Valerii A. Smirnov

Yb-and Er-Doped single crystals of double tungstates NaGd(WO4)2, NaLa(WO4)2, and NaBi(WO4)2 as active media for lasers operating in the 1.0 and 1.5 µm ranges

Ytterbium-and erbium-doped single crystals of scheelite-like double tungstates NaGd(WO4)2, NaLa(WO4)2, and NaBi(WO4)2 and scheelite CaWO4 have been grown by the Czochralski method. The dopant concentrations in crystals are measured, and the coefficients of dopant distribution are determined to range from 0.45 to 3. The lifetimes of the Er3+ states 4I11/2 and 4I13/2 and the Yb3+ state 2F5/2 are measured, and the absorption and luminescence spectra of the crystals are studied in the vicinity of 1.0 and 1.5 µm. The data obtained are compared with the corresponding characteristics of other crystals. The possible use of the crystals studied as active media of solid-state lasers operating in the range 1.0 and 1.5 µm is discussed.

Effect of cerium codoping in Er3+,Ce3+:NaLa(MoO4)2 crystals

The detailed polarized spectroscopic investigation of I11∕24 and I13∕24 states of Er3+ ions in Czochralski-grown NaLa(MoO4)2 single crystals doped with Er3+ and codoped with Ce3+ as a function of cerium concentration is presented. The main results of room-temperature lifetime investigation show that the I11∕24 lifetime reduces by about 50 times from the solely Er-doped sample to the crystal codoped with 50at.% of Ce, while in the same experimental conditions, the lifetime of the I13∕24 level reduces by less than two times in the most heavily Ce codoped sample. This result looks very promising from the point of view of obtaining low-threshold 1.5-μm laser oscillation.

Growth and spectroscopic studies of NaLa(MoO4)2:Tm3+ crystals: A new promising laser material

Single crystals of scheelite-like disordered double molybdate NaLa(MoO4)2 doped with thulium ions with dopant concentrations of 3.0 × 1019 and 1.2 × 1020 cm−3 are grown by the Czochralski method. Spectral and luminescent studies of crystals grown are performed in wavelength ranges of 800 nm (the transitions 3H6↔3H4) and 2 μm (the transitions 3H6↔3F4), including the measurements of the polarized absorption and luminescence spectra of these crystals and the decay kinetics of their excited states. A model that satisfactorily describes the decay kinetics of the luminescence from the 3H4 level taking into account cross-relaxation interactions is proposed. The prospects for the use of these crystals as active media in two-micrometer solid-state lasers are discussed.

Growth and spectroscopic characterization of Er3+:CaWO4

In this work we present the growth and spectroscopic investigation of Er3+ in CaWO4 single crystals. Er3+ polarized absorption has been measured at room temperature from UV to 1700nm, and the fluorescence from the most important emitting states from the visible to the infrared has been recorded at 10 and 300K in the two possible polarizations. The lifetimes of the lower lying excited states have been measured as a function of the temperature to evaluate the contribution of nonradiative decay processes. The absorption spectra enabled us to determine radiative lifetimes of the emitting states by means of the the Judd-Ofelt approach. The stimulated emission cross section has been estimated for the 1.5μm transition. A comparison of the theoretical and experimental results permitted to obtain an estimate of the actual Er3+ doping level. A calculation of the effective gain cross section for the 1.5μm transition is also presented. These experimental results are discussed in order to evaluate the potentialities o...

Growth and spectral and luminescent properties of a new Cr4+:LiAlGeO4 nonlinear crystal

Single crystals of a new promising laser material, Cr4+-doped germanium eucryptite Cr4+:LiAlGeO4, are grown from the melt for the first time. The crystals grown exhibit nonlinear optical properties. Absorption and luminescence spectra of the crystals and their luminescence decay are studied at various temperatures. The luminescence lifetime at 1.2 μ m at 300 K is 10 μ s. Active centers in the crystal are identified, and crystal field parameters are estimated.

Determination of the charge state of chromium in Cr:Bi12GeO20 single crystals by spectral luminescence methods

The valence state and structural localization of Cr ions in Cr:Bi12GeO20 single crystals grown by the Czochralski method in air and annealed in argon or UV-irradiated have been determined in the spectral luminescence study. It is established that chromium is in the state of tetrahedrally coordinated Cr4+ ions in the samples studied. Octahedrally coordinated Cr2+ and Cr3+ ions and tetrahedrally coordinated Cr5+ ions were not revealed.

Spectroscopy of NaLa(MoO4)2: Tm3+ and NaGd(MoO4)2: Tm3+ crystals as advanced laser materials

Single crystals of double sodium-containing lanthanum and gadolinium molybdates doped with Tm3+ ions were synthesized by the Czochralski method. The spectroscopic properties of these crystals were investigated from the viewpoint of their use as active media in diode-pumped lasers. The polarized spectra of absorption on the 3H4 and 3F4 levels and the polarized spectra of luminescence due to the 3F4-3H6 laser transition were recorded, and the lifetimes of the 3H4 and 3F4 excited states of the Tm3+ ions were determined. The luminescence cross sections were calculated using the Füchtbauer-Ladenburg formula. The simulation of the decay curve of the 3H4 excited state according to the Golubov-Konobeev-Sakun method revealed that, in the crystals under investigation, the interaction between Tm3+ ions predominantly occurs through the dipole-dipole mechanism.

Spectroscopic characteristics of LiGaSiO4:Cr nano-glass-ceramics and glassy precursors

We have performed a complex of spectroscopic investigations (extinction, luminescence, and luminescence excitation spectra and luminescence decay kinetics) of LiGaSiO4:Cr nano-glass-ceramics and Cr-Li-Ga-Si-O glassy precursors. It has been shown that 94–96% of chromium in precursors synthesized in air are in the trivalent form, while remaining chromium is in the form of Cr6+ and Cr4+. The luminescence of the latter form in precursors at 300 K is strongly quenched. In precursors synthesized in an inert atmosphere, only trivalent chromium occurs. We have calculated the absorption cross sections of Cr3+ and Cr6+ ions in Cr-Li-Ga-Si-O glassy precursors. It has been shown that, in the case of synthesis of these precursors, a considerable amount of chromium is lost as a result of evaporation and fails to enter the specimens. Upon partial controlled crystallization of the precursors (formation of LiGaSiO4:Cr nano-glass-ceramics), the oxidation state of chromium that passed to crystallites from the glass phase becomes tetravalent. In this case, two types of luminescence centers arise, which correspond to Cr4+ ions localized in two different polymorphic modifications of LiGaSiO4. Spectral characteristics of these two centers (bandshape, peak position, and spectral range) are almost identical, whereas luminescence lifetimes are radically different.

Spectroscopic Investigations of Transparent Glass-Ceramics on the Basis of Cr 4+ :LiGaSiO 4

Single crystal of Cr4+-doped LiGaSiO4 was shown recently to be promising active medium of solid-state lasers tunable within 1.2-1.4 mum. This crystal demonstrates intensive broadband fluorescence with the lifetime 15 musec. The substantial evolution of the optical absorption spectrum after devitrification had been observed in the range of 600-800 mum. The formation of grains of chromium doped crystalline alpha-LiGaSiO4 phase, responsible for this fluorescence, was proved also by XRD and SEM measurements.

Degradation of the electronic excitation of the 4F3/2 state of Nd3+ ions in a γ-La2S3 single crystal

An investigation is made of processes of population and relaxation of the 4F3/2 neodymium upper active level in a γ-La2S3 semiconductor single crystal and the energy transfer microparameters are determined. Nonradiative transfer of energy from a continuous set of traps to the 4F3/2 upper active level of neodymium was observed when the sample was excited with λ = 0.53 μ radiation and cross relaxation from excited states located above the 4F3/2 upper active level was identified.