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.

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.

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.

The aim of the study is to analyze the luminescent properties of hexagonal quantum dots and their bridged envelope compounds under constant and temporal spectral analysis conditions. The CdSe nanoparticles were obtained by the hot injection method. To increase the radiation efficiency, CdSe/CdS core-shell structures have been synthesized, ensuring the passivation of surface defects. Steady-state optical measurements have shown that the first absorption maximum is recorded at 546.48 nm (2.26 eV), while the photoluminescence peak falls to 565.89 nm (2.19 eV). The data obtained indicate the presence of a Stokes shift of approximately 70 meV with a quantum radiation power of 21.4%. The time-resolved luminescence has three attenuation components with lifetimes of 7, 25 and 54 nanoseconds, which gives an average value of 26 nanoseconds. For CdSe / CdS nanoparticles, a noticeable increase in the lifetime of excited states is observed — up to 103 nanoseconds, which is probably due to the stabilizing effect of the polymer medium on the surface of the quantum dots. A long-wavelength peak at 742 nm exhibited a prolonged relaxation component of ~1.033 μs, associated with structural defects in the crystal lattice. These findings highlight the critical role of synthesis parameters and surface modifications in optimizing the luminescent properties of quantum dots for various applications

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.

Разработка подходов к управлению толщиной, структурной однородностью и химическим состоянием поверхности CdSe-нанопластин актуальна для получения материалов с заданными и воспроизводимыми спектроскопическими характеристиками. В работе проведено сравнительное исследование CdSe НПЛ, полученных методом постепенного нагревания с использованием предварительно синтезированного миристата кадмия и методом горячей инжекции селеноорганического прекурсора в реакционную среду, содержащую ацетат кадмия и олеиновую кислоту. Показано, что выбранный синтетический маршрут существенно влияет на процесс формирования, толщину и однородность нанопластин. При постепенном нагревании образованию НПЛ предшествует появление промежуточных CdSe-содержащих наночастиц, а конечный продукт представлен преимущественно НПЛ толщиной 4 ML с небольшой долей 3 ML. Метод горячей инжекции приводит к формированию более однородной популяции НПЛ толщиной 3 ML. Для обоих образцов подтверждено образование структуры, производной от кубической фазы CdSe типа цинковой обманки, при этом образец, полученный методом постепенного нагревания, характеризуется более выраженной структурной неоднородностью. Различия в толщине и однородности НПЛ проявляются в их оптических свойствах и состоянии поверхности. Анализ карбоксилатных групп и элементного состава указывает на различное локальное окружение поверхностных лигандов и вероятное присутствие остаточного кадмий-миристатного компонента в образце, синтезированном с использованием миристата кадмия. Полученные результаты показывают, что природа кадмиевого прекурсора, способ образования его карбоксилатной формы и условия введения селена совместно определяют структурные, поверхностные и спектроскопические характеристики CdSe НПЛ.