A. F. Zatsepin

Low-temperature photoluminescence of ion-implanted SiO 2 :Sn + films and glasses

Low-temperature photoluminescence spectroscopy with pulsed synchrotron excitation is applied to study the regularities of excitation and relaxation of both point defects and nanoparticles formed by tin implantation into SiO2 films and glasses. It has been found that tin implantation followed by air and nitrogen annealing yields the formation of α-Sn nanoclusters and nonstoichiometric SnOx nanoparticles, while a stable phase of SnO2 does not appear. Alternative channels of luminescence excitation are revealed for nanoclusters, including energy transfer from excitons and electron-hole pairs of the host SiO2 matrix.

Synchrotron-Excited Photoluminescence Spectroscopy of Silicon- and Carbon-Containing Quantum Dots in Low Dimensional SiO_{2} Matrices

A comprehensive method to study semiconductor nanoparticles in thin film SiO\(_{2}\) matrices has been developed. Selective and high-intensity synchrotron excitation allows the investigation of the nanoparticles energy structure. It is shown that the interference fringes affecting the optical excitation spectra of thin films may be neutralized by means of a special numerical technique. The spectral and kinetic properties of the Si, C, and SiC quantum dots (QD) formed by ion implantation in thin silica films were studied in details. Photoluminescence thermal quenching is shown to contain two stages and is dominated by Street law at low temperatures. Several indirect QD excitation mechanisms are realized, involving point defects, free, and self-trapped SiO\(_{2}\) matrix excitons. An exciton-assisted mechanism is dominating at helium temperatures. A resonant energy transfer mechanism taking place in the silica matrix reveals average defect-QD distance of 6–9 nm. A direct excitation channel is found only for carbon nanoclusters. An overall scheme of energy levels and optical transitions in the “matrix-cluster” system is proposed.

Interference effects in the UV(VUV)-excited luminescence spectroscopy of thin dielectric films

The problem of exciting UV and VUV light interference affecting experimental photoluminescence excitation spectra is analysed for the case of thin transparent films containing arbitrarily distributed emission centres. A numerical technique and supplied software aimed at modelling the phenomenon and correcting the distorted spectra are proposed. Successful restoration results of the experimental synchrotron data for ion-implanted silica films show that the suggested method has high potential.

Electronic structure, charge transfer, and intrinsic luminescence of gadolinium oxide nanoparticles: Experiment and theory

Abstract The cubic (c) and monoclinic (m) polymorphs of Gd2O3 were studied using the combined analysis of several materials science techniques – X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectroscopy. Density functional theory (DFT) based calculations for the samples under study were performed as well. The cubic phase of gadolinium oxide (c-Gd2O3) synthesized using a precipitation method exhibits spheroidal-like nanoclusters with well-defined edges assembled from primary nanoparticles with an average size of 50 nm, whereas the monoclinic phase of gadolinium oxide (m-Gd2O3) deposited using explosive pyrolysis has a denser structure compared with natural gadolinia. This phase also has a structure composed of three-dimensional complex agglomerates without clear-edged boundaries that are ∼21 nm in size plus a cubic phase admixture of only 2 at.% composed of primary edge-boundary nanoparticles ∼15 nm in size. These atomic features appear in the electronic structure as different defects ([Gd…O OH] and [Gd…O O]) and have dissimilar contributions to the charge-transfer processes among the appropriate electronic states with ambiguous contributions in the Gd 5р – O 2s core-like levels in the valence band structures. The origin of [Gd…O OH] defects found by XPS was well-supported by PL analysis. The electronic and atomic structures of the synthesized gadolinias calculated using DFT were compared and discussed on the basis of the well-known joint OKT–van der Laan model, and good agreement was established.

Energy conversion of X-ray, ultraviolet and infrared radiation in Gd2O3 crystals doped with Er3+ ions

Spectra of photoluminescence (PL) and X-ray excited luminescence (XRL) in region of 1.5–5.0 eV, PL excitation spectra (2.8–5.8 eV), PL decay kinetics were measured in Gd2O3 crystals doped both with Er3+ and Zn2+ ions. Synchrotron radiation (VEPP-3 storage ring, Novosibirsk, Russia) were used for XRL measurements. PL spectra were studied at room temperature and T= 88 K under excitation with energy Eexc: a) in fundamental absorption region (Eexc≥Eg); b) in intracenter excitation region (Eexc<Eg); c) in infrared region (Eexc<<Eg) with using laser 980 nm diode as exciting photons (up-conversion processes). The probability of radiative transitions from excited states of the impurity center depends on Eexc. The photoluminescence efficiency in Gd2O3 doped with both Er3+ and Zn2+ ions in the green region decreases, 4F9/2→4I15/2 transitions dominate in the red region both in XRL and PL spectra. This effect is also clearly manifested in the spectra of anti-Stokes luminescence. Energy transfer between the excited Er...

Insight into the defect–molecule interaction through the molecular-like photoluminescence of SiO2 nanoparticles

Luminescence properties due to surface defects in SiO2 are the main keystone with particles that have nanoscale dimensions, thus motivating their investigation for many emission related applications in the last few decades. A critical issue is the role played by the atmosphere that, by quenching mechanisms, weakens both the efficiency and stability of the defects. A deep knowledge of these factors is mandatory in order to properly limit any detrimental effects and, ultimately, to offer new advantageous possibilities for their exploitation. Up to now, quenching effects have been interpreted as general defect conversion processes due to the difficulty in disentangling the emission kinetics by the action of the specific quenchers. To overcome this limit, we report a time-resolved investigation of the effects induced in specific controlled molecular environments (N2, O2, CO2 and H2O) on the exceptional molecular-like luminescence that is observed around 3.0–3.4 eV in SiO2 nanoparticles. A comparison with the effects under vacuum indicates changes of the luminescence intensity and lifetime that agree with two quenching mechanisms, static and dynamic. The peculiarity of the spectral features, together with a powerful investigation approach, makes this the system of choice to probe inside the dynamics of the molecule–defect interactions and to reveal promising characteristics for molecular-sensing purposes.

Luminescence of rare-earth ions and intrinsic defects in Gd2O3 matrix

The X-ray luminescence and photoluminescence of the ultradispersed Gd2O3 powders with different purity were investigated in 90-360 K temperature range. Both impurity and intrinsic optical active centers were detected. The effect of energy transfer from Gd3+ to RE3+ ions was observed.

Luminescence of intrinsic localized states in alkali silicate glasses excited by pulsed electron beam

The exposure of pulsed electron beam was applied for exciting the luminescence of two types of localized electronic states (so-called L-centers) in the Na2O-K2O-CaO-SiO2 glasses with varied Na/K relation. The recorded luminescence spectra clearly exhibit the line-type fine structure. It was shown that this fine structure of spectra reflects the interaction of electron excitations both with local vibrations of nonbridging oxygen atoms and with phonon modes of the glassy network during the radiative relaxation of the triplet state of L-centers. The appearance of additional “mixed” vibrations discussed and interpreted in terms of the expanded model of an L-center.

Photoluminescence of Gd2O3:Er – based materials for conversion of solar energy

The spectral and luminescence properties of Er3+ activated Gd2O3 compacted powders have been investigated. There are several excitation channels of Er3+ luminescence: interband transitions, the energy transfer from Gd3+ ions and intracenter excitation. The quantum efficiency of the Er3+ ions luminescence under different excitation was calculated.

Photoluminescence of implantation-induced defects in SiO2:Pb+ glasses

The luminescence of quartz glass with implanted Pb+ ions is investigated by time-resolved photoluminescence spectroscopy under synchrotron excitation. It is established that the glass layer modified with ions represents a microheterogeneous medium with a variable content of implanted ions predominantly in the form of Pb2+. Three different types of emission centers are detected that are created by radiation-induced defects of the SiO2 matrix and localized electronic states of the amorphous lead-silicate phase.