Photoluminescence Research Articles

Insight into unusual complex thermodynamical behaviour of citric acid and ethanolamine solution

Inverse freezing fluids (IFF) are the new field of science that thermodynamically acts opposite to conventional fluids. These IFFs are novel artificial materials that work as typical thermal metamaterials. This paper reports the IFF phenomenon with basic chemicals such as citric acid and ethanolamine subjected to different conditions. The amine molecule within the precursor compound is crucial in attaining this phenomenon. Its respective inter and intramolecular ‘hydrogen’ atoms remain the key reason for this effect. Results of rheometry, Raman, proton nuclear magnetic resonance (1HNMR), photoluminescence (PL) spectroscopy, and thermogravimetric analysis (TGA) of this fluid confirmed this phenomena, collectively. Experimental findings confirm the reversible phase transformation which is contrary to the conventional fluids. It will open the interest in finding new thermal metamaterials. This study can be considered the first attempt at synthesizing IFFs through a new preparation method and analysed in detail. Many challenges were faced during synthesis and characterizations, so this study will help to resolve the complexity in this domain. Further, the sample was sintered and found to be multi-layered reduced graphene oxide (rGO) powder. This rGO sample’s structural, chemical nature, and morphology are studied through x-ray diffraction (XRD), Fourier transformed infra-red (FTIR), Raman spectroscopy, scanning electron microscope (SEM), transmission electron microscope imaging and energy dispersive analysis of x-rays (EDAX). XRD pattern confirmed the presence of the main peak at 26° (2θ) corresponding to the basal reflection (002) of rGO phase. It was further evidenced by its D and G bands of Raman spectra at 1357 and 1574 cm−1, respectively. FTIR analysis also revealed a reduced OH- band whereas EDAX analysis confirms the purity of rGO by the presence of carbon and oxygen peaks only. Multilayer formation of rGO was confirmed by SEM and TEM observations and found that the measured thickness of the sheet was nearly 1 nm.Graphical

Triangular-shaped Cu-Zn-In-Se-based nanocrystals with narrow near infrared photoluminescence.

Tunable optical properties exhibited by semiconductor nanocrystals (NCs) in the near infrared (NIR) spectral region are of particular interest in various applications, such as telecommunications, bioimaging, photodetection, photovoltaics, etc. While lead and mercury chalcogenide NCs do exhibit exemplary optical properties in the NIR, Cu-In-Se (CISe)-based NCs are a suitable environment-friendly alternative to these toxic materials. Several reports of NIR-emitting (quasi)spherical CISe NCs have been published, but their more complex-shaped counterparts remain rather less explored. The emerging anisotropic nanomaterials have gained significant interest owing to their unique optical properties arising due to their specific shape. While several examples of non-spherical Cu-In-S-based NCs have been reported, examples of CISe-based anisotropic NCs are rather scarce, and those with intensive photoluminescence (PL) are not yet developed. In this work, we present a one-pot approach to synthesize quaternary Cu-Zn-In-Se (CZISe) triangular NCs with intensive PL in the NIR region. The NCs synthesized exhibit tetragonal crystal structure and, depending on the reaction conditions, are single triangular particles or stacks of triangular blocks of varied lateral sizes but rather uniform thickness. The synthesis involves the formation of In2Se3 seeds with subsequent incorporation of copper and growth of triangular CISe NCs, followed by the incorporation of zinc and the growth of a ZnS shell. Importantly, the PL band widths of the final core/shell heterostructured NCs are narrow, down to 102 meV, which is a rarely observed characteristic for this class of materials and can be attributed to their anisotropic shape and the absence of thickness and compositional inhomogeneities of their building blocks. The PL of the CZISe/ZnS NCs can be tuned in the range of 1082-1218 nm reaching a quantum yield of up to 40% by varying their size and composition. To the best of our knowledge, this is the farthest and the narrowest PL achieved for CISe-based NCs so far, which widens application perspectives of this material in NIR LEDs, bioimaging, and photovoltaics.

Broad-Temperature Optical Thermometry via Dual Sensitivity of Self-Trapped Excitons Lifetime and Higher-Order Phonon Anharmonicity in Lead-Free Perovskites.

Broad-temperature optical thermometry necessitates materials with exceptional sensitivity and stability across varied thermal conditions, presenting challenges for conventional systems. Here, we report a lead-free, vacancy-ordered perovskite Cs2TeCl6, that achieves precise temperature sensing through a novel combination of self-trapped excitons (STEs) photoluminescence (PL) lifetime modulation and unprecedented fifth-order phonon anharmonicity. The STEs PL lifetime demonstrates a highly temperature-sensitive response from 200 to 300 K, ideal for low-to-intermediate thermal sensing. In contrast, the Eg phonon mode undergoes significant linewidth broadening due to five-phonon scattering processes, with a distinct nonlinear temperature dependence up to 500 K. This fifth-order anharmonic effect enhances Raman-based temperature sensitivity, yielding a specific sensitivity (Sr) of 0.577% K-1 at 330 K and remaining above 0.5% K-1 at elevated temperatures. This study presents the first evidence of fifth-order anharmonic effects enhancing Raman-based temperature sensitivity, establishing Cs2TeCl6 as a versatile candidate for broad-temperature optical thermometry and opening new avenues for precise non-contact temperature sensing in advanced technological applications.

Synergistic Control of Ferroelectric and Optical Properties in Molecular Ferroelectric for Multiplexing Nonvolatile Memory.

Utilizing the correlation among diverse physical properties to facilitate multiplexing and multistate memory is anticipated to emerge as an efficient strategy to enhance memory capacity, achieve device miniaturization, and ensure information security. As an important functional material, ferroelectrics have long been considered as a potential candidate in multistate memory devices. Furthermore, the integration of optical response offers an alternative path to realizing multiplexing features, further enhancing the versatility and efficiency of these devices. However, combining ferroelectricity and optical activity is always challenging because ferroelectricity is very sensitive to the crystal structure. In this study, on the correlation between ferroelectric polarization (FP) and optical properties in molecular ferroelectric material, trimethylchloromethyl ammonium trichloromanganese (TMCM-MnCl3) is reported. This research demonstrated that the FP can modulate the photoluminescence (PL) emission, while optical illumination can trigger FP reversal. Based on these, both electric-writing optical-reading (EWOR) and optical-writing electrical-reading (OWER) modes have been conclusively established, and the seamless transition between these two modes can be achieved by adjusting the excitation light intensity. These findings reveal an intriguing physical interconnection and imply the viability of implementing multiplexing and multistate memory functionalities in systems based on ferroelectrics.

Protein-templated metal nanoclusters for chemical sensing

Metal nanoclusters (MNCs) possess unique optical properties, discrete energy levels, biocompatibility and photostability, making them pivotal photoluminescent probes in chemical sensing. While substantial work has addressed the synthesis, theoretical studies and applications of gold-, copper-, and silver-based MNCs, this review introduces fresh perspectives on how the nature and concentration of templates—particularly protein molecules—affect the optical properties, stability and sensing capabilities of MNCs. We delve into the merits of using protein templates for creating highly stable MNCs with tunable photoluminescence (PL), providing a detailed comparison with non-protein based systems. This review also unveils recent advancements in the photophysical characteristics and chemical sensing applications of protein-templated MNCs, setting it apart from previous reviews by focusing on cutting-edge innovations in template influence. Challenges and future prospects for protein-templated MNCs in chemical sensing are highlighted, marking critical pathways for upcoming research. This work not only integrates current knowledge but also identifies gaps and opportunities not covered extensively in earlier reviews, such as the nuanced effects of template variation on MNCs’ functional properties.

Spectroscopic Ellipsometry and Correlated Studies of AlGaN-GaN HEMTs Prepared by MOCVD

A series of AlGaN/GaN high-electron-mobility transistor (HEMT) structures, with an AlN thin buffer, GaN thick layer and Al0.25Ga0.75N layer (13–104 nm thick), is prepared by metal–organic chemical vapor deposition and investigated via multiple techniques. Spectroscopic ellipsometry (SE) and temperature-dependent measurements and penetrative analyses have achieved significant understanding of these HEMT structures. Bandgaps of AlGaN and GaN are acquired via SE-deduced relationships of refraction index n and extinguish coefficient k vs. wavelength λ in a simple but straightforward way. The optical constants of n and k, and the energy gap Eg of AlGaN layers, are found slightly altered with the variation in AlGaN layer thickness. The Urbach energy EU at the AlGaN and GaN layers are deduced. High-resolution X-ray diffraction and calculations determined the extremely low screw dislocation density of 1.6 × 108 cm−2. The top AlGaN layer exhibits a tensile stress influenced by the under beneath GaN and its crystalline quality is improved with the increase in thickness. Comparative photoluminescence (PL) experiments using 266 nm and 325 nm two excitations reveal and confirm the 2DEG within the AlGaN-GaN HEMT structures. DUV (266 nm) excitation Raman scattering and calculations acquired carrier concentrations in compatible AlGaN and GaN layers.

Blue photoluminescence from active carboxyl adatoms on nanoporous anodic alumina films

Nanoporous anodic alumina (nPAA) films formed on aluminum in lower aliphatic carboxylic acids exhibit blue self-coloring and characteristic properties such as photoluminescence (PL), electroluminescence, and electron spin resonance. The blue colors are seemingly originated from the adsorbed radicals incorporating into the oxide during the aluminum anodization. However, there is lack of reports revealing the detailed activation mechanism of the adatoms in the complexes. This study investigates the blue PL and its correlation with the atomic and electronic structures of the active aluminum surface using multiple theoretical and experimental methods. The results show that the concentration of carboxylates at the nPAA surface is highly correlated with the blue colorization and manifest that unpaired electrons in carbon (derived from the carboxylates) bridging two aluminum atoms at surface can play as an active source of the blue colorization. Therefore, it is suggested that controlling the adsorption of the carboxylate on the alumina membrane having large surface-to-volume ratio can be an efficient way to generate the blue light for the optoelectronic applications.

Time-Dependent Growth of ZnO Nanowires: Unveiling Antibacterial and Photocatalytic Properties.

This study investigates the synthesis, characterization, and functional properties of well-aligned zinc oxide (ZnO) nanowires (NWs) obtained by a two-step hydrothermal method. ZnO NWs were grown on silicon substrates precoated with a ZnO seed layer. The growth process was conducted at 90 °C for different durations (2, 3, and 4 h) to examine the time-dependent evolution of the nanowire properties. A comprehensive characterization of the ZnO NWs was performed using several analytical techniques. Scanning electron microscopy (SEM) revealed the morphological progression, specifically tracking changes in length and diameter as a function of the growth time. Ultraviolet (UV)-visible spectroscopy was employed to determine the optical band gap, while photoluminescence (PL) analysis provided insight into the concentration of structural defects and its evolution as a function of nanowire growth. The photocatalytic efficiency of the ZnO NWs was evaluated through the degradation of the organic dye methylene blue (MB) under UV light irradiation (365 nm). The kinetic of MB degradation was monitored for each growth time, with non-purgeable organic carbon (NPOC) analysis providing a detailed perspective on the photocatalytic activity over time. The antibacterial properties were tested against Pseudomonas putida, a Gram-negative bacterium, to determine the efficiency of the synthesized ZnO NWs as antimicrobial agents. The release of zinc ions (Zn2+), a key factor in the antibacterial mechanism, was quantified using inductively coupled plasma (ICP) analysis for each sample. By exploration of the relationship between the growth time, nanostructure morphology, and functional properties, this study provides insights into optimizing the synthesis of ZnO NWs for enhanced photocatalytic and antibacterial applications. These findings contribute to the development of advanced materials for environmental and biomedical applications.

Enhanced Spontaneous Emission Rate and Luminescence Intensity of CsPbBr3 Quantum Dots Using a High-Q Microdisk Cavity.

Perovskite quantum dots (QDs) are high-efficiency optoelectronic materials attracting great interest, but further improvement in the luminescence efficiency is crucial for their application. In this work, we enhance both the spontaneous emission rate and the photoluminescence (PL) intensity of CsPbBr3 QDs by coupling them to a high quality (Q) factor SiO2 microdisk cavity. Compared to conventional metal plasmonic cavities, the dielectric cavity structure suppresses the effects of quenching and energy transfer, which could introduce complex fluctuations and nonradiative decays. As such, we obtain a 5.9-fold enhancement of the PL intensity and a 5.6-fold enhancement of the emission rate. Moreover, the different enhancement behaviors for phonon sidebands allow us to further explore the different components in the broad emission peak of ensembled QDs. These results demonstrate the great potential of microdisk cavities in enhancing the luminescence in optoelectronic devices and exploring the exciton-photophysics of perovskite QDs.

Tunable photoluminescence and energy transfer in Dy3+ and Eu3+ co-doped NaCaGd(WO4)3 phosphors for pc-WLED applications.

Elevated temperatures can lead to reabsorption and color drift, compromising the quality of phosphor-converted white light-emitting diode (pc-WLED) devices. To ensure the performance of WLEDs under these conditions, it is essential to develop luminescent materials that maintain stable color. Consequently, there is a pressing need for single-phase white-emitting phosphors with robust chromatic stability. In this work, we synthesize a series of color-tunable NaCaGd(WO4)3 (NCGW) phosphors using conventional solid-state reaction method, co-doping with Dy3+ and Eu3+ in varying ratios. X-ray diffraction, Rietveld refinement and scanning electron microscopy analyses are carried out to identify the phase purity and morphology. The photoluminescence (PL) properties are investigated under excitations of 352 nm and 393 nm. The PL emission spectra and fluorescence decay curves reveal efficient energy transfer between the Dy3+ and Eu3+ ions within the NCGW host, demonstrating tunable PL emission properties through manipulation of this energy transfer. At elevated temperatures of up to 200 °C, the positions of the characteristic emission peaks of Dy3+ and Eu3+ in NCGW phosphors remain essentially unchanged. Although the emission band intensities decrease due to thermal quenching, they retain a significant portion of their initial intensity compared to room temperature levels. For proof-of-concept studies, a single-phase NCGW:0.05%Dy3+-0.05%Eu3+ phosphor is combined with a commercial 365 nm UV chip to create a WLED device prototype. This prototype achieves a color rendering index of 81.7, a correlated color temperature of 4862 K and Commission International de I'Eclairage chromaticity coordinates of (0.35, 0.37), exhibiting comparable or superior colorimetric values to those reported in previous research. The results indicate that Dy3+ and Eu3+ co-doped NCGW phosphors, with their high chromaticity stability, have significant potential for full-spectrum WLED applications.

Structural and Optical Properties of Hydrothermally Synthesized Co0.3Zn0.7AlxFe2−𝑥O4 (x = 0.2 – 0.8) Nanoparticles

Objectives: Investigations on structural and optical studies of Co0.3Zn0.7AlxFe2-xO4 (x = 0.2 – 0.8)/CZAFO nanoparticles synthesized through hydrothermal method are presented in this paper. Methods: Co0.3Zn0.7AlxFe2-xO4 (x = 0.2 – 0.8) samples are synthesized by hydrothermal method. Structural and Optical characterization of the samples is done by using X-ray diffraction (XRD), photoluminescence (PL), UV-Vis spectrophotometer and Fourier transform infrared spectroscopy (FTIR). Findings: The spinel cubic structure is established with the X-Ray Diffraction pattern. The crystallite size values range from 5.610 to 6.188 nm increasing with substitution Al3+ concentration x, according to the Debye-Scherer formula. Photoluminescence emission between 360 nm and 615 nm exposes the radiative deficiencies and oxygen vacancies by the effect of Al3+ substituting CZFO nanoparticles at room temperature. FT-IR confirms the existence of metal oxides. Using the UV-visible spectrophotometer and the impact of Al3+ substitutions on Co-Zn ferrite nanoparticles, optical energy band gap in the samples was investigated. Samples' energy band gap decreases as the Al3+ content rises, from x = 0.2 to 0.8. Novelty: Investigations on the effect of Al substitution on structural and Optical properties of Co0.3Zn0.7AlxFe2-xO4 nanoparticles were optical band gap energies ranging from 1.647 eV to 1.487 eV, depending on the composition (x = 0.2, 0.4, 0.6, and 0.8), hold promise for sort of optoelectronic applications and including photocatalysis, optical sensors and biomedical imaging. Also, optical band gap energy (Eg) values were provided to indicate the semiconductor nature of CZAFO nanoparticles. Keywords: Aluminum, Nanoparticles, Hydrothermal Method, Optical Property, Cobalt-Zinc ferrite (CZFO)

A Study of Halide Ion Exchange-Induced Phase Transition in CsPbBr3 Perovskite Quantum Dots for Detecting Chlorinated Volatile Compounds.

The unique optical properties of perovskite quantum dots (PQDs), particularly the tunable photoluminescence (PL) across the visible spectrum, make them a promising tool for chlorinated detection. However, the correlation between the fluorescence emission shift behavior and the interface of phase transformation in PQDs has not been thoroughly explored. In this study, we synthesized CsPbBr3 PQDs via the hot-injection method and demonstrated their ability to detect chlorinated volatile compounds such as HCl and NaOCl through a halide exchange process between the PQDs' solid thin film and the chlorinated vapor phase. This exchange process, which occurs alongside chloride (Cl) and bromine (Br) ion exchange and halide atom rearrangement, leads to sequential structural changes: the initial CsPbBr3 cubic Pm3̅m phase transitions to the CsPb2BrxCl5-x tetragonal I4/mcm phase, which subsequently transforms into the CsPbBrxCl3-x orthorhombic Pnma phase. The detailed exploration of this proposed mechanism during chlorinated vapor detection with CsPbBr3 PQDs thin films, supported by X-ray diffraction (XRD) analysis and PL spectrum over time, revealed high sensitivity to HCl vapor. The limit of detection (LOD) for HCl vapor was determined to be 0.02 ppm in visual recognition and 0.005 ppm via PL spectra. Additionally, the LOD for NaOCl was established at 0.50 ppm, facilitated by the photolysis reaction accelerating the conversion of NaOCl to HCl vapor under UV light irradiation. These insights have enriched our understanding of the mechanisms involved and broadened the potential use of CsPbBr3 PQDs as PL detection probes for chloride ions.

Mosaic Structure of GaN Film Grown on Sapphire Substrate by AP-MOCVD: Impact of Thermal Annealing on the Tilt and Twist Angles

A GaN layer with a thickness of 2 µm was grown on a sapphire substrate using atmospheric pressure metal–organic chemical vapor deposition (AP-MOCVD). Subsequently, the layer was annealed under a nitrogen atmosphere at temperatures ranging from 1000 °C to 1120 °C. High-resolution X-ray diffraction (HRXRD) analysis reveals the impact of thermal annealing on the mosaic structure of the GaN, specifically the tilt and twist variations in four planes: (00.2), (10.3), (10.2), and (10.1). Interestingly, the observed trends suggest a differential effect of annealing on screw and edge dislocation densities. The annealing process reduces the edge and screw dislocation density. Lower values (Dscrew = 1.2 × 108 cm−2; Dedge = 1.6 × 109 cm−2) were obtained for the sample annealed at 1050 °C. Notably, both tilt and twist angles exhibited a minimum at 1050 °C (tilt = 252 arcsecs, and twist = 558 arcsecs), indicating improved crystal quality at this specific temperature. Photoluminescence (PL) spectroscopy further complemented the structural analysis. The intensity and broadening of the yellow band (YL) in the PL spectra progressively increased with the increasing annealing temperature, suggesting the presence of additional defect states. The near band edge PL emission (3.35 and 3.41 eV) variation upon thermal annealing was correlated with the mosaic structure evolution.

New highly efficient phosphorescent manganese halides as green and blue emitters.

Three new manganese compounds on 5-(pyridin-2-yl)-3-phenyl-1,2,4-triazole (L) basis (HL)4[MnBr4]2·H2O (1), (HL)2[MnCl4] (2) and [MnL2Cl2]·H2O (3) have been synthesized and characterized in terms of their structure, photoluminescence (PL), and electroluminescence (EL) properties. Compounds 1 and 2 exhibit bright green luminescence (λem ≈ 550 nm) with high quantum yields of 75.1 and 71.2%, and 3 emits unusual blue emission at 438 nm with a quantum yield of 43.9%. Analysis of the spectral properties of complexes 1 and 2 indicates that luminescence is determined by the transfer of excitation energy from the triazole cation to the manganese cation. Electroluminescent devices based on complexes 1 and 3 show high brightness values of 3033 and 5230 Cd m-2, respectively.

Characterization of Cs2AgInCl6: Bridging Optical and Electrical Properties for Advanced Optoelectronic Applications

ABSTRACTLead‐free double perovskites, such as Cs2AgInCl6, represent a promising class of materials for optoelectronic applications due to their favorable properties and environmental sustainability. This work focuses on the synthesis and comprehensive characterization of Cs2AgInCl6, employing a range of techniques including X‐ray diffraction (XRD) for structural verification, thermogravimetric analysis (TGA) to assess thermal stability, and UV–visible absorption measurements to determine the optical bandgap energy of 3.32 eV. Additionally, we explore photoluminescence (PL) and decay measurements to elucidate the luminescent properties of the compound. Complex impedance measurements are performed under both blue and red light to investigate the electrical behavior, revealing two distinct conduction mechanisms: the overlapping large–polaron tunneling (OLPT) and nonoverlapping small–polaron tunneling (NSPT). We analyze the implications of our findings on the current–voltage (I–V) behavior and trap density, further supported by Raman spectroscopy under both illumination conditions. The combined insights from optical and electrical characterizations highlight the potential of Cs2AgInCl6 in optical applications, paving the way for its use in advanced optoelectronic devices.

Electrical Control of Photoluminescence in 2D Semiconductors Coupled to Plasmonic Lattices.

Integrating two-dimensional (2D) semiconductors into nanophotonic structures provides a versatile platform for advanced optoelectronic devices. A key challenge in realizing these systems is to achieve control over light emission from these materials. In this work, we demonstrate the modulation of photoluminescence (PL) in transition metal dichalcogenides (TMDs) coupled to surface lattice resonances in metal nanoparticle arrays. We show that both the intensity and the emission angle of light can be tuned by adjusting the lattice parameters. By applying gate electrodes to electrostatically dope the TMDs coupled to plasmonic lattices, we achieve PL intensity switching over 2 orders of magnitude with a low applied voltage. Our results represent an important step toward electrically powered and electrically tunable light sources based on 2D semiconductors.

Delayed Fluorescence in Dual-Doped Perovskite Nanocrystals: Insight into the Role of Dopants.

This study investigates the photophysical behaviour of Mn/Fe and Mn/Sn co-doped CsPbCl3 perovskite nanocrystals (NCs) to explore carrier dynamics and dopant interactions. Using gated photoluminescence (PL) and temperature-dependent measurements, we elucidate the impact of dopant chemistry on exciton behaviour, focusing on vibrationally assisted delayed fluorescence (VADF) and energy transfer mechanisms. The efficiency of VADF is influenced by factors such as the bandgap, temperature, quantum confinement, and host composition. In Mn/Fe co-doped NCs, Fe-induced trap states introduce additional radiative pathways, resulting in a unique emission around 515 nm. In contrast, in Mn/Sn co-doped NCs, Sn captures photoexcited carriers, preventing the VADF process and leading to non-radiative decay. The findings provide key insights into dopant-dopant interactions and the mechanisms governing carrier transfer, enhancing our understanding of these materials for future optoelectronic applications.

Bandgap Engineering Based on A-site Ions Tuning in Tin Halide Perovskite.

Tin-based halide perovskites (ASnX3) have garnered substantial interest due to their unique photoelectric properties and environmentally friendly features. The A-site ions tuning strategy has been proven to promote material performance. However, there is a lack of systematic research on the optical properties, lattice structure variation, and band structure evolution in tin-based perovskites when the A-site ions tune from organic to inorganic. Herein, MA1-xCsxSnBr3 and MA1-xCsxSnI3 (0≤x≤1) flakes are synthesized through a one-pot reaction method. By controlling the Cs ratio, a tunable photoluminescence (PL) emission covering a wide range of 560-685 nm can be observed in MA1-xCsxSnBr3, with bandgap tuned from 1.8 to 2.15 eV, while the PL ranges from 900 to 950 nm with the bandgap 1.2-1.3 eV for MA1-xCsxSnI3. Besides, the PL intensity of MA1-xCsxSnBr3 significantly enhances with the increasing Cs ratio. First-principles calculations reveal that the octahedron shrinks gradually as the Cs ratio increases. It increases the orbital overlap between Sn and Br and causes a symmetry variation, thus decreasing the bandgap and increasing emission intensity. This work reveals the photophysical mechanism of improved optical properties and bandgap variation in tin-based perovskites, paving the way for their future applications.

Modification of Gallium Nitride Defect Structure by Microwave Radiation Treatment

GaN has incredible potential for applications in high‐electron‐mobility transistors, ultraviolet light‐emitting diodes, and gas sensor systems. Herein, the results of the study of modification of the structure of GaN films formed on sapphire substrates by microwave radiation treatment (MRT) are presented. In particular, the influence of the MRT (2.45 GHz) on the defect concentration in this material is investigated. Moreover, features of the long‐term evolution of the defect subsystem are tracked as well. Both spectral (photoluminescence (PL)) and structural (X‐ray) methods of investigation are applied to obtain reliable results about the concentration of defects in particular dislocations. PL and X‐ray diffraction spectra are measured to achieve this goal. These measurements are repeated after several days to estimate the temporal evolution of the defect level resulted from the MRT. It is found that the concentration of screw dislocations changes nonmonotonously after the MRT, while the concentration of edge dislocations almost does not change. The obtained results advance the understanding of the processes, which may be useful for defect engineering by MRT.

Nucleation and Growth of Monodisperse and Monocrystalline Wurtzite CdSe Nanocrystals: Zinc Alkanoates as Neutral Ligands.

Here, we demonstrate that monocrystalline (free of stacking faults) wurtzite CdSe nanocrystals with monodisperse size, shape (dots, rods, or wires), and facet structure are synthesized in both strongly confined and weakly confined size regimes. Considering the unique c-axis of wurtzite CdSe, we introduce a new type of neutral ligand (e.g., zinc-alkanoate ones) to pair with their dominating nonpolar low-index facets. Nucleation of the stacking fault-free wurtzite seeds instead of zinc-blende tetrahedrons is identified as the key step, which is optimized by a set of conditions matching the neutral zinc-alkanoate ligands. In the following growth stage, conditions are much less stringent, although the neutral zinc-alkanoate ligands are still critical in achieving nearly atomically flat facets of those monocrystalline nanocrystals. In the strongly confined size regime, the ensemble photoluminescence (PL) full-width-at-half-maximum (FWHM) of wurtzite CdSe nanocrystals reaches a record low (59 meV). In the weakly confined size regime, dual-peak PL caused by thermal population is observed. Monodisperse and monocrystalline wurtzite CdSe nanocrystals show distinctively size-dependent optical properties, in comparison with their zinc-blende counterparts. Results here suggest that the atomically precise synthesis of colloidal semiconductor nanocrystals is feasible, implying an advanced class of nanomaterials for exploring various optical and optoelectronic applications.