The transmittance, reflectivity, and photoluminescence in the range 0.8–1.7 eV at 300 K and 77 K in the spectral range 0.6–6.0 eV at 300 K of thin films of CdTe synthesized on different substrates by thermal evaporation in a quasi-closed volume were studied. A strong dependence of the intensity and position of the band–band and excitonic luminescence bands on the substrate quality was discovered. The excitonic luminescence bands of films on silicon and glass were shifted by 10 meV to the short-wavelength region because of internal stresses in the films owing to the mismatch between the unit-cell parameters of the substrate and film. The transparency region of films cleaved from glass shifted to the longwavelength region because of the density tails of electronic states in the band gap caused by disordering of the films and the longer wavelength of the light than the roughness of the films on the growth and nucleation side. The best structural perfection was characteristic of films on a CdTe substrate based on the obtained dependences of the intensity and spectral position of the photoluminescence lines.

Resonances of free excitons at energies A 1.0409 eV, B 1.0445 eV, and C 1.2690 eV were detected in reflection spectra of single crystals of the direct-gap compound CuInSe2 at a temperature of 8.6 K. The appearance of the three reflection resonances A, B, and C could be explained by removal of degeneracy from valence-band energy levels due to the influence of crystal field and spin–orbit interaction on the tetragonal lattice of CuInSe2 with ΔCF 5.4 meV and ΔSO 224 meV. Measurements of the temperature dependence of the reflection spectra in the range 8.6–90 K showed the energies of free-exciton resonances A and B increased because of deformation of the unit cell (tetragonal stretching) of the CuInSe2 lattice with the chalcopyrite structure. The binding energies of free excitons A and B were determined as 10.7 and 152 meV based on temperature quenching of exciton resonances A 1.0409 eV and B 1.0445 eV

The effect of irradiation with different doses of 4-MeV electrons on radiative recombination of nonequilibrium charge carriers in Cu(In,Ga)(S,Se)2 thin films of solar cells was studied. Near-edge photoluminescence (PL) in the energy range 0.9–1.2 eV in nonirradiated and irradiated direct-gap Cu(In,Ga)(S,Se)2 solid solutions was caused by optical interband transitions and radiative recombination through energy levels of acceptor- and donor-type structure defects in the presence of strong potential fluctuations. PL spectra measured in the temperature range 5–300 K exhibited energy shifts of the near-edge PL band maxima and redistributions of their intensities in thin films after irradiation with different doses of electrons. The activation energies of nonradiative recombination were determined from the quenching of PL band intensities. The possible nature of structural defects in nonirradiated and electron-irradiated Cu(In,Ga)(S,Se)2 solid solutions was discussed.

The phase-structural composition of a silica film grown on Si substrate implanted with Zn ions at room temperature with different fluences has been studied using transmission electron microscopy and electron diffraction. The small clusters (1–2 nm) and the large clusters (5–7 nm) have been formed in as-implanted silica films with the Zn concentration of 6–7 at % and 16–18 at %, respectively. Furnace annealing at 750 °С for two hours results both in the formation of the orthorhombic Zn2SiO4 phase (space group R-3) in the case of low fluence (5 · 1016 cm–2) and in the formation of the cubic ZnO phase (space group F-43m) in the case of high fluence (1 · 1017 cm–2). It has been shown that impurity loss during implantation and subsequent annealing increase with fluence of implanted ions. The fraction of Zn atoms in clusters has been estimated to be 15 % and 18 % for fluences (5 · 1016 cm–2) and (1 · 1017 cm–2), respectively. It has been shown that residual Zn impurities dissolved in silica matrix noticeably suppress the light-emitting properties of silica with embedded Zn2SiO4 and ZnO nanocrystals.

Sol-gel technology has attracted attention in the fabrication of diverse luminescent materials and thin film structures, with forms that range from powders to microcavities. The optical properties of sol-gel-derived structures depend on the sol composition, deposition, and heat treatment conditions, as well as on the film thicknesses and other factors. Investigations on the upconversion luminescence of lanthanides in film structures and materials are also ongoing. In this study, we synthesized three different types of materials and film structures using the same sol, which corresponded to a Ba0.76Er0.04Yb0.20TiO3 xerogel, as follows: (a) the target form, which used the explosive compaction method for sol-gel-derived powder; (b) single-layer spin-on xerogel films annealed at 450 and 800 °C; and (c) microcavities with an undoped SiO2/BaTiO3 Bragg reflector surrounding a Ba0.76Er0.04Yb0.20TiO3 active layer. The BaTiO3:(Er,Yb)/SiO2 microcavity exhibited an enhancement of the upconversion luminescence when compared to the BaTiO3:(Er,Yb) double-layer film fabricated directly on a crystalline silicon substrate. The reflection spectra of the BaTiO3:(Er, Yb)/SiO2 microcavity annealed at 800 °C demonstrated a deviation of the maxima of the reflection within 15% for temperature measurements ranging from 26 to 120 °C. From the analyses of the transmission and reflection spectra, the optical band gap for the indirect optical transition in the single layer of the BaTiO3:(Er,Yb) spin-on film annealed at 450 °C was estimated to be 3.82 eV, while that for the film annealed at 800 °C was approximately 3.87 eV. The optical properties, upconversion luminescence, and potential applications of the BaTiO3:(Er,Yb) sol-gel-derived materials and structures are discussed in this paper.

Zinc selenide nanocrystals (NCs) were successfully synthesized in silicon dioxide (silica grown on a silicon wafer) by high-fluence implantation of Zn + and Se + ions with subsequent rapid thermal annealing at 1000 °C for 3 min. The high crystalline quality of the zinc blende ZnSe nanoclusters was proven by transmission electron microscopy with selected area electron diffraction and Raman spectroscopy. Low-temperature photoluminescence (PL) reveals the recombination of excitons in ZnSe, which further indicates a good crystalline quality of the synthesized nanocrystals. PL analysis shows a strong coupling of phonons and excitons. The Huang–Rhys parameter of the longitudinal optical phonon in the exciton transition S is in the range of 0.6–0.7. Despite the excellent quality of the ZnSe NCs synthesized in silica, defect states inside the NCs or at the NCs/SiO 2 interface with activation energies of 0.1–0.2, 0.45 and 0.67 eV play a crucial role in radiative recombination.

Erbium-doped barium titanate (BaTiO3:Er) xerogel film with a thickness of about 500 nm was formed on the porous strontium titanate ([Formula: see text] xerogel film on Si substrate after annealing at 800[Formula: see text]C or 900[Formula: see text]C. The elaborated structures show room temperature upconversion luminescence under 980 nm excitation with the photoluminescence (PL) bands at 523, 546, 658, 800 and 830 nm corresponding to 2[Formula: see text]4[Formula: see text], 4[Formula: see text][Formula: see text], 4[Formula: see text][Formula: see text] and 4[Formula: see text]4[Formula: see text] transitions of trivalent erbium. Raman and X-ray diffraction (XRD) analysis of BaTiO3:Er\porous SrTiO3\Si structure showed the presence of perovskite phases. Its excellent up-conversion optical performance will greatly broaden its applications in perovskite solar cells and high-end anti-counterfeiting technologies.

The SiNx/SiOx and SiOx/SiNx/SiOx structures were fabricated on silicon substrates by plasma-enhanced and low-pressure chemical vapour deposition. It was shown that upper silicon oxide layer enhances photoluminescence yield from silicon nitride layer in three times. Furthermore, top silicon oxide layer protects underlying nitride layer from un-intended oxidation during rapid thermal annealing in inert ambient (1100 ?C, 3 min). The role of silicon oxide unintentionally formed during SiNx annealing and the specially deposited top SiO2 layer on SiNx photoluminescence have been discussed.

Approaches to the formation of epitaxial structures containing two-dimensional Si and Ge layers embedded in a CaF2 dielectric matrix have been developed. Raman study demonstrates the presence of narrow peaks related to Si-Si and Ge-Ge bond vibrations in the growth plane of structure. In the photoluminescence spectra of the created structures, emission bands, which can be associated with the radiative recombination of charge carriers in two-dimensional Si and Ge layers embedded in CaF2 have been found.

In this work we have investigated the effect of thermal annealing of thin ZnO:Tb3+ films obtained by the combined method of electrochemical deposition of Tb ions onto silicon substrates and subsequent reactive magnetron sputtering of a zinc target on the substrates on the structural properties, optical and photoelectric properties. ZnO:Tb3+ films with annealing temperature up to 700 degrees C are close-packed structures without porosity, with an almost smooth surface and dense packing of crystallites. The crystallite size and film thickness increase insignificantly with increasing annealing temperature. The films under investigation exhibit strong green luminescence with three bands in the spectral region of similar to 1.9-2.6 eV, caused by intracenter 4f transitions on Tb3+ ions without changing the redistribution in the relative intensity of three bands with an increase in the annealing temperature. The study of the photoelectric properties showed that with an increase in the bias voltage, the maximum of the spectral sensitivity in absolute value increases and shifts to the short-wavelength region, while with an increase in the annealing temperature, the photosensitivity decreases, and upon annealing at 1100 degrees C it is practically absent.

Erbium upconversion (UC) photoluminescence (PL) from sol-gel derived barium titanate (BaTiO3:Er) xerogel structures fabricated on silicon, glass or fused silica substrates has been studied. Under continuous-wave excitation at 980 nm and nanosecond pulsed excitation at 980 and 1540 nm, the fabricated structures demonstrate room temperature PL with several bands at 410, 523, 546, 658, 800 and 830 nm, corresponding to the 2H9/2 → 4I15/2, 2H11/2 → 4I15/2, 4S3/2 → 4I15/2, 4F9/2→ 4I15/2 and 4I9/2→ 4I15/2 transitions of Er3+ ions. The intensity of erbium UC PL increases when an additional macroporous layer of strontium titanate is used beneath the BaTiO3 xerogel layer. It is also enhanced in BaTiO3 xerogel films codoped with erbium and ytterbium (BaTiO3:(Er,Yb)). For the latter, a redistribution of the intensity of the PL bands is observed depending on the excitation conditions. A multilayer BaTiO3:(Er,Yb)/SiO2 microcavity structure was formed on a fused silica substrate with a cavity mode in the range of 650–680 nm corresponding to one of the UC PL bands of Er3+ ions. The obtained cavity structure annealed at 450 °C provides tuning of the cavity mode by 10 nm in the temperature range from 20 °C to 130 °C. Photonic application of BaTiO3 xerogel structures doped with lanthanides is discussed.

The possibility of fabricating two-dimensional Si layers on a CaF 2 /Si(111) film by molecular beam epitaxy is studied. The growth conditions, under which the regions of two-dimensional Si layers are formed, are found. Raman spectroscopy, transmission electron microscopy, photoluminescence, and electron paramagnetic resonance (EPR) studies have shown that regions of two-dimensional Si layers are formed in epitaxial structures prepared by the deposition of one to three biatomic Si layers on the CaF 2 /Si(111) film surface at a temperature of 550°С. The Raman spectra of these structures exhibit a narrow peak at 418 cm –1 , which is due to light scattering on vibrations of Si atoms in the plane of a two-dimensional Si layer intercalated with calcium. The EPR spectra of multilayer structures with regions of two-dimensional Si layers embedded in CaF 2 demonstrate an isotropic signal with an asymmetric Dyson shape and the g -factor $$g = 1.9992$$ under illumination. Consequently, this signal can be attributed to photoinduced conduction electrons in extended two-dimensional Si islands. These results may be useful for understanding the mechanisms of the formation of two-dimensional materials on CaF 2 /Si(111) substrates.

The Stokes and anti-Stokes luminescence of erbium in sol–gel-derived barium-titanate xerogels (BaTiO 3 :Er) and BaTiO 3 /SiO 2 multilayer structures based on these xerogels formed on silicon substrates is studied. It is shown that the up-conversion of erbium in barium-titanate xerogels obtained from erbium nitrate or acetate is observed at an erbium concentration of >3 at %. The up-conversion of erbium is observed at an excitation wavelength of ~980 nm and characterized by an intense band in the 520–560 nm range, corresponding to the 2 H 11/2 → 4 I 15/2 and 4 S 3/2 → 4 I 15/2 radiative transitions of the erbium ion, as well as the bands in the regions of 650 and 850 nm associated with the 4 F 9/2 → 4 I 15/2 and 4 I 9/2 → 4 I 15/2 transitions, respectively. Based on the obtained BaTiO 3 :Er xerogels, multilayer BaTiO 3 :Er/SiO 2 /Si structures are formed on silicon substrates, providing a significant, compared to single-layer BaTiO 3 :Er/Si structures, increase in the intensity of erbium luminescence at the wavelength of the main radiative transition (1540 nm). The prospects of developing up-conversion coatings based on erbium-doped barium titanate for practical applications are discussed.

Thin films of Cu(In, Ga)Se2 on Mo/glass were irradiated by 10 MeV electrons at 77 K and examined by photoluminescence at 77 K before and after irradiation without warming the samples as well as after warming to 300 K. The photoluminescence spectra revealed a broad band constituting 3 merged peaks (P1, P2, P3) assigned to: band-to-band recombination (P1) and recombination of free electrons with holes localised at acceptors influenced by the valence band tail (P2, P3). Irradiation reduced the intensity of the peaks due to deep traps generated by electrons and anomalously reduced the degree of compensation of the material. Keywords: thin films, irradiation, photoluminescence, recombination, band-to-band.

The specific features of growth and the structural and optical properties of GaSi 2 layers formed by the successive deposition of Si and CaF 2 onto a Si(111) substrate with simultaneous irradiation with a high-energy electron beam are studied. The Raman spectra recorded for the electron-beam-irradiated regions exhibit peaks characteristic of CaSi 2 crystal layers. Studies of the surface morphology of the structures formed show that, under the conditions of synthesis chosen, the formation of CaSi 2 layers upon electron irradiation proceeds by a two-dimensional layer mechanism. The photoluminescence spectra recorded for the regions modified by the electron beam greatly differ from the spectra recorded outside these regions.

Approaches to the formation of epitaxial structures containing two-dimensional Si and Ge layers embedded in a CaF 2 dielectric matrix have been developed. Raman study demonstrates the presence of narrow peaks related to Si-Si- and Ge-Ge-bond vibrations in the growth plane of structure. In the photoluminescence spectra of the created structures, emission bands, which can be associated with the radiative recombination of charge carriers in two-dimensional Si and Ge layers embedded in CaF 2 have been found. Keywords: silicon, germanium, two dimensional, calcium fluoride, molecular beam epitaxy, electron irradiation, atomic structure, photoluminescence.

Представлены результаты исследования спектров излучения кристаллов и тонких пленок CuInSe 2 при непрерывном (2 Вт/см 2 ) и наносекундном импульсном лазерном возбуждении в диапазоне плотности мощности возбуждения ~1–100 кВт/см 2 и температурах 10–160 К. Обнаружено, что в кристаллах CuInSe 2 стимулированное излучение возникает в спектральной области 1,033 эВ с минимальным уровнем пороговой накачки 9,8 кВт/см 2 , а при уровнях накачки 36–76 кВт/см 2 наблюдается лазерное излучение. Установлено, что для тонких пленок CuInSe 2 , сформированных на стеклянных подложках с предварительно осажденным на стекло слоем молибдена (структура CuInSe 2 /Mo/стекло), характерно появление только стимулированного излучения в области энергий 1,014–1,097 эВ с минимальным уровнем пороговой накачки 30 кВт/см 2 при температуре 10 К. Обсуждаются механизмы возникновения стимулированного и лазерного излучения в соединении CuInSe 2 .

Photo- and cathodoluminescence in the visible range from erbium-doped barium titanate xerogels obtained in the form of a powder and a target pressed from it by explosive compaction are investigated. The powder and target exhibit upconversion luminescence of erbium ions excited at wavelengths in the regions 950–1000 and 1450–1550 nm that is characterized by strong bands at 650 and 520–560 nm and a weak band at ~820 nm that correspond to the 4F9/2 → 4I15/2, 2H11/2 → 4I15/2, 4S3/2 → 4I15/2, and 4I9/2 → 4I15/2 transitions of Er3+. The target also demonstrates cathodoluminescence at room temperature and liquid nitrogen temperature with the strongest bands at 650, 520, and 538 nm.

Phase composition, structural and optical characteristics of thin films of Cu(In 1–x Ga x )(S у Se 1-y ) 2 solid solutions with a chalcopyrite structure were investigated. According to the data of X-ray diffraction analysis the unit cell parameters were a ~ 5.720 A and c ~ 11.52 A, and the elemental compositions were x = Ga/(Ga+ In) ~ 0.14 and y = S/(S + Se) ~ 0.11 for Cu(In 1–x Ga x )(S у Se 1-y ) 2 thin films. Optical band gap of Cu(In 1–x Ga x )(S у Se 1-y ) 2 solid solutions was determined from the measurements of photoluminescence spectra and luminescence excitation spectra at a temperature of ~4.2 K and appeared to be equal ~ 1.122 eV. Mechanism of radiative recombination of nonequilibrium charge carriers in thin films of Cu(In 1–x Ga x )(S у Se 1-y ) 2 solid solutions is discussed.

Radiation-induced effects in Cu(In,Ga)Se2 alloy thin films after implantation with hydrogen ions with energies of 2.5, 5, and 10 keV and a dose of ~3 × 1015 cm–2 are studied. Comparative analysis of the optical characteristics of nonimplanted and hydrogen-implanted Cu(In,Ga)Se2 films is conducted on the basis of photoluminescence spectra and luminescence-excitation spectra recorded at liquid-helium temperature (~4.2 K). The band gap determined for Cu(In,Ga)Se2 alloys by mathematical processing of the luminescence-excitation spectra is ~1.171 eV. In the photoluminescence spectra of nonimplanted and hydrogen-implanted Cu(In,Ga)Se2 films, an intense band is detected, with a maximum at ~1.089 eV. The band is defined by the recombination of free electrons with holes localized in the valence-band tails. It is established that broad bands with maximums at the energies 0.92 and ~0.77 eV are defined by the radiative recombination of nonequilibrium charge carriers at deep energy levels of ion-induced acceptor defects formed in the band gap of Cu(In,Ga)Se2 alloys. The conditions for the effect of the ion passivation of dangling electron bonds at the surface and in the bulk of polycrystalline Cu(In,Ga)Se2 films and the nature of structural point defects and the mechanisms of radiative recombination are discussed.