K. Wisniewski

Excited state spectroscopy of chromium ions in various valence states in glasses

Abstract The spectral properties of different types of chromium-activated glasses are shown, discussed and interpreted. Chromium in four valence states, Cr 3+ , Cr 4+ , Cr 5+ and Cr 6+ , is seen in the spectral characteristics of these glasses where Cr 3+ , Cr 5+ and Cr 6+ play an important role. Trivalent chromium in octahedral coordination reveals the spectra and decays that are typical for low-field materials with a substantial participation of the site-to-site disorder. The characteristics of the Cr 5+ and Cr 6+ ions appeared to be more interesting. Absorption, excitation and luminescence of the pentavalent chromium (d 1 system) in the octahedral coordination are severely affected by the Jahn–Teller effect, along with the nuances associated with that effect. The hexavalent chromium (d 0 system) in the four-fold coordination, forming the [CrO 4 ] 2− group, is seen mostly in the excited state absorption (ESA) spectra that can be interpreted in terms of the transitions between crystal field split terms of the Cr 5+ O − centre, which forms after the charge transfer (CT) transition, and between one of those terms and another double-electron state of larger electron lattice coupling, which forms after two consecutive transitions of electrons via the CT transition.

Continuous function decay analysis of a multisite impurity activated solid

The technique of continuous function decay analysis, previously used in studies of molecular dynamics, is applied to a solid that is optically activated through impurity doping. Chromium ions occupy several different sites in gahnite glass ceramics, each of which has different luminescence lifetime characteristics but overlapping absorption and emission spectra. Continuous function decay analysis maps the decay patterns of the decaying species, producing histograms of the relative strengths of decay at (in this case) 125 logarithmically spaced lifetimes. The results for chromium ions in gahnite glass ceramics are related to the interaction between the impurity ions and the solid state environment and correlate well with previous studies of this material that have used standard techniques. Continuous function decay analysis is thus shown to be an effective method for understanding the optical behaviour of multisite materials.

Excited state absorption in chromium doped Li2B4O7 glass

Excited state absorption (ESA) measurements of the Cr:Li2B4O7 glass (Cr:LBO-glass) along with preliminary interpretation are presented. The presence of chromium in its tri- (d3) and hexa- (d0) valence states is observed. Both Cr3+ and Cr6+ ions appear to contribute in the de-excitation processes and can be attributed in the ESA spectra under excitation wavelengths at 308 nm, 488 nm, 515 nm and 610 nm. The ESA spectra detected with UV excitation have been interpreted in terms of transitions in the framework of the Cr5+O- centre, which forms after charge-transfer-type absorption in the [CrO4]2- group. Assumption of the double-electron state of the 3d22p4 electronic configuration together with crystal-field-split states of the 3d12p5 configuration allowed us to reproduce the obtained ESA spectra. The ESA spectra of the Cr3+ ions have different characteristics and are related to transitions to the conduction band.

Excited state spectroscopy of the silica sol–gel glass activated by Cr5+ and Cr6+ ions

We report on the optical spectroscopy of the silica sol–gel glass doped with chromium of various valences where Cr6+ and Cr5+ ions appear to be most active. The presence of the Cr5+ ions in six-fold coordination is seen in the luminescence spectra and decays whereas the Cr6+ ions in four-fold coordination are mostly responsible for the excited state absorption (ESA), but also give a contribution to the luminescence. We interpret the ESA in terms of transitions between crystal field split terms of the Cr5+O− centre which forms after the charge transfer (CT) transition, and between one of those terms and another, double-electron state of larger electron–lattice coupling, which forms after two consecutive transitions of electrons via the CT transition. The luminescence and decay characteristics are due to the composition of the transitions in both Cr5+ and Cr5+O− centres, the former interpreted in terms of the Jahn–Teller effect in the d1 system in the octahedral coordination, along with the nuances associated with that effect; the latter ones being the triplet–singlet or singlet–singlet transitions depending on temperature.

Excited state absorption in materials containing Cr3+ and Cr4+ ions

Abstract The ground state absorption (GSA), the excited state absorption (ESA) and fluorescence properties (low- and room temperature emission spectra) of Cr 3+ , Cr 4+ -doped single crystals: Y 3 Al 5 O 12 (YAG) and SrGdGa 3 O 7 (SGG) have been studied at various temperatures in a broad spectral range (300–1700 nm). In the measured characteristics of those crystals we have observed features which could be ascribed to both Cr 3+ and Cr 4+ . In this work, we put a special stress upon the ESA measurements. The measurements were performed by the continuous wave pump-and-probe phase-sensitive technique using an Ar-laser (excitation directly into the ion) and tungstate lamp, and by pulsed technique using an excimer laser (UV excitation) and Xe-flash lamp. Relations between spectral responses of the Cr 3+ and Cr 4+ ions in different matrices under various excitations are observed and discussed.

LUMINESCENCE AND LUMINESCENCE KINETICS OF CHROMIUM DOPED GAHNITE GLASS CERAMICS

Abstract The fluorescence decay kinetics of Cr 3+ impurity ions in a gahnite glass ceramic are analysed using a technique used previously in molecular spectroscopy that produces a continuous distribution of lifetimes rather than a number of discrete contributions. The results are shown to be consistent with Cr 3+ ions occupying three different phases within the host material. These phases are identified and shown to make different contributions to the fluorescence spectra of the material. Examples are given for different combinations of excitation and fluorescence detection wavelengths and for different sample temperatures.

Optical spectroscopy and multiple-line gain in Pr3+-activated fluoroaluminate glass

We demonstrate the results of excited-state absorption measurements that reveal optical gain at several lines due to triplet–triplet transitions in Pr3+ ions in a fluoroaluminate glass host. Gain around 589 nm is especially attractive for laser applications in the area of satellite communication. The multiple-line character of the gain as well as the broadening of these lines is very promising because it can make possible the creation of a widely tunable solid-state laser. The gain measurements are complemented by systematic measurements of the basic spectroscopic characteristics of Pr3+ in the fluoroaluminate glass host, where we demonstrate the role of energy transfer and nonradiative transitions in the deexcitation process. The latter is associated with a defect state in the glass host.

An a analysis of the tragic events which occurred at an inauguration party organized by the student government of the University of Science and Technology in Bydgoszcz during the 2015/2016 academic year

In this article, the authors analysed the tragic events which took place at an inauguration party organized by the student government of the University of Science and Technology in Bydgoszcz during the 2015/2016 academic year. As a result of crowd panic which occurred during “initiation ceremonies”, three young students died.