A series of fluorophosphate glasses with CdSe and CdSe+ZnSe are successfully synthesized. After heat treatment above the glass transition temperature, CdSe quantum dots with sizes 1.5-5.5 nm are formed. The luminescence spectra of CdSe quantum dots are analyzed at various temperatures, excitation energies and chemical composition of glass. The influence of selenium content on the growth features of quantum dots is shown. The size dependence of luminescence quantum yield on the QDs size is found. The 2.0-2.5 nm-sized QDs demonstrate trap emission in the region of 1.7-1.85 eV with a maximum quantum yield of 60 %. It is found that only a broad band due to the transition from the low state of the conduction band and the shallow donor trap states to the deep accepter trap levels is observed. This broad emission band is observed at any selenium cadmium ratio and zinc introduction.

The photoluminescence (PL) spectra of CsPbBr3 perovskite nanocrystals grown in a fluorophosphate glass matrix exhibit phonon replicas of the exciton line. The dependence of intensity of the phonon replica on its number is simulated taking into account the difference in the curvature of the excited and ground adiabatic potentials. The Raman spectra of CsPbBr3 nanocrystals are measured. Calculations based on the density functional theory is performed to obtain the spectrum of phonon states of these crystals in the orthorhombic phase. The phonon frequencies observed in the PL and Raman spectra are compared with the calculation results.

Lead halide perovskite nanocrystals (NCs) in a glass matrix combine excellent optical properties and stability against environment. The spectral and temporal characteristics of photoluminescence from CsPbBr3 and CsPb(Cl,Br)3 nanocrystals in a fluorophosphate glass matrix are measured in a temperature range from 6 to 270 K in order to reveal factors that determine their quantum yield and recombination dynamics. At low temperatures, the recombination dynamics is characterized by three decay components with timescales on the order of 1 ns, 10 ns, and 1 mu s. The relative contributions of the corresponding processes and their characteristic times are strongly temperature dependent. The emission intensity decreases with growing temperature. This effect is stronger in smaller NCs, which highlights the role of surface states. These experimental results are discussed on the basis of a model taking into account the NC energy structure and the presence of electron and hole surface trap states. The photoluminescence dynamics at low temperatures is dominated by charge-carrier radiative recombination and relaxation to shallow traps. At temperatures exceeding 100 K, the dynamics is affected by carrier activation to the excited states.

The photoluminescence (PL) spectra of CsPbBr3 perovskite nanocrystals grown in a fluorophosphate glass matrix exhibit phonon replicas of the exciton line. The dependence of intensity of the phonon sidebands are simulated taking into account the difference in the curvature of the excited and ground adiabatic potentials. The Raman spectra of CsPbBr3 nanocrystals are measured. Calculations based on the density functional theory is performed to obtain the spectrum of phonon states of these crystals in the orthorhombic phase. The phonon frequencies observed in the PL and Raman spectra are compared with the calculation results.

Received 10 March 2023DOI:https://doi.org/10.1103/PhysRevB.107.119902©2023 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasExciton polaritonExcitonsPhysical SystemsQuantum wellsTechniquesLiquid helium coolingLuttinger–Kohn modelMolecular beam epitaxyReflectivityCondensed Matter, Materials & Applied Physics

Light-hole (lh) excitons (Xlhs) in quantum wells (QWs) are hardly studied compared with heavy-hole (hh) excitons (Xhhs), mainly due to the difficulties of their experimental observation. In this paper, a comprehensive study of both types of excitons in high-quality GaAs/AlGaAs QWs of different widths is performed. We focus on the energy positions of exciton resonances and the exciton-light interaction. The effect of mixing lhs and hhs in GaAs-based structures on these exciton characteristics is investigated. The corrections to the exciton energy due to mixing are only a fraction of millielectronvolts for wide QWs, in which the energy levels of Xhhs and Xlhs are close to each other. It is also experimentally found that the oscillator strength of Xlhs is similar to 2.5 times less than that of Xhhs. This value noticeably deviates from the 3:1 oscillator strength ratio known for optical transitions between free electron and hole states. This deviation originates from the different squeezing of the Xlh and Xhh wave functions due to distinct values of the effective masses of the Xlh and Xhh in the heterostructure. Mixing of hh and lh valence bands is not so important.

The anti-Stokes luminescence of perovskite CsPbBr3 nanocrystals in a fluorophosphate glass matrix has been detected and experimentally studied upon optical excitation to the low-energy edge of the photoluminescence band. The intensity of anti-Stokes luminescence depends linearly on the pump power and increases rapidly with increasing temperature. A simple three-level model is proposed. It well describes the main regularities of the observed phenomenon.

The anti-Stokes photoluminescence (PL) of perovskite CsPbBr3 nanocrystals in a fluorophosphate glass matrix has been found and experimentally studied upon optical excitation to the low-energy edge of the photoluminescence band. The intensity of anti-Stokes PL depends linearly on the pumping power and increases rapidly with increasing temperature. A simple three-level model is proposed that describes well the main regularities of the observed phenomenon. Keywords: perovskites, nanocrystals, anti-Stokes photoluminescence, CsPbBr3, fluorophosphate glass.

The name of the fifth author should read Mohrain.

AbstractReflectance and photoluminescence spectra of the ZnO/Zn_0.78Mg_0.22O structures with ZnO quantum wells and thick ZnO and Zn_0.78Mg_0.22O layers have been thoroughly investigated at different temperatures and excitation intensities and wavelengths. All the observed spectral lines have been identified. It has been established that the built-in electric field does not affect the spectrum as strongly as was expected. The built-in field is apparently effectively screened by the carriers that have migrated to the bands from donor and acceptor levels. The parameters determining the exciton properties in zinc oxide have been estimated.

Reflectance and photoluminescence spectra of the ZnO/Zn 0.78 Mg 0.22 O structures with ZnO quantum wells and thick ZnO and Zn 0.78 Mg 0.22 O layers have been thoroughly investigated at different temperatures and excitation intensities and wavelengths. All the observed spectral lines have been identified. It has been established that the built-in electric field does not affect the spectrum as strongly as was expected. The built-in field is apparently effectively screened by the carriers that have migrated to the bands from donor and acceptor levels. The parameters determining the exciton properties in zinc oxide have been estimated.