the films to 500-520 nm (CdS) and to 650-700 nm (PbS).

Photochemical activity of colloidal graphene oxide in initiating of the acrylamide photopolymerization in aqueous solutions under the illumination with the visible light (λ > 420 nm) is reported for the first time. By photochemical activity graphene oxide occupies an intermediary place among typical visible-light-sensitive water-soluble photoinitiators of acrylamide polymerization. The photoinitiation involves photoexcited oxygen-containing functional groups of graphene oxide particles, the polymerization rate growing with an increase in the content of such functional groups and lowering drastically at their photoinduced elimination. The photopolymerization kinetics indicates the possibility of graphene oxide participation in the chain termination and shows that the aggregation of graphene oxide particles results in a decrease of their photochemical activity.

Spectral and photochemical properties of ZnO nanocrystal solutions containing free nitronyl nitroxide radical 2-(o-hydroxyphenyl)-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl (Nit(o-OH)Ph) were studied. The ZnO photoluminescence quenching by Nit(o-OH)Ph was observed and analysis of the dependences of ZnO photoluminescence intensity on radical concentrations revealed the prevalence of a static mechanism for this process. The changes in spectral properties of colloidal ZnO nanocrystal solutions in the presence of a Nit(o-OH)Ph radical under illumination were studied. The nitronyl nitroxide was found to undergo photoinduced reduction to the corresponding hydroxylamine both via the excited-state interaction with ethanol and capturing of the ZnO conduction band electrons. Photoreduction of the radical was observed under illumination with light of λ > 460 nm in the presence of 4.2 nm ZnO nanocrystals, while no changes took place in the case of larger 4.8 nm ZnO nanocrystals. This pronounced size effect was interpreted in terms of much stronger spatial exciton confinement in the smaller ZnO nanocrystals favouring the irreversible electron transfer from the photoexcited radical.

Colloidal β-In2S3 quantum dots stabilized in water by a number of polymers or sodium polyphosphate and mercaptoacetate were synthesized. An increase in the stabilizer content was found to result in a decrease in the average dot size from 20–30 to 5–10 nm and formation of a narrow absorption band centered at 290 nm. The position and spectral width of the band were found to be independent on stabilizer concentration, synthesis temperature and molar In:S ratio. The band was assumed to belong to a molecular cluster smaller than 1 nm which is a precursor for formation of larger regular indium sulfide quantum dots.

A green and mild synthesis of colloidal zinc oxide nanocrystals in ethanol/dimethylformamide mixtures was introduced which allows to produce stable crystalline ZnO particles and tailor their average size in the range of 2.8−4.5 nm by varying temperature and duration of post-synthesis ageing. An increase in dimethylformamide fraction in the mixture results in acceleration of ZnO nanocrystals ripening. Colloidal ZnO nanocrystals emit broadband photoluminescence in the range of 2−3 eV with the quantum yields of up to 12 %.

International audience; Nonresonant surface enhanced Raman scattering by opticalphonons of ZnO nanocrystals on and beneath silver and gold island films isreported. For both configurations comparable SERS efficiency is observed,proving their potential utility. Variations in peak intensities can beattributed to difference in the morphology of island films on and beneathnanocrystals as well as to variation of the interface between semiconductorand metal. The dominant peaks in the SERS spectra are assigned to surfaceoptical phonon modes.

We report on the synthesis and optical and structural characterization of ultrasmall (

The above-bandgap illumination of colloidal ZnO nanoparticles (NPs) in ethanol solutions is found to lead to reversible shifts of the absorption and photoluminescence (PL) excitation spectra, indicating charging of the nanoparticles with electrons. A rapid drop of deep-level PL intensity at the early stage of illumination is observed simultaneously with the splitting-off and growth of a new red-shifted near-band-edge PL band. Such a splitting of the near-bandgap PL band under illumination is observed for the first time and corroborates with the previous assumptions about the behavior of the NP ensemble emission upon gradual NPs’ charging with electrons. The possible relation between the new PL band and photoinduced charging of NPs with excess electrons is discussed on the basis of the dependence of the PL spectrum evolution and absorption band shift relaxation on the NP size and controllable access of oxygen during illumination.

Colloidal nanoparticles (NPs) of tetragonal β-In2S3 were stabilized in water and glycerol by mercaptoacetate anions. Doping of In2S3 NPs with AgI cations at the time of the synthesis imparts the NPs with the photoluminescence (PL) in the visible part of the spectrum. The doping results also in a shift of the absorption threshold and the PL band maximum to longer wavelengths proportional to the AgI content. The PL band maximum of AgI-doped In2S3 NPs can be varied from 575–580 to 760–765 nm by augmenting the silver(I) amount and the duration and temperature of the post-synthesis aging. The average radiative life-time of AgI-doped In2S3 NPs also depends on the silver(I) content and reaches the maximal value, 960 ns, at a molar Ag:In ratio of 1:4. The maximal quantum yield of stationary PL, 12 %, is observed at this Ag:In ratio as well. Deposition of a ZnS “shell” on the surface of AgI-doped In2S3 NPs results in an increase of the PL quantum yield to ~30 %.

The 2–3 nm size-selected glutathione-capped Ag–In–S (AIS) and core/shell AIS/ZnS quantum dots (QDs) were produced by precipitation/redissolution from an aqueous colloidal ensemble. The QDs reveal broadband photoluminescence (PL) with a quantum yield of up to 60% for the most populated fraction of the core/shell AIS/ZnS QDs. The PL band shape can be described by a self-trapped exciton model implying the PL band being a sequence of phonon replica of a zero-phonon line resulting from strong electron–phonon interaction and a partial conversion of the electron excitation energy into lattice vibrations. It can be concluded that the position and shape of the PL bands of AIS QDs originate not from energy factors (depth and distribution of trap states) but rather from the dynamics of the electron–phonon interaction and the vibrational relaxation in the QDs. The rate of vibrational relaxation of the electron excitation energy in AIS QDs is found to be size-dependent, increasing almost twice from the largest to the ...

Ternary luminescent copper and silver indium sulfide quantum dots (QDs) can be an attractive alternative to cadmium and lead chalcogenide QDs. The optical properties of Cu-In-S and Ag-In-S (AIS) QDs vary over a broad range depending on the QD composition and size. The implementation of ternary QDs as emitters in bio-sensing applications can be boosted by the development of mild and reproducible syntheses directly in aqueous solutions as well as the methods of shifting the photoluminescence (PL) bands of such QDs as far as possible into the near IR spectral range. In the present work, the copper-doping of aqueous non-stoichiometric AIS QDs was found to result in a red shift of the PL band maximum from around 630 nm to ∼780 nm and PL quenching. The deposition of a ZnS shell results in PL intensity recovery with the highest quantum yield of 15%, with almost not change in the PL band position, opposite to the undoped AIS QDs. Size-selective precipitation using 2-propanol as a non-solvent allows discrimination of up to 9 fractions of Cu-doped AIS/ZnS QDs with the average sizes in the fractions varying from around 3 to 2 nm and smaller and with reasonably the same composition irrespective of the QD size. The decrease of the average QD size results in a blue PL shift yielding a series of bright luminophors with the emission color varies from deep-red to bluish-green and the PL efficiency increases from 11% for the first fraction to up to 58% for the smallest Cu-doped AIS/ZnS QDs. The rate constant of the radiative recombination of the size-selected Cu-doped AIS/ZnS QDs revealed a steady growth with the QD size decrease as a result of the size-dependent enhancement of the spatial exciton confinement. The copper doping was found to result in an enhancement of the photoelectrochemical activity of CAIS/ZnS QDs introduced as spectral sensitizers of mesoporous titania photoanodes of liquid-junction solar cells.

Ultrasmall (∼2 nm) copper(I)- and silver(I)-doped CdS and core/shell CdSe/CdS quantum dots (QDs) stabilized by Cd(II) complexes with mercaptoacetate anions and ammonia were produced in aqueous solu...

The paper reviews the state of the art in the synthesis of multinary (ternary, quaternary and more complex) metal chalcogenide nanocrystals (NCs) and their applications as a light absorbing or an auxiliary component of light-harvesting systems. This includes solid-state and liquid-junction solar cells and photocatalytic/photoelectrochemical systems designed for the conversion of solar light into the electric current or the accumulation of solar energy in the form of products of various chemical reactions. The review discusses general aspects of the light absorption and photophysical properties of multinary metal chalcogenide NCs, the modern state of the synthetic strategies applied to produce the multinary metal chalcogenide NCs and related nanoheterostructures, and recent achievements in the metal chalcogenide NC-based solar cells and the photocatalytic/photoelectrochemical systems. The review is concluded by an outlook with a critical discussion of the most promising ways and challenging aspects of further progress in the metal chalcogenide NC-based solar photovoltaics and photochemistry.