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.

In this work, the mechanisms for creating a combined electronic–radiative local state beneath the conduction band, consisting of intrinsic and activator electron–hole states, are experimentally substantiated. In the first part of this work, the mechanisms of the formation of intrinsic and activator electron–hole trapping centers are experimentally demonstrated in all four matrices with activators. Intrinsic electronic states are localized on activators and anions of the matrix, forming intrinsic and activator electronic states. The hole component of the electron–hole pairs is localized near the activators. Thus, the energy of intrinsic electronic excitations localized in the matrix in the form of combined electronic–radiative states is observed at 3.06–3.1 eV and 2.92–2.95 eV. Radiative states are excited by photon energies of ~4.5 eV and ~4.0 eV, resulting in recombination emissions at 3.06–3.1 eV and 2.92–2.95 eV, as well as activator emissions at 2.06 eV for ${Mn}^{2+}$, 2.5 eV for ${Tb}^{3+}$, and 2.56 eV and 2.16 eV for ${Dy}^{3+}$. Energy transfer from the matrix to emitters or activators occurs during the decay of the combined radiative state. Upon heating, electrons localized on anions and activators delocalize at temperatures of 200–350 K. The energy released during the recombination of an electron with a hole near the activators is transferred to the activators. This process facilitates energy transfer to activators in dosimeters and detectors.

In YPO₄:Bi irradiated with photons in the energy range of 5.5–6.2 eV and with X-rays, sensitization-related luminescent states are formed in the 4.43–3.35 eV energy range, appearing as a broad emission band. The excitation spectrum of this broad band lies in the photon-energy range of 5.9–6.2 eV. As in many phosphor materials, these sensitization-related luminescent states are formed as a result of charge transfer from an excited host anion to neighboring ions and impurity centers introduced into the lattice, leading to the formation of electron-trapping centers. Upon excitation of irradiated YPO₄:Bi with photons in the energy range of 4.43–3.35 eV, two groups of emission bands are observed: at 3.1–2.9 eV and at 2.8–2.25 eV. These emissions are excited within two spectral regions, from 4.43 to 3.8 eV and from 3.7 to 3.25 eV, and appear as several recombination-related bands. Reflectance spectrum measurements show that, within the transparency region of the host matrix, additional energy levels appear in the 4.43–3.35 eV spectral range. Excitation through these levels gives rise to the observed recombination luminescence, and their energy positions correspond to the excitation spectra of the respective recombination emission bands.