H. Przybylińska

Electronic structure of Ce3+ multicenters in yttrium aluminum garnets

Low temperature, infrared, and visible-ultraviolet absorption spectra of yttrium aluminum garnet (YAG) bulk crystals and epitaxial layers doped with Ce are presented. In the region of intra-configurational 4f–4f transitions, the spectra of the bulk YAG crystals exhibit existence of at least two different Ce3+ related centers, a major one associated with Ce in regular positions substituting yttrium and also additional center, due to so called antisite positions in the garnet host, i.e., ions in the Al positions. Crystal field analysis based on exchange charge model exhibit excellent agreement with the experimental data for major Ce3+ center.

Defect-mediated and resonant optical excitation of Er3+ ions in silicon-rich silicon oxide

Sensitization of the 4I13/2–4I15/2 Er3+ luminescence at 1.54 μm in silicon-rich silicon oxide (SRSO) is studied in the blue-green range. We show that defects due to excess Si in silica act as luminescence sensitizers. We also suggest that there exist two types of Er centers—isolated ones and others—strongly coupled to defects. In SRSO competition of direct, resonant excitation of Er3+ and indirect processes via defects is observed. Enhancement of the Er emission for off-resonant excitation does not seem to compensate losses in the direct channel of excitation to the 2H11/2 state of Er3+. We suggest that the emission efficiency of Er3+ is limited by distance-dependent transfer rate and little spectral overlap of the interacting states.

On the determination of thermal ionization energy of deep centers from ESR data

It is shown that the skin effect due to thermal generation of free carriers may affect the ESR signal more than deep center depopulation. Experimental results for 0.33 eV deep Eu2+ donor in CdF2 crystals are presented, to show the way in which the thermal energy of deep centers is deduced from the ESR data.

Direct observation of localized impurity excited states degenerate with conduction band (CdF2: Eu)

Abstract On the basis of the coupled absorption, conductivity, thermoluminescence and ESR photoquenching experiments it is shown that all the excited 4f 6 5d states of Eu 2+ are degenerate with the conduction band of CdF 2 . This is a unique property of CdF 2 among other flourites.

Room-temperature photoluminescence excitation spectroscopy of Er3+ ions in Er- and (Er+Yb)-doped SiO2 films

We apply photoluminescence excitation spectroscopy to study the efficiency of excitation at 960–990 nm of the 1.54 μm emission of erbium implanted into SiO2 films thermally grown on silicon for a range of Er and Yb concentrations. We show that, in silica films doped solely with Er, the concentration of Er should be lower than 1020 cm−3 to prevent efficient concentration quenching of the emission. It is shown that the Yb/Er concentration ratio of 1–2 is optimum for the dopant densities of 1–2×1020 cm−3, whereas 1021 cm−3 results in quenching of the emission due to energy losses within the Yb subsystem.

Reduction of Tb4+ ions in luminescent Y2O3:Tb nanorods prepared by microwave hydrothermal method

Abstract Terbium doped yttrium oxide was prepared with the microwave hydrothermal method. The Y 2 O 3 :Tb nanomaterial crystallized as needle-like grains. Bright luminescence in the green region was observed. Significant luminescence intensity increase was obtained after thermal treatment. Reduction of terbium ions was observed after heating in the air atmosphere. Tb 4+ ions were found to be stabilized by crystal impurities. Hydroxyl species were found to have impact on vacancies elimination. The terbium ions were used as optical and magnetic indicator of the material properties.

The role of oxygen in optical activation of Er implanted in Si

Abstract The results of high resolution photoluminescence studies of erbium-implanted Czochralski-grown (CZ) and float-zone (FZ) silicon are presented. We show that the photoluminescence (PL) spectrum of cubic Er centers observed in CZ Si annealed at 900 °C is the dominant emission in FZ Si for the same annealing conditions. We assign it to an isolated interstitial erbium site and not to an octahedrally coordinated ErO complex. We resolve the PL lines of two ErO related centers with lower site symmetry (not found in FZ Si). The internal PL efficiency of the ErO defects is probably higher than that of isolated centers; however, the overall PL yield is rather controlled by the rate of energy transfer from excitons recombining at Er sites.

Magneto-optical study of Er+3-related center in selectively doped Si:Er

Photoluminescence at λ=1.54μm from an Er3+-related center dominant in a sublimation MBE-grown multi-layer Si/Si:Er structure is investigated in magnetic fields up to 6T. The magnetic-field-induced splitting is observed for all the main lines of the Er-related photoluminescence spectrum. For the most intense emission line, angular dependence of the splitting is measured in the (011) crystallographic plane of the sample. The effective g-tensor, corresponding to the difference between individual g-tensors of the lowest multiplets of the ground and the first excited states, is experimentally determined. In this way the symmetry of the Er-related optically active center dominant in the structure is found to be orthorhombic I (C2v). From temperature dependence of the intensity of the magnetic field split components, individual g-tensors of the ground and the excited states are separated. No influence of the growth direction on the symmetry of Er-related center was found.

Deep Rare Earth (RE) ions related energy levels in ZnS

Abstract An analysis of RE 2+/3+ energy level positions in ZnS is presented. It is shown that the concepts of Jorgensens refined spin-pairing energy theory (RESPET) may be extended to charge transfer ( sulfur → RE ) transitions in ZnS:RE. The theoretical results are verified by photo-electron spin resonance (ESR) studies of 3+ → 2+ photoionization transitions of Eu and Yb in ZnS. It is shown that the 4f-4f luminescence excitation spectrum of Yb 3+ has a photoionization nature. The arguments for the binding of a deep exciton by RE 3+ complexes are presented and discussed.

Novel excitation mechanism of rare earth intra-shell emission

Abstract A novel, highly efficient excitation mechanism of RE 3+ emission, proceeding via the RE 3+ photoneutral transition is reported on the example of Yb in ZnS single crystals.