On the origin of stretched exponential (Kohlrausch) relaxation kinetics in the room temperature luminescence decay of colloidal quantum dots

Ermolaev V.L.

Data on the influence of deuteration of organic molecules and/or solvent on their fluorescence quantum yield are summarized. It is demonstrated that the effect of deuteration is normal, i.e., deuteration increases the fluorescence quantum yield due to decrease in the internal conversion probability, for organic molecules exhibiting fluorescence in the red region of spectrum, in which the internal conversion competes with the emission of fluorescence. In the case in which the probability of internal conversion is low, i.e., energy of level S1 ≥ 16000–20000 cm–1, the intersystem crossing probability from the S1 state to the set of triplet levels depends on the relative position of S1 and the nearest triplet level. In so doing, the effect of deuteration can be either normal or anomalous, depending on whether the resonance between the S1 level and the level nearest to it, the Tn level, improves or deteriorates when these levels shift as a result of deuteration. In dilute vapors, cooled supersonic jets, and crystalline matrices, including Shpolskii matrices, the effect of deuteration at helium temperatures depends on exact resonance between the interacting levels. In the case of dilute vapors and cooled jets, the effect also depends on the vibronic level being excited. Deuteration of OH and NH groups, as a rule, slows proton transfer in the S1 state of the molecule that occurs with their involvement, leading to normal effect of deuteration.

Pietryga J.M., Park Y., Lim J., Fidler A.F., Bae W.K., Brovelli S., Klimov V.I.

The field of nanocrystal quantum dots (QDs) is already more than 30 years old, and yet continuing interest in these structures is driven by both the fascinating physics emerging from strong quantum confinement of electronic excitations, as well as a large number of prospective applications that could benefit from the tunable properties and amenability toward solution-based processing of these materials. The focus of this review is on recent advances in nanocrystal research related to applications of QD materials in lasing, light-emitting diodes (LEDs), and solar energy conversion. A specific underlying theme is innovative concepts for tuning the properties of QDs beyond what is possible via traditional size manipulation, particularly through heterostructuring. Examples of such advanced control of nanocrystal functionalities include the following: interface engineering for suppressing Auger recombination in the context of QD LEDs and lasers; Stokes-shift engineering for applications in large-area luminescent solar concentrators; and control of intraband relaxation for enhanced carrier multiplication in advanced QD photovoltaics. We examine the considerable recent progress on these multiple fronts of nanocrystal research, which has resulted in the first commercialized QD technologies. These successes explain the continuing appeal of this field to a broad community of scientists and engineers, which in turn ensures even more exciting results to come from future exploration of this fascinating class of materials.

McClymont D., Teh I., Carruth E., Omens J., McCulloch A., Whittington H.J., Kohl P., Grau V., Schneider J.E.

The diffusion tensor model assumes Gaussian diffusion and is widely applied in cardiac diffusion MRI. However, diffusion in biological tissue deviates from a Gaussian profile as a result of hindrance and restriction from cell and tissue microstructure, and may be quantified better by non-Gaussian modeling. The aim of this study was to investigate non-Gaussian diffusion in healthy and hypertrophic hearts.Thirteen rat hearts (five healthy, four sham, four hypertrophic) were imaged ex vivo. Diffusion-weighted images were acquired at b-values up to 10,000 s/mm2 . Models of diffusion were fit to the data and ranked based on the Akaike information criterion.The diffusion tensor was ranked best at b-values up to 2000 s/mm2 but reflected the signal poorly in the high b-value regime, in which the best model was a non-Gaussian "beta distribution" model. Although there was considerable overlap in apparent diffusivities between the healthy, sham, and hypertrophic hearts, diffusion kurtosis and skewness in the hypertrophic hearts were more than 20% higher in the sheetlet and sheetlet-normal directions.Non-Gaussian diffusion models have a higher sensitivity for the detection of hypertrophy compared with the Gaussian model. In particular, diffusion kurtosis may serve as a useful biomarker for characterization of disease and remodeling in the heart. Magn Reson Med 78:1174-1186, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Leng H., Loy J., Amin V., Weiss E.A., Pelton M.

This Letter reports the measurement of photoinduced electron-transfer rates from individual CdSe/CdS nanocrystals, or quantum dots (QDs), to methyl viologen acceptor molecules adsorbed on the QD surfaces, using time-resolved photoluminescence at the single-nanocrystal level. For each QD measured, the electron-transfer rate is constant over time, and the photoluminescence blinking dynamics are independent of the measured transfer rate. The total electron-transfer rate is distributed in discrete, constant increments, corresponding to discrete numbers of adsorbed molecules on each QD. The results thus validate previous assumptions that viologen molecules adsorb independently on QD surfaces and that the total electron-transfer rate from a single QD to multiple molecules on its surface is simply the sum of the transfer rates to the individual molecules. The measurement provides an optical method to count the number of active acceptor molecules bound to a single nanocrystal and opens up new possibilities for me...

Guo X., Smedskjaer M.M., Mauro J.C.

Understanding nonequilibrium glassy dynamics is of great scientific and technological importance. However, prediction of the temperature, thermal history, and composition dependence of nonequilibrium viscosity is challenging due to the noncrystalline and nonergodic nature of the glassy state. Here, we show that the nonequilibrium glassy dynamics are intimately connected with the equilibrium liquid dynamics. This is accomplished by deriving a new functional form for the thermal history dependence of nonequilibrium viscosity, which is validated against experimental measurements of industrial silicate glasses and computed viscosities for selenium over a wide range of conditions. Since the temperature and composition dependence of liquid viscosity can be predicted using temperature-dependent constraint theory, our work also opens the possibility to improve understanding of the physics of nonequilibrium viscosity.

Piland G.B., Huang Z., Lee Tang M., Bardeen C.J.

The combination of CdSe semiconductor nanocrystals with 9-anthracene carboxylic acid ligands can sensitize triplet–triplet annihilation on the emitter molecule diphenylanthracene. This hybrid system has recently been shown to upconvert visible light (532 nm) to ultraviolet light (420 nm) (Huang, Z., et al. Nano Lett. 2015, 15, 5552–5557). In the current paper, time-resolved photoluminescence measurements are used to characterize the kinetics of the energy transfer from the CdSe exciton state to the triplet state of the anthracene ligand. We find that 9-anthracene carboxylic acid binds to CdSe according to Poisson statistics with a maximum number of 2–3 ligands per nanocrystal. The CdSe-to-ligand energy transfer rate is 1.5 × 107 s–1. The overall efficiency of the energy transfer appears to be limited by the presence of fast nonradiative decay channels in the nanocrystals and the low coverage of anthracene ligands, resulting from the specific ligand exchange conditions used in this paper. Possible strategi...

Bodunov E.N., Danilov V.V., Panfutova A.S., Simões Gamboa A.L.

Kaiser U., Sabir N., Carrillo-Carrion C., del Pino P., Bossi M., Heimbrodt W., Parak W.J.

Manganese-doped CdS/ZnS quantum dots have been used as energy donors in a Förster-like resonance energy transfer (FRET) process to enhance the effective lifetime of organic fluorophores. It was possible to tune the effective lifetime of the fluorophores by about six orders of magnitude from the nanosecond (ns) up to the millisecond (ms) region. Undoped and Mn-doped CdS/ZnS quantum dots functionalized with different dye molecules were selected as a model system for investigating the multiple energy transfer process and the specific interaction between Mn ions and the attached dye molecules. While the lifetime of the free dye molecules was about 5 ns, their linking to undoped CdS/ZnS quantum dots led to a long effective lifetime of about 150 ns, following a non-exponential transient. Manganese-doped core-shell quantum dots further enhanced the long-lasting decay time of the dye to several ms. This opens up a pathway to analyse different fluorophores in the time domain with equal spectral emissions. Such lifetime multiplexing would be an interesting alternative to the commonly used spectral multiplexing in fluorescence detection schemes.

Bain D., Paramanik B., Sadhu S., Patra A.

Metal cluster-semiconductor nanocomposite materials remain a frontier area of research for the development of optoelectronic, photovoltaic and light harvesting devices because metal nanoclusters and semiconductor QDs are promising candidates for photon harvesting. Here, we have designed well defined metal cluster-semiconductor nanostructures using different surface capped negatively charged Au25 nanoclusters (Au NCs) and positively charged cysteamine capped CdTe quantum dots using electrostatic interactions. The main focus of this article is to address the impact of surface capping agents on the photophysical properties of Au cluster-CdTe QD hybrid nanocomposites. Steady state and time resolved spectroscopic studies reveal that photoluminescence quenching, radiative and nonradiative rate, and energy transfer between Au nanoclusters and CdTe QDs have been influenced by the nature of the capping agent. We have calculated the energy transfer related parameters such as the overlap integral, distance between donor and acceptor, Förster distance, efficiency of energy transfer and rate of energy transfer from CdTe QDs to three different Au NCs. Photoluminescence quenching varies from 73% to 43% when changing the capping agents from bovine serum albumin (BSA) to glutathione (GSH). The efficiency of the energy transfer from CdTe QDs to BSA-capped Au NCs is found to be 83%, for Cys-capped Au NCs it was 46% and for GSH-capped Au NCs it was 35%. The efficiency depends on the number of Au clusters attached per QD. This reveals that the nature of capping ligands plays a crucial role in the energy transfer phenomena from CdTe QDs to Au NCs. Interesting findings reveal that the efficient energy transfer in metal cluster-semiconductor nanocomposites may open up new possibilities in designing artificial light harvesting systems for future applications.

Liu F., Rodina A.V., Yakovlev D.R., Golovatenko A.A., Greilich A., Vakhtin E.D., Susha A., Rogach A.L., Kusrayev Y.G., Bayer M.

We present a systematic experimental study along with theoretical modeling of the energy transfer in an ensemble of closely-packed CdTe colloidal nanocrystals identified as the F\"orster resonant energy transfer (FRET). We prove that at low temperature of 4.2 K, mainly the ground dark exciton states in the initially excited small-size (donor) nanocrystals participate in the dipole-dipole FRET leading to additional excitation of the large-size (acceptor) nanocrystals. The FRET becomes possible due to the weak admixture of the bright exciton states to the dark states. The admixture takes place even in zero magnetic field and allows the radiative recombination of the dark excitons. An external magnetic field considerably enhances this admixture, thus increasing the energy transfer rate by a factor of 2-3 in a field of 15T, as well as the radiative rates of the dark excitons in the donor and acceptor nanocrystals. The theoretical modeling allows us to determine the spectral dependence of the probability for the NC to serve as a donor for larger nanocrystals, to evaluate the energy transfer rates as well as to predict their dependencies on the magnetic field, to describe the spectral shift of the photoluminescence maximum due to the energy transfer and to reproduce the experimentally observed spectral dependencies of the photoluminescence recombination dynamics in the magnetic field.

Bodunov E.N., Berberan-Santos M.N.

The kinetics of the luminescence concentration depolarization of molecules in a medium is studied theoretically. It is shown that the concentration depolarization kinetics is well described by a stretched exponential function of time, r(t)/r 0 ≈ exp[−b(t/τ)β], where r(t) and r 0 are the luminescence anisotropy values at time moments t and t = 0, respectively. The parameters b and β allow the determinnation of the penetration depth of the molecules in the medium.

Ji X., Makarov N.S., Wang W., Palui G., Robel I., Mattoussi H.

We explored the charge transfer interactions between CdSe–ZnS core–shell quantum dots (QDs) and the redox active neurotransmitter dopamine, using covalently assembled QD–dopamine conjugates. We combined steady-state fluorescence, time-resolved fluorescence, and transient absorption bleach measurements to probe the effects of changing the QD size (thus the QD energy levels) and the conjugate valence on the rate of QD photoluminescence quenching when the pH of the medium was adjusted from acidic to alkaline. We measured substantially larger quenching efficiencies, combined with more pronounced shortening of the carrier dynamics of these assemblies for smaller size QDs and in alkaline pH. Moreover, we found that changes in the QD size alter the electron and hole relaxation of photoexcited QDs but with different extents. For instance, a pronounced change in the hole relaxation was measured in alkaline buffers. Moreover, the hole relaxation was faster for conjugates of green-emitting QDs as compared to their r...

Kaiser U., Jimenez de Aberasturi D., Vázquez-González M., Carrillo-Carrion C., Niebling T., Parak W.J., Heimbrodt W.

Semiconductor quantum dots functionalized with organic dye molecules are important tools for biological sensor applications. Energy transfer between the quantum dot and the attached dyes can be utilized for sensing. Though important, the determination of the real number of dye molecules attached per quantum dot is rather difficult. In this work, a method will be presented to determine the number of ATTO-590 dye molecules attached to CdSe/ZnS quantum dots based on time resolved spectral analysis. The energy transfer from the excited quantum dot to the attached ATTO-590 dye leads to a reduced lifetime of the quantum dot's excitons. The higher the concentration of dye molecules, the shorter the excitonic lifetime becomes. However, the number of dye molecules attached per quantum dot will vary. Therefore, for correctly explaining the decay of the luminescence upon photoexcitation of the quantum dot, it is necessary to take into account the distribution of the number of dyes attached per quantum dot. A Poisson distribution of the ATTO-590 dye molecules not only leads to excellent agreement between experimental and theoretical decay curves but also additionally yields the average number of dye molecules attached per quantum dot. In this way, the number of dyes per quantum dot can be conveniently determined.

Litvin A.P., Parfenov P.S., Ushakova E.V., Simões Gamboa A.L., Fedorov A.V., Baranov A.V.

The analysis of the steady-state and transient photoluminescence (PL) of PbS quantum dots (QDs) of diameter in the 3.2–6.9 nm range in porous matrixes at temperatures 77–300 K shows that QDs of different sizes possess entirely different temperature dependencies of their PL properties. The data indicates the presence of two emissive “in-gap” states in the low-energy electronic structure of the QDs with characteristic dependencies on QD size and temperature. The lowest energy state is associated with surface defect states while the higher energy state is “intrinsic” and arises due to size-dependent splitting of the lowest excitons.

Mauro J.C., Smedskjaer M.M.

The field of glass science is quickly maturing from a purely empirical science to one built upon rigorous fundamental physics. These advancements offer an unprecedented level of understanding of the glass transition and the glassy state, as well as the ability to design new glass compositions starting at the atomic level. As a nonequilibrium material, the structure and properties of glass depend not only on its composition, but also on its thermal and pressure histories. Since glass is thermodynamically unstable, it is continually relaxing toward the metastable supercooled liquid state. Owing to this time dependence of glass properties and microstructure, traditional reversible thermodynamics cannot be directly applied to study the glassy state. While some nonequilibrium aspects of the glassy state can be estimated using irreversible thermodynamics, this approach has no microscopic basis and hence cannot offer a rigorous physical description of either the glass transition or glass itself. Alternatively, nonequilibrium statistical mechanics offers a framework in which the macroscopic properties of a glass can be rigorously calculated from its microscopic structure. As such, statistical mechanics has many practical applications in glass science and technology. The objective of this article is to provide an overview of various statistical mechanical descriptions of the glassy state and their practical use in understanding glass physics and in the design of new glass compositions. The relationship among these various descriptions is emphasized to build a single unified picture of glass statistical mechanics synthesizing these various approaches.

Liu Y., Fan Z., Li R., Mavrič A., Arčon I., Valant M., Kapun G., Zhang B., Feng C., Zhang Z., Chen T., Zhang Y., Li Y.

Chou K., Zeitz D.C., Khvichia M., Barnett J.L., Zhang J.Z.

Xie H., Jin B., Luo P., Zhou Q., Yang D., Zhang X.

Khvichia M., Chou K., Lee S., Zeitz D.C., Zou S., Li Y., Zhang J.Z.

We have synthesized L-cysteine and oleylamine stabilized CsPbBr3 perovskite quantum dots (PQDs) and coupled them with gold nanoparticles (AuNPs). The PQDs and AuNPs, as well as their hybrid nanostructures (HNS), were characterized using UV–visible (UV–vis) and photoluminescence (PL) spectroscopy. The UV–vis spectra show absorption bands of the HNS at 503 and 520 nm, attributed mainly to PQDs and AuNPs, respectively. The PQDs show a strong excitonic PL band peaked at 513 nm from PQDs. The HR-TEM results show the formation of hybrid structures between PQDs and AuNPs, which is also supported by the PL quenching of the PQDs by the coupled AuNPs. Ultrafast dynamics of the exciton and charge carriers in the HNS and pristine PQD were studied using femtosecond transient absorption. Multiexponential fitting of the dynamic data revealed the existence of shallow and deep trap states in pristine PQDs and ultrafast electron transfer from PQDs to AuNPs in the HNS. A kinetic model was proposed to account for the key dynamic processes involved and to extract the time for electron transfer from PQDs to AuNPs in the HNS, found to be ∼2 ps. Dynamic processes in pristine PQDs are largely unchanged by HNS formation with AuNPs.

Taimori A., Mills B., Gaughan E., Ali A., Dhaliwal K., Williams G., Finlayson N., Hopgood J.R.

Cho K., Park Y., Jo H., Seo S., Moon J., Lee S.J., Park S.Y., Yoon S.J., Park J.

Rempel Andrey A., Ovchinnikov Oleg V., Weinstein Ilya A., Rempel Svetlana V., Kuznetsova Yulia V., Naumov Andrei V., Smirnov Mikhail S., Eremchev Ivan Yu., Vokhmintsev Alexander S., Savchenko Sergey S.

Quantum dots are the most exciting representatives of nanomaterials. They are synthesized using advanced methods of nanotechnology pertaining to both inorganic and organic chemistry. Quantum dots possess unique physical and chemical properties; therefore, they are used in very different fields of physics, chemistry, biology, engineering and medicine. It is not surprising that the Nobel Prize in chemistry in 2023 was given for discovery and synthesis of quantum dots. This review addresses modern methods for the synthesis of quantum dots and their optical properties and practical applications. In the beginning, a short insight into the history of quantum dots is given. Many gifted scientists, including chemists and physicists, were engaged in these studies. The synthesis of quantum dots in solid and liquid matrices is described in detail. Quantum dots are well-known owing to their unique optical properties; that is why the attention in the review is focused on the quantum-size effect. The causes for fascinating blinking of quantum dots and techniques for observation of a single quantum dot are considered. The last part of the review describes mportant applications of quantum dots in biology, medicine and quantum technologies.The bibliography includes 772 references.

Baldacchini G., Lattanzi A.

Abstract Photoluminescence (PL) degradation of thermally evaporated Alq3 thin films is described by four Kohlrausch-Williams-Watt (KWW) functions, which are solely mathematical expressions. The present contribution not only unfolds the physical meaning of the KWW function, but also reveals new mathematical tools. By introducing the concept of the material clock, the system has been described by a damped harmonic oscillator, which in certain conditions allows the expansion of the KWW function in the so-called Prony series. The terms of this series can be attributed to chemical and physical processes that contribute to the decay, i.e., the degradation, of the Alq3 thin films when interacting with internal and environmental agents. These insights unveiled the usefulness of proper mathematical procedures and properties, such as the monotonicity and the complete monotonicity, for investigating the PL of this ubiquitous organometallic molecule, which possesses one among the highest emission yield. Moreover, this method is also promising for describing the photoluminescent processes of similar organic molecules important both for basic research and optoelectronic applications.

Akhuli A., Preeyanka N., Chakraborty D., Sarkar M.

Understanding the fundamentals behind the photophysical response of a fluorescing species in the vicinity of plasmonic nanoparticles is of great interest due to the importance of this event in various applications.

Clabel H. J.L., Lozano C. G., Pinto I.C., Falci R.F., Rivera V.A., Messaddeq Y., Marega E.

This chapter is a review dedicated to recent advances in the science of glassGlass and its applicationApplications in photonic devicesPhotonic device with a straightforward, easy-to-read style. It is important to mention as a starting point that recent advances in this material indicate that the glassGlass networkNetwork has significant implications both in terms of the opticalOptical and mechanical propertiesMechanical properties and, therefore, the functionalities of glassGlass as a smart material. In this sense, it is essential for the development of new technologiesTechnology or innovations to better understand the effects of manufacturing techniques to achieve the desired product. In this context, we provide an overview of the history and challenges in glassGlass development, traditional and new manufacturing processes, characterization techniques (structuralStructural, thermalThermal, and optical propertiesOptical properties), glassesGlass family, and photonic devicePhotonic device applicationsApplications.

Martins J.R., Krivenkov V., Bernardo C.R., Samokhvalov P., Nabiev I., Rakovich Y.P., Vasilevskiy M.I.

Simões Gamboa A.L., Bodunov E.N.

We briefly review functions that we have proposed for the description of the experimentally observed nonexponential photoluminescence (PL) decay kinetics of colloidal quantum dots (QDs) at room temperature (RT) with parameters that have a straightforward physical meaning.

Nielsen C.L., Turtos R.M., Bondesgaard M., Nyemann J.S., Jensen M.L., Iversen B.B., Muren L.P., Julsgaard B., Balling P.

Radiotherapy is a well-established and important treatment for cancer tumors, and advanced technologies can deliver doses in complex three-dimensional geometries tailored to each patient's specific anatomy. A 3D dosimeter, based on optically stimulated luminescence (OSL), could provide a high accuracy and reusable tool for verifying such dose delivery. Nanoparticles of an OSL material embedded in a transparent matrix have previously been proposed as an inexpensive dosimeter, which can be read out using laser-based methods. Here, we show that Cu-doped LiF nanocubes (nano-LiF:Cu) are excellent candidates for 3D OSL dosimetry owing to their high sensitivity, dose linearity, and stability at ambient conditions. We demonstrate a scalable synthesis technique producing a material with the attractive properties of a single dosimetric trap and a single near-ultraviolet emission line well separated from visible-light stimulation sources. The observed transparency and light yield of silicone sheets with embedded nanocubes hold promise for future 3D OSL-based dosimetry.

Fu J., Fan Z., Nakabayashi M., Ju H., Pastukhova N., Xiao Y., Feng C., Shibata N., Domen K., Li Y.

Interface engineering is a proven strategy to improve the efficiency of thin film semiconductor based solar energy conversion devices. Ta3N5 thin film photoanode is a promising candidate for photoelectrochemical (PEC) water splitting. Yet, a concerted effort to engineer both the bottom and top interfaces of Ta3N5 thin film photoanode is still lacking. Here, we employ n-type In:GaN and p-type Mg:GaN to modify the bottom and top interfaces of Ta3N5 thin film photoanode, respectively. The obtained In:GaN/Ta3N5/Mg:GaN heterojunction photoanode shows enhanced bulk carrier separation capability and better injection efficiency at photoanode/electrolyte interface, which lead to a record-high applied bias photon-to-current efficiency of 3.46% for Ta3N5-based photoanode. Furthermore, the roles of the In:GaN and Mg:GaN layers are distinguished through mechanistic studies. While the In:GaN layer contributes mainly to the enhanced bulk charge separation efficiency, the Mg:GaN layer improves the surface charge inject efficiency. This work demonstrates the crucial role of proper interface engineering for thin film-based photoanode in achieving efficient PEC water splitting. Solar-to-fuel energy conversion requires well-designed materials properties to ensure favorable charge carrier movement. Here, authors employ interface engineering of Ta3N5 thin film to enhance bulk carrier separation and interface carrier injection to improve the water-splitting efficiency.

Araki T., Gomez-Solano J.R., Maciołek A.

We study the relaxation dynamics of a binary liquid mixture near a light-absorbing Janus particle after switching on and off illumination using experiments and theoretical models. The dynamics is controlled by the temperature gradient formed around the heated particle. Our results show that the relaxation is asymmetric: The approach to a nonequilibrium steady state is much slower than the return to thermal equilibrium. Approaching a nonequilibrium steady state after a sudden temperature change is a two-step process that overshoots the response of spatial variance of the concentration field. The initial growth of concentration fluctuations after switching on illumination follows a power law in agreement with the hydrodynamic and purely diffusive model. The energy outflow from the system after switching off illumination is well described by a stretched exponential function of time with characteristic time proportional to the ratio of the energy stored in the steady state to the total energy flux in this state.