M. M. Mezdrogina

Photoluminescence spectra of intracenter 4f transitions of rare-earth metal dopants in crystalline ZnO films

The influence of annealing in the medium of an ionized nitrogen, additionally introduced impurities, and regimes of post-growth annealing on photoluminescence spectra of intracenter 4f transitions of rare-earth metal dopants (Ce, Eu, Sm, Er, Tm, Yb) in crystalline ZnO films has been investigated. The films have been prepared using molecular-beam epitaxial growth and magnetron sputtering. According to the X-ray diffraction analysis, the films have a single-crystal structure. It has been shown that the annealing in the medium of an ionized nitrogen, regardless of the method used for producing the ZnO films, leads to significant changes in the photoluminescence spectrum, i.e., to a decrease in the emission intensity and a shift in the position of the emission maximum toward the long-wavelength range of the spectrum. The nitrogen concentration has been determined by the nuclear reaction method. It has been revealed that the spectra contain intense emission lines due to the intracenter 4f transitions of rare-earth elements (Sm, Er, Tm, Yb) in the crystalline ZnO films prepared by magnetron sputtering, and the intensity of the emission lines increases upon introduction of codopants, namely, Ce and Er.

Emission sensitization and mechanisms of electron-excitation migration in structures based on III-nitrides doped with rare-earth elements (Eu, Er, Sm)

The effect of doping with Eu, Er, and Sm rare-earth ions on the shape of the luminescence spectrum for heterostructures with GaN/InxGa1 − xN (0.1 < x < 0.4) quantum wells and from p-GaN〈Mg〉/n-GaN and p-AlGaN/n-GaN junctions is investigated. The results of measurements of the electroluminescence of these structures correlate with the previous data on photoluminescence and Mössbauer spectroscopy. It is shown that it is the GaN “yellow” (5000–6000 Å) band that plays the important role in the excitation of intracenter states in the structures with several GaN/InGaN quantum wells doped with Eu and Sm. In this case, Eu is most likely the sensitizer for Sm. Additional introduction of 3d metal (Fe57) in p-GaN〈Mg〉/n-GaN:Eu results in the realization of intracenter transitions in Eu3+: 5D0 → 7F1 (6006 Å), 5D0 → 7F2 (6195 Å), 5D0 → 7F3 (6627 Å), and 5D1 → 7F4 (6327 Å) due to the occurrence of new, efficient channels of excitation transfer to intracenter states and in the effect of Fe on the local environment of rare-earth ions including due to the f–d hybridization enhancement.

The effect of Fe, Cu, and Si impurities on the formation of emission spectra in bulk ZnO crystals

On the basis of the results of complex investigations (photoluminescence, x-ray fluorescence, and infrared spectroscopy), the features of emission-spectra formation are shown under the change in the type (Fe, Cu, and Si) and concentration of background impurities appearing during both growth and treatment of bulk crystals by grinding and polishing. Special attention is given to the concentration and types of bonds with hydrogen-the basic impurity preventing the formation of crystals with the p-type conductivity.

Effect of self-organization, defects, impurities, and autocatalytic processes on the parameters of ZnO films and nanorods

The effects of the parameters of ZnO-film deposition onto different substrates using the method of ac magnetron sputtering in a gas mixture of argon and oxygen hare studied. The phenomenon of self-organization is observed, which leads to invariability of the surface morphology of the ZnO films upon a variation in the substrate materials and deposition parameters. The parameters of the macro- and micro-photoluminescence spectra of the films differ insignificantly from the parameters of the photoluminescence spectra of bulk ZnO crystals obtained by the method of hydrothermal growth. The presence of intense emission with a narrow full-width at half-maximum (FWHM) in different regions of the spectrum allows ZnO films obtained by magnetron sputtering doped with rare-earth metal impurities (REIs) to be considered as a promising material for the creation of optoelectronic devices working in a broad spectral range. The possibility of the implementation of magnetic ordering upon legierung with REIs significantly broadens the functional possibilities of ZnO films. The parameters of the photoluminescence spectra of ZnO nanorods are determined by their geometrical parameters and by the concentration and type of the impurities introduced.

Effect of energy migration on the emission line shape in InGaN/GaN-based quantum-well structures

Structures with InGaN/GaN-based quantum wells and inhomogenetities in the lateral plane were used to study the effect of the mechanism of electronic excitation migration and carrier trapping on the formation of the emission line of the quantum wells. The stationary and time-resolved photoluminescence spectra were investigated over a wide spectral range under variation of the measurement temperature (4.2, 77, 300 K). The anisotropy (polarization) of radiation in InGaN/GaN structures with different inhomogeneities was studied. Excitation exchange among the inhomogeneities was shown to play an essential part in the formation of the emission line in a quantum-well system.

Intensity of visible and IR emission of intracenter 4f transitions of RE ions in Er- and Tm-doped ZnO films with additional Ag, Li, and N impurities

The use of Ag impurity in Er-doped ZnO films deposited by AC magnetron sputtering with a low growth rate has increased the emission intensity at λ = 1535–1540 nm. An increase in the deposition rate and in the temperature of substrates, as well as the use of Li and N+ impurities, led to a considerable increase in the intensity of the line with λ = 376–379 nm in the case of doping with rare-earth ions (Er, Tm), which makes it possible to use this semiconductor for creation of devices for the short-wavelength spectral region. Introduction of additional impurities in Er-doped ZnO films deposited on bulk ZnO crystals with increasing deposition rate and temperature caused an increase in the intensity of the line with λ = 1535–1540 nm. The photoluminescence spectra of ZnO films doped with Tm (ZnO) exhibited intense emission of lines with λmax = 377 nm.

Photoluminescence of nitro-substituted europium (III) phthalocyanines

Europium monophthalocyanine Eu(acac)Pc, europium monotetranitrophthalocyanine Eu(acac)Pc(NO2)4, and heteroleptic europium tetranitrobisphthalocyanine Eu(Pc)(Pc(NO2)4) are synthesized. The spectral characteristics of the phthalocyanine complexes in the visible and near-infrared regions are studied. The photoluminescence spectra are recorded. The luminescence bands are detected in the regions 450–500 nm (S2 → S0) and 670–730 nm (S1 → S0). The peaks are attributed to electronic transitions in the organic ligands.

Influence of europium doping on the sensitization of luminescence in GaAs/AlGaAs and InGaN/GaN quantum-well structures

A correlation between the photoluminescence spectra and structural parameters of Eu-doped quantum- well nanostructures InGaN/GaN and GaAs/AlGaAs is established. It is shown that the incorporation of rare-earth ions initiates lattice (as a rule, compressive) strains. The excitation migration in structures of high perfection stimulates transfer of nonequilibrium carriers to the 5D2-5D0 atomic levels of the Eu ion. In less perfect structures, the insertion of a rare-earth ion leads to the formation of isovalent traps in GaN layers capable of effectively capturing nonequilibrium carriers, which increases the intensity of photoluminescence of the structure by one order of magnitude.

Photoluminescence spectra of n-ZnO/p-GaN:(Er + Zn) and p-AlGaN:(Er + Zn) heterostructures

Luminescence intensity of heterostructures based on n-ZnO/p-GaN:(Er + Zn) and n-ZnO/AlGaN:(Er + Zn) is higher by more than an order of magnitude than the corresponding intensity of separate n-ZnO, p-GaN:(Er + Zn), and AlGaN:(Er + Zn) layers. Most likely, this phenomenon is due to the effective tunneling recombination of charge carriers caused by a decrease in the concentration of the nonradiative recombination centers located between the n-ZnO/p-GaN:(Er + Zn) and n-ZnO/AlGaN:(Er + Zn) layers.

Emission intensity of the λ = 1.54 μm line in ZnO films grown by magnetron sputtering, diffusion doped with Ce, Yb, Er

The effect of the Er3+-ion excitation type on the photoluminescence spectra of crystalline ZnO(ZnO〈Ce, Yb, Er〉) films is determined in the cases of resonant (λ = 532 nm, Er3+-ion transition from 4S3/2, 2H11/2 levels to 4I15/2) and non-resonant (λ = 325 nm, in the region near the ZnO band-edge emission) excitation. It is shown that resonant excitation gives rise to lines with various emission intensities, characteristic of the Er3+-ion intracenter 4f transition with λ = 1535 nm when doping crystalline ZnO films with three rare-earth ions (REIs, Ce, Yb, Er) or with two impurities (Ce, Er) or (Er, Yb), independently of the measurement temperature (T = 83 and 300 K). The doping of crystalline ZnO films with rare-earth impurities (Ce, Yb, Er) leads to the efficient transfer of energy to REIs, a consequence of which is the intense emission of an Er3+ ion in the IR spectral region at λmax = 1535 nm. The kick-out diffusion mechanism is used upon the sequential introduction of impurities into semiconductor matrices and during the postgrowth annealing of the ZnO films under study. The crystalline ZnO films doped with Ce, Yb, Er also exhibit intense emission in the visible spectral region at room temperature, which makes them promising materials for optoelectronics.