Sergey G. Dorofeev

Post-synthetic doping provides a route to modify the excited-state dynamics of semiconductor nanoplatelets without coupling dopant incorporation to their initial nucleation and growth. Here, we investigate post-synthetic Mn incorporation into preformed CdSe nanoplatelets using manganese (II) diethyldithiocarbamate followed by thermal treatment under inert conditions. Structural and compositional analyses confirm the association of Mn with the nanoplatelets while preserving their platelet-like morphology and zinc-blende CdSe structure. Under the present reaction conditions, DPE-based treatments yield substantially higher Mn incorporation than HB-based treatments, demonstrating the strong sensitivity of the incorporation process to the reaction environment. Importantly, undoped control experiments show that broad visible-to-NIR emission can also arise from pristine CdSe nanoplatelets and can be strongly enhanced by thermal treatment, demonstrating that the spectral appearance of the broad band alone is not a unique signature of Mn-related states. The decisive difference is instead found in the emission dynamics: pristine and thermally treated undoped nanoplatelets, as well as low-Mn HB samples, exhibit broad-band decay on the few-microsecond timescale, whereas the main Mn-rich DPE samples display exceptionally long-lived broadband emission extending into the hundred-microsecond regime. PLE measurements further show that the low-energy emission is populated following excitation of the CdSe host. These results identify the emission kinetics, rather than the presence of broadband photoluminescence itself, as the clearest signature of additional Mn-associated relaxation pathways and demonstrate that post-synthetic reaction conditions provide a means of accessing long-lived excited-state dynamics in CdSe nanoplatelets. A representative sample also retained a comparable PLQY after more than two years of ambient storage, supporting the long-term stability of the optical response.

CdTe colloidal nanoplatelets (NPLs) are promising two-dimensional quantum emitters, but their surface chemistry has been less studied compared to CdSe NPLs. Understanding and controlling surface properties are critical for their application. In this work, we investigate the conditions under which CdTe NPLs remain stable during post-synthetic ligand exchange in mild organic environments, which is a key step for their further use. During the initial stage of the work, the effect of the stoichiometric ratio of precursors on the optical characteristics and chemical composition of CdTe NPLs obtained at a temperature of 170 °C was analysed. The concentrations of Cd and Te varied within ±50% with respect to our standard version. The results obtained by TXRF demonstrated the formation of compositions with a moderate excess of cadmium (the Cd/Te ratio varied from 1.03 to 1.19). These conclusions are consistent with the concept of Cd-terminated surfaces stabilized by carboxylate ligands. Three standard ligand exchange strategies successfully applied to CdSe nanocrystals (carboxylate → CdCl₂, → Zn(DDTC)₂ and → hexadecanethiol) were tested on CdTe nanocrystals. Contrary to expectations, treatment of CdTe with CdCl₂ or Zn(DDTC)₂ solutions did not result in a measurable shift in exciton transitions and, moreover, caused degradation of the colloidal dispersion. Our studies have identified a range of conditions under which CdTe NPLs retain their integrity during ligand exchange. While some elements of the CdSe-developed protocols can be transferred to CdTe, their applicability is limited by a narrow processing window: beyond a certain treatment time, CdTe nanoplatelets progressively lose optical stability

BF₂-rigidified anilido-pyridines have attracted considerable interest due to their photophysical properties, whereas a comprehensive study of the electronic structure and stability of their open-shell redox states has not been performed previously. To gain deeper insight into the electronic and spectral properties of the ion-radical states, as well as spin density distribution, a new series of variously furnished BF₂-rigidified anilido-pyridines was synthesized via the modular approach and studied using a wide variety of spectral, electrochemical, and DFT methods. The discovered remarkable stability of the radical-cationic state (the ESR-estimated half-life time achieves 6 h at r.t.) opens a possibility for multiple repetitive cycling between the fluorophoric neutral state and radical-cation, which causes fluorescence quenching, thus giving rise to intrinsic electrofluorochromic properties. The BF₂-locked anilido-pyridine furnished with a nitro group exhibits redox-ambipolarity, i.e., reversible both oxidation and reduction, which is extremely rare for this type of dyes. The ESR-estimated half-life of the radical-anions is 30 h at r.t. The results of the UV-vis spectroelectrochemical study of the radical-anions were rationalized using quantum-chemical calculation of the energy and localization of the electronic transitions. Intrinsic electrofluorochromism and redox-ambipolarity are complemented by low-temperature phosphorescence (the lifetimes of the triplet state were determined), which emphasizes a diversity of properties of the novel BF₂-rigidified anilido-pyridines.

Absorption spectra are widely used in laboratory practice to measure the content of a great variety of colloidal semiconductor nanocrystals. In the case of atomically thin nanoplatelets, only CdSe has been studied enough to allow such quantification, while CdTe nanoplatelets—a promising material for photodetection—are understudied in this regard. In this work, a powerful combination of total XRF spectroscopy, absorption spectroscopy and profilometry was employed for thin films to extract the absorption coefficient values. The morphology and surface composition of nanoplatelets were studied with TEM and IR spectroscopy. The molar absorption coefficient of oleate-terminated CdTe nanoplatelets at the first optical transition was measured at about 5 × 10⁴ L·mol⁻¹·cm⁻¹ (per mole of Te), which is among the highest values for AIIBVI nanomaterials. The exchange of stabilizer with hexadecanethiol induced an approximately 5-fold decrease in the volume fraction of semiconductor material in thin films and a 5-fold decrease in absorbance. The latter effect is linked to the formation of a quasi-type II heterojunction between CdTe cores and effectively half of a monolayer shell of CdS. The density effect is explained by the diminished capacity of nanoscrolls for close packing. The combination of XRF and profilometry is proposed as a technique for fast nanomorphology evaluation.

Absorption spectra are widely used in laboratory practice to measure the content of a great vari-ety of colloidal semiconductor nanocrystals. In the case of atomically thin nanoplatelets, only CdSe has been studied enough to allow such quantification, while CdTe nanoplatelets – a prom-ising material for photodetection – are understudied in this regard. In this work, a powerful combination of total XRF spectroscopy, absorption spectroscopy and profilometry were employed for thin films to extract the absorption coefficient values. The morphology and surface composition of nanoplatelets were studied with TEM and IR spectros-copy. Molar absorption coefficient of oleate-terminated CdTe nanoplatelets at the first optical transi-tion was measured at about 5·104 M-1·cm-1 (per mole of Te), which is among the highest values for AIIBVI nanomaterials. Exchange of stabilizer to hexadecanethiol induced approximately a 5-fold decrease in the volume fraction of semiconductor material in thin films and a 5-fold decrease in absorbance. The latter effect is linked to the formation of quasi-type II heterojunction between CdTe cores and effectively a half of a monolayer shell of CdS. The density effect is explained with diminished capacity of nanoscrolls for close packing. The combination of XRF and profilometry is proposed as a technique for fast nanomorphology evaluation.

Colloidal cadmium telluride (CdTe) nanoplatelets (NPLs) are promising materials for optoelectronic applications, such as photovoltaics and light-emitting diodes, due to their unique optical and electronic properties. However, controlling their growth, thickness, and stoichiometry remains challenging. This study explores the effect of synthesis temperature on the structural, optical, and stoichiometric properties of CdTe NPLs. CdTe NPLs were synthesized at temperatures of 170 °C, 180 °C, 190 °C, and 200 °C using colloidal methods. The resulting NPLs were characterized by UV–Vis absorption spectroscopy, photoluminescence (PL) spectroscopy, transmission electron microscopy (TEM), and total reflection X-ray fluorescence (TXRF) to assess their morphology, structure, and elemental composition. The results showed that the synthesis temperature significantly affected the NPL’s morphology and stoichiometry. Optimal stoichiometry was achieved at 180 °C and 190 °C, with the crystal structure transitioning from zinc blende at lower temperatures to wurtzite at higher temperatures. Optical properties, including luminescence intensity and emission peaks, also varied with temperature. The synthesis temperature is an important parameter in controlling the structural and optical properties of CdTe NPLs. The optimal conditions for obtaining NPLs with the best characteristics were identified at 190 °C, presenting important findings for further optimization of CdTe NPL synthesis for optoelectronic applications.

Colloidal quasi-two-dimensional cadmium chalcogenide nanoplatelets have attracted considerable interest due to their narrow excitonic emission and absorption bands, making them promising candidates for advanced optical applications. In this study, the synthesis of quasi-two-dimensional CdSe NPLs with a thickness of 3.5 monolayers was investigated to understand the effects of synthesis temperature on their stoichiometry, morphology, and optical properties. The NPLs were synthesized using a colloidal method with temperatures ranging from 170 °C to 210 °C and optimized precursor ratios. Total reflection X-ray fluorescence (TXRF) analysis was employed to determine stoichiometry, while high-resolution transmission electron microscopy (HRTEM) and UV-Vis spectroscopy and photoluminescence spectroscopy were used to analyze the structural and optical characteristics. The results showed a strong correlation between increasing synthesis temperature and the enlargement of nanoscroll diameters, indicating dynamic growth. The best results in terms of uniformity, stoichiometry, and optical properties were achieved at a growth temperature of 200 °C. At this temperature, no additional optical bands associated with secondary populations or hetero-confinement were observed, indicating the high purity of the sample. Samples synthesized at lower temperatures exhibited deviations in stoichiometry and optical performance, suggesting the presence of residual organic compounds.