Czeslaw Koepke

Excited state absorption in Cr3+-doped gahnite glass ceramics

Abstract We report on the excited state fluorescence and absorption characteristics of chromium-doped gahnite glass ceramic. The material is characterized by a very structured and wide emission spectrum despite its lowest excited state being the doublet 2 E g , usually associated with very weak electron–phonon coupling. Excited state absorption is principally from the doublet 2 E g to three higher-energy doublets though an additional contribution due to the gahnite glass ceramic host is also present during UV excitation. The chromium excited state absorption has been extracted from the overall spectrum. Utilizing data from the emission, absorption and excitation spectra, the configuration coordinate diagram describing octahedrally coordinated Cr 3+ ions in the gahnite glass ceramic has been produced. From this diagram the expected excited state absorption spectrum, including the influence of bleaching, has been modelled and a comparison made with experimental data.

Optical spectroscopy and excited state absorption of the ZAS (ZrO2–Al2O3–SiO2) glass doped with chromium

Abstract We describe the general spectroscopic characteristics of the zirconia–alumino–silicate glass doped with chromium. The material displays all the features typical of trivalent chromium occupying weak field sites with spectral properties characteristic of the glass phase. In the excited state absorption (ESA) spectra features typical of chromium doped materials known from previously reported data are observed, although not all of them can be attributed to the Cr 3+ ions. The ESA spectrum, partially overlapping the emission range, appears to preclude lasing in the range 11300–14400 cm −1 , but for the energies lower than 11300 cm −1 a net gain can occur. Based on absorption and emission data a single configuration coordinate diagram is created which allows a predicted ESA spectrum to be compared with the experimental data.

Spectroscopy of lanthanum lutetium gallium garnet crystals doped with chromium

Lanthanum lutetium gallium garnet of the compositions La2.32Lu2.61-xCrxGa3.07O12 and La2.7Lu2.3-xCrxGa3.07O12 with various chromium concentrations was grown by the Czochralski method. We measured the luminescence, absorption excitation, and excited-state absorption spectra. Two different octahedrally coordinated low field Cr3+ centers were found in crystals of both compositions. In the La2.7Lu2.3-xCrxGa3.07O12 crystals an additional absorption found in the region 13 000–16 000 cm-1 is attributed to the tetrahedrally coordinated Cr4+ system.

Changes in optical properties of YAG:Ce single crystals due to codoping and ionizing radiation treatment

Absorption, luminescence, ESR and ESA spectra and TL glow curves of YAG:Ce crystals codoped with Mg2+ ions and subjected to various treatments have been measured. The variations induced by irradiations in gamma and proton beams, and by thermal annealings under oxidation and reduction conditions point to large variations of the cerium ion valency. The ESA spectra of Mg-free and Mg-codoped crystals are clearly different with the peak value in the YAG:Ce, Mg sample higher and shifted towards the shorter wavelengths. Although the TL glow curves reveal the existence of the same major traps in both materials, their role in the overall deexcitation process is strongly modified upon Mg-codoping.

Optical properties of Li2B4O7 glasses doped with rare-earth and transition-metal ions

Absorption and emission spectra of Cr, Eu and Dy ions in Li2B4O7 glasses melted in oxygen and hydrogen were measured for valency states and excited states analysis. It was stated that the presence of Cr6+ ion is limited by composition of the starting mixture and atmosphere of the melting and that this ions arises as Cr6+O4 complex.

Structure of the 2Eg-4A2 emission of the Cr3+: gahnite glass ceramics

The spectroscopic characteristics of chromium-doped gahnite glass ceramics have been evaluated. The material exhibits multi-site spectra, including a complicated emission spectrum and room temperature anti-Stokes emission. Careful analysis of the room and low temperature spectra, supported by luminescence decay measurements, proves the existence of a t least two high-field sites associated with single Cr3+ ions and pairs of Cr3+ ions. The R line of the highest field sites is accompanied by phonon side bands. Estimates of the associated phonon energies have also been made.

Up-converted emission and mode beating in Er 3+ - doped fibers

We demonstrate the differences in the excited state transmission (EST) for different modes in 8 μm core diameter, Er(3+)- doped silica fiber. The S(2) (Spatially and Spectrally resolved) imaging method was used to determine the modal composition of the transmitted beam and to analyze the group delays of the higher order modes. We register the up-converted emission under two beam excitation (980 nm + 850 nm or 790 nm) and propose the numerical model for the anti-Stokes emission analysis. Taking additionally into account the interference of the beating fiber modes, one can expect the inhomogeneous spatial distribution of the excited ions. This was predicted by numerical calculations. The obtained results have been confirmed by taking photo of the up-converted emission as seen from the side of the fiber.

ASE noise independent small signal modal gain measurements and mode imaging in double clad Nd 3+ - doped fiber around 900 nm

The spatially and spectrally resolved mode imaging method (S²) and lock-in detection technique are combined to allow for low signal gain measurements in double clad, Nd³⁺- doped fiber in the spectral region of 900 nm. The combination of these methods gives us the opportunity to measure the low signal gain, without disruption of the result by the amplified spontaneous emission (ASE). Results of the modal gain measurements are compared to numerical calculations.

Spectroscopic evaluation of titanium-doped glass

We have evaluated a prototype glass doped with titanium from the point of view of its basic spectroscopic characteristics. Measurements of the luminescence lifetime at various wavelengths, luminescence spectra and time resolved luminescence spectra have been performed. Using the obtained characteristics we have attempted to interpret the de-excitation mechanism in the Ti:glass. For sufficiently high excitation energy the luminescence involves the following centers: Ti3+, emitting at 780 nm, Ti4+, emitting at 460 nm and an unidentified luminescence center emitting at approximately 560 nm.

Electron-lattice interaction of localized states in solids

In this contribution we analyze the electron-lattice coupling in a case of localized orbital triplet states using the emission, absorption and the excited state absorption (ESA) spectra of the d degree(s) complexes in CaWO4 and CaMoO4 crystals. We consider coupling to a fully symmetrical one-dimensional mode as well as to (epsilon) and (tau) 2 Jahn-Teller (J-T) modes. Our method allows us to estimate the contribution of the J-T effect and coupling to the full symmetry breathing mode to the overall electron-lattice coupling energy. We also estimate anharmonicity of the lattice vibrations related to the spin-orbit coupling between the components of the luminescing triplet.