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Abstract: The bismuth tellurite Bi2TeO5 (BTO) single crystal exhibits nonlinear properties. Doped with rare earth ions can be potential laser and self-frequency doubling generation (SFDG) material. Crystals are grown by the Czochralski method. Optical properties of the Yb3+:Bi2TeO5 single crystal are reported. Absorption, emission and luminescence decay measurements were carried out at 6K and 300K. The existence of different ytterbium site positions was observed and analysed. The attempt was made to assess the potential laser properties of the Yb3+:BTO material; polarised absorption cross-sections and stimulated emission cross-sections are presented. [Copyright &y& Elsevier]

Abstract: Spectroscopic characteristics of and in , and fluoride matrices are considered. Crystal structures of these compounds have been ascertained based on X-ray measurement on single crystal samples. Energies of lattice vibrations have been derived from IR and Raman spectra. Spectroscopic features of crystals in the VUV region were studied using experimental facilities of the Superlumi station at HASYLAB in Hamburg. High-resolution spectra and decay curves of luminescence in the visible were used to determine the energy levels and excited state relaxation dynamics of luminescent ions. Relevance of energy transfer processes, which feed the levels of and the level of , is discussed. [Copyright &y& Elsevier]

Abstract: In the luminescence of europium is quenched by the presence of . Analysis of the decay curves of the and luminescence, recorded at room temperature, suggests that the emission is quenched by quadrupole–quadrupole interaction with multiplet of praseodymium. The generalized Yokota–Tanimoto model has been used to explain the behavior of the decay curves and to determine the kinetic microparameters , related to the cross relaxation, and D, related to the energy migration probabilities. The “critical radius” for these interaction was calculated to be in the range 10.007–11.528Å. [Copyright &y& Elsevier]

Abstract: A heavy metal oxide borate glass with composition (70−x)PbO–18B2O3–6Al2O3–3WO3 (wt%) was modified by variable content of PbF2 (, 36 and 72wt%) and doped with 1wt% of Pr3+ or Tm3+ ions. The influence of the PbF2 content on optical properties and luminescence dynamics has been observed through the variation of an effective line width of 1D2→3H4 and 1G4→3F4 emissions as well as the 1D2 and 1G4 lifetimes of Pr3+ and Tm3+, respectively. It was observed that the increase of PbF2 content leads to narrowing of the 1D2→3H4 band from 680 to 590cm−1. This effect was not observed for the 1G4→3F4 thulium emission. The variation of luminescence kinetics was observed both for Pr3+- and Tm3+-doped samples; the increase of the PbF2 content has changed the 1D2 lifetime from 13.8 to 16.5μs and from 34 to 43μs for the 1G4 level. [Copyright &y& Elsevier]

Tm3+-Eu3+ energy transfer processes and relaxation dynamics of the 3 H 4 and 3 F 4 excited states of Tm3+ ions in 1 at. % Tm3+, 5 at. % Eu3+:YVO4 single crystal were studied. Contribution of Tm3+-Eu3+ energy transfer reduces effectively the lifetime of terminal level in a potential 3 H 4–3 F 4 laser transition at around 1.48 μm. Adverse quenching of the 3 H 4 emission by Eu3+ ions is found to be less efficient than that reported for Tm3+ + Tb3+ system in YVO4. The classical Inokuti–Hirayama model accounts well for an experimental decay curve of the 3 H 4 emission recorded for co-doped crystal. Stimulated emission cross section for 3 H 4–3 F 4 transition of Tm3+ at around 1.48 μm was analyzed taking into account the anisotropy of YVO4 crystal. [ABSTRACT FROM AUTHOR]

The relevance of processes contributing to depletion of pump and upper laser levels has been assessed based on experimental data obtained during measurement of excited state absorption, steady state emission and dynamics of excited states as a function of excitation power and activator concentration. It has been concluded that the excited state absorption in YVO4: Nd and YVO4: Er is not significant except for that from the 4 I11/2 level of Er3+. In these systems, the interionic processes are dominant. In particular, the reported decrease of the YVO4: Er laser slope efficiency when the Er3+ concentration increased from 0.5 to 1 at % is due mainly to the up-conversion by energy transfer from the pump level and upper laser level. Excited state absorption cannot contribute to depletion of excited states involved in the 3 F4-3 H6 laser operation near 1800 nm in the YVO4: Tm crystal. However, the heavy doping required to enhance the cross-relaxation process which feeds the upper laser level brings about the migration-accelerated energy transfer to energy sinks. [ABSTRACT FROM AUTHOR]

Abstract: Results of recent investigation aimed at finding new efficient laser active materials and converters of VUV radiation into visible emission are summarised. Representatives of two families of compounds with general chemical formulae: K5Li2LnF10 (Ln3+ =Ce, La–Gd) and M3LnF6 (M+ =K+, Cs+, Rb+; Ln3+ =La–Yb) as well as a new compound Na2K2NdF7 have been synthesised by a solid state reaction and next obtained in a single crystal form by the Bridgman method. Crystal structures of compounds have been ascertained based on X-ray measurement on single crystal samples. Spectroscopic properties of crystals have been determined based on optical absorption spectra, emission spectra and luminescence decay curves recorded at temperatures between 4.2 and 300K in the UV–VIS–NIR spectral region. Optical properties and material parameters relevant to application of the crystals will be presented and discussed. [Copyright &y& Elsevier]

The up-conversion of infrared radiation at 808 nm, emitted by a diode laser, into blue emission centered at 480 nm in 1 at.% Tm, 5 at.% Yb: YVO4; 1 at.% Tm, 8 at.% Yb: YVO4 and 2 at.% Tm, 5 at.% Yb: YVO4 has been studied. The highest intensity of blue emission is found for the 1 at.% Tm, 8 at.%Yb: YVO4 system. The power dependence of up-converted emission upon continuous-wave excitation as well as the time evolution of its intensity upon short-pulse excitation were found to be consistent with a two-step excitation mechanism in which the forward Tm3+–Yb3+ energy transfer is followed by the back Yb3+–Tm3+ energy transfer. The effect of dopant concentrations on the up-conversion process is interpreted taking into account dynamics of the excited states involved. [ABSTRACT FROM AUTHOR]

Optical properties of trivalent dysprosium doped lithium niobate crystal Dy:LiNbO3 are investigated at various temperatures. Polarised absorption, emission and lifetime measurements have been performed. The Judd–Ofelt theory, extended to anisotropic system, has been applied to evaluate the intensity parameters (Ω2,Ω4,Ω6), radiative transition rates Ar, radiative lifetimes τr, and branching ratios β. The predicted values of τr is compared with the experimental value for the 4F9/2 fluorescent level. Lifetimes and fluorescence dynamics were examined as a function of temperature and concentration of Dy3+ ions. [Copyright &y& Elsevier]

Abstract: Oxyfluoride glasses with composition 50GeO2–(50−x)PbO–xPbF2 (x⩽15mol%) containing praseodymium or thulium were melted from commercial raw materials in normal atmosphere. Glass samples were then thermally treated in order to achieve controlled precipitation of PbF2. The effect of thermal treatment on the relaxation of excited levels within 4fn configurations of praseodymium and thulium is found to be qualitatively similar. Non-exponential decay curves of luminescence in as-melted glasses become nearly exponential with corresponding longer lifetimes in thermally treated samples. Substantially different behavior of samples containing praseodymium with respect to those containing thulium has been found upon excitation in the 50–300nm spectral region. Efficient VUV-excited visible emission has been recorded with both as-melted and thermally treated glass containing Pr3+. No visible emission has been recorded upon VUV excitation of glass and glass-ceramics samples containing thulium. [Copyright &y& Elsevier]

Spectroscopic properties of the Dy3+-doped YAl3(BO3)4 crystal were studied from the vacuum-ultraviolet to near-infrared spectral range. Optical results were interpreted in terms of the 4fn, 4fn-15d and charge transfer transitions. It was found that the VUV electronic excitation is transferred to the optically active ions giving emission from the 4F9/2 fluorescent level of Dy3+. The temperature variation of the Dy3+ fluorescence kinetics was observed; the 4F9/2 lifetime increased with increasing temperature. This phenomenon is not usually observed in other rare-earth-doped media. The discussion of dysprosium emission properties and their temperature dependency was based on the assumption that the rates of transitions originating in individual crystal field levels of the 4F9/2 emitting multiplet are significantly different. [Copyright &y& Elsevier]

Unusually intense vibronic sidebands appear in the 4.2 K absorption spectra corresponding to transitions to sextet states 6FJ (J=1/2–9/2) of Sm3+ in K5Li2SmF10 single crystal. R value defined as the ratio of integrated intensity of vibronic sideband and the integrated intensity of no-phonon lines has been estimated to be as high as 2.64 for the 6H5/2–6F7/2 transition. Contribution of vibronics to transitions to quartet states is negligible. Instead, the electron–phonon coupling induces strong thermal line broadening as evidenced by temperature dependence of line widths associated with the 4G5/2–6H5/2 transition, consistent with the electron–phonon coupling parameter α∼500 cm−1. [Copyright &y& Elsevier]

Single crystals of K5Li2La1−xEuxF10 (where x=0.01,0.03,0.1,0.25,0.50,1) have been obtained from anhydrous fluorides by solid state reaction and then by the Bridgman crystal growth process. Optical properties of crystals were investigated at various temperatures between 5 and 300 K. Energy level scheme for Eu3+ has been constructed based on absorption and emission spectra recorded at 5 K. Emission from 5D3, 5D2, 5D1 and 5D0 levels has been studied in detail. It has been found that emission originating from the 5D0 and 5D1 levels is efficient and long lived for all Eu3+ concentrations. Estimated selfquenching rate of the 5D1 luminescence is as small as about 103 s−1 in K5Li2EuF10. Temperature dependence of this selfquenching is found to be consistent with a cross-relaxation process in which a donor ion makes the 5D1–5D0 transition and an acceptor ion makes the 7F1–7F3 transition. The 5D2 luminescence is considerably strongly influenced by activator–activator interaction but it is still easily detectable. The 5D3 luminescence is completely quenched in K5Li2EuF10. [Copyright &y& Elsevier]

Single crystals of erbium-doped La 3 Ga 5.5 Ta 0.5 O 14 , grown by the Czochralski method, have been investigated using methods of optical spectroscopy. Room-temperature absorption spectra were analysed in the framework of the Judd-Ofelt theory. Radiative transition rates, radiative lifetimes and luminescence branching ratios for luminescent levels of Er 3+ have been evaluated and compared to measured luminescence intensities and lifetimes. The laser potential associated with the 4 I 13/2 - 4 I 15/2 transition near 1.55 μm has been assessed. It has been concluded that La 3 Ga 5.5 Ta 0.5 O 14 :Er crystal is an intermediate gain laser material exhibiting strong inhomogeneous broadening of absorption bands, advantageous for optical pumping with laser diodes. [ABSTRACT FROM AUTHOR]

The presence of hydroxyl ions in LaGaO 3 single crystals has been detected by means of Fourier Transform Infrared (FTIR) absorption spectroscopy. A single narrow absorption line of the OH - stretching vibration at about 3521 cm -1 has been observed at T  = 9 K in most of the as-grown crystals. The vibrational frequency decreased abruptly at the orthorhombic-rhombohedral structural phase transition temperature ( T c  = 418 K). The parameters of the anharmonic potential of the OH - stretching vibration have been determined from the isotopic replica and the overtone frequency and intensity, and found to be in agreement with those measured for hydroxyl ions in other oxide crystals. [ABSTRACT FROM AUTHOR]

The optical spectra of compounds containing trivalent rare earth (Re3+) ions often show vibronic features. The intensity of vibronic transitions is determined by the strength of the electron–phonon (ion–lattice) coupling and depends strongly on the rare earth and the host lattice.In this paper we report on electron–phonon coupling in the GdCOB system doped with Eu3+, Tb3+ and Yb3+ ions. According to general theory intense vibronic lines are to be expected for electronic transitions with ΔJ=0, ±2 and these transitions were mainly considered in this paper for both Eu3+ and Tb3+ ions. In the case of Yb3+ ions, a strong vibronic sideband belongs to the 2F7/2→2F5/2 transition with ΔJ=1 although it seems to be in contradiction to the general selection rule.The vibronic features observed in absorption, excitation and emission spectra were analysed on the basis of the host lattice modes obtained from Raman and the far infrared spectra of the matrix. [Copyright &y& Elsevier]

Crystals of YVO[sub4]:Ho were grown by the Czochralski method. The structure of the low-energy levels of Ho&sup3+; has been estimated experimentally. Intensity parameters, radiative lifetimes, and branching ratios have been calculated in the framework of the Judd-Ofelt theory. The influence of temperature on luminescence lifetimes has been investigated. The calculated nonradiative transition rate was compared with the energy-gap law. The potential laser gain for the &sup5;I[sub7]-&sup5;I[sub8] transition has been estimated. [ABSTRACT FROM AUTHOR]

Abstract. Absorption, excitation, and emission spectra of trivalent thulium in SrGdGa[sub 3]O[sub 7] crystal have been recorded at room temperature and at approximately 8 K. Room-temperature luminescence lifetimes of [sup 1]D[sub 2], [sup 1]G[sub 4], [sup 3]H[sub 4], and [sup 3]F[sub 4] states have been measured for Tm concentration ranging from 0.5 at. % to 9 at. %. Based upon these data the crystal field splitting of luminescent states has been derived and radiative transitions rates have been evaluated. Strong self-quenching of luminescence originating in the [sup 1]G[sub 4] and [sup 3]H[sub 4] states has been found in this activator-host combination. Peak emission cross section of the potential laser transition at 1800nm was determined to be 3.9 x 10[sup -21] cm[sup 2] and the gain coefficient versus wavelength was estimated and discussed. [ABSTRACT FROM AUTHOR]

Single crystals of SrLaAlO: Pr and SrLaAlO: Nd have been grown by the Czochralski method and their optical properties have been studied for different activator concentrations. The absorption and emission spectra of the activators are inhomogeneously broadened because the Sr and La ions are distributed randomly on the sites of C symmetry, however, the symmetry selection rules are still obeyed. Strong self-quenching of the praseodymium luminescence occurs by cross relaxation which is supposed to be assisted by phonon emission in the case of the P level. Self-quenching of Nd luminescence disappears at low temperature indicating that the condition of resonance in the cross-relaxation process is fulfilled only for higher components of the ground state. [ABSTRACT FROM AUTHOR]

Abstract: Single crystal of (Lu0.2Gd0.78Ce0.01Sm0.01)2SiO5 (LGSO:Ce,Sm) was grown by the Czochralski method at a temperature ca 1795°C. It has been found that the crystal retains the structure of the C2/c space group inherent in Lu2SiO5 (LSO) compound. When illuminated by an UV light in the region 350–390nm it exhibits an intense visible emission whose spectrum stretches from ca 400nm to 650nm and consists of a broad band Ce3+ luminescence and of much narrow bands of Sm3+ luminescence excited mainly by the Ce3+–Sm3+ energy transfer. Observed pronounced effect of the excitation wavelength on colour of emitted light, due to changes of spectral characteristics of the Ce3+ contribution, was attributed to selective excitation of two different Ce3+ sites available in the crystal lattice. It has been found that the intensity of the visible emission decreases with increasing temperature and becomes negligibly small at about 100°C. [Copyright &y& Elsevier]

Abstract: Fluorescence at 1.06μm due to main 4F3/2–4I11/2 laser transition of Nd3+ ions in multicomponent B2O3–PbF2–PbO–Al2O3–WO3 glass system has been registered and some laser parameters for Nd3+ ions have been evaluated. The Nd-doped oxyfluoroborate glasses have been investigated as a function of PbF2 concentration and thermal treatment. The fluorescence decays from 4F3/2 excited state of Nd3+ ions are independent on PbF2 concentration. The orthorhombic PbF2 phase has been identified for Nd-doped transparent glass-ceramics obtained after thermal treatment. [Copyright &y& Elsevier]