Spectral and mechanical strength properties of Yb 3+ ,Li + :ZnWO 4 crystals were investigated, diode-pumped ZnWO 4 laser with an output power of 2,41 W was demonstrated.

${T m}^{3+}, \mathbf{L i}^{+}: \mathbf{Z n W O}_{4}$ single-crystal was grown by the Czochralski (Cz) method. The actual concentrations of the dopants were measured. Dispersions and temperature coefficients of the refractive indices (RI), as well as the mechanical strength characteristics of the crystal were measured. Spectroscopic studies of the crystal were carried out. The first laser operation above 2 $\mu \mathrm{m}$ at this crystal was obtained.

Erbium photoluminescence in GaN:Er was studied with above-band-gap excitation, provided by a He–Cd (λ=325nm) laser and below-band-gap excitation by a tunable Ti–Sa laser. The spectra obtained with these two lasers exhibit different spectral shapes. When both lasers are used at the same time, we observe that the Er3+ photoluminescence induced by each of the lasers is partly quenched by the illumination of the other laser. In this experiment, one of the lasers is modulated and a lock-in amplifier is used to filter the corresponding photoluminescence signal. The spectra recorded this way are found to be linear combinations of spectra obtained with each of the lasers used separately. This effect is explained by the presence of defects mediating the excitation towards the Er3+ ions. These defects act as electron traps, which can be populated by one specific laser excitation and are photo-ionized by the other laser leading to a large quenching of Er3+ emission.

Photoluminescence (PL) spectra, luminescence dynamics and luminescence saturation of the Er 3+ 4 I 13/2 → 4 I 15/2 transition in Er-implanted GaN samples at 7K are investigated. Under below-gap excitation, different Er centers are identified. Several Er centers are clearly excited via local defects or impurities. Er-defect complexes excited by above or below bandgap light are compared. Luminescence dynamics study shows that the 4 I 13/2 manifold has a shorter lifetime when Er ions are part of Er-defect complexes than when Er ions are isolated from any defect. The saturation of Er luminescence is investigated for the different types of Er center corresponding to specific excitation wavelengths.

Ferroelectric lead zirconate titanate (PZT) thin films have been prepared by chemical solution deposition (CSD) and were spin-coated onto stainless steel substrates. In order to improve the ferroelectric properties, the influence of an additional layer of strontium ruthenium oxide (SrRuO3) at the interface between the perovskite type PZT and the metal substrate has been studied. The elaboration route of the SrRuO3 thin films by CSD and spin-coating is presented. The influence from the annealing temperature on the PZT crystallization behavior has been analyzed by X-ray diffraction, and the PZT coercive field and remanent polarization were investigated as a function of the SrRuO3 process parameters. The results are compared with those obtained for PZT/RuO2/metal thin film capacitors.

Photoluminescence (PL), photoluminescence excitation (PLE) spectra and luminescence decay of the Er3+ 4I13/2→4I15/2 transition are investigated at 7K in Er-implanted GaN samples. Under below-gap excitation, PL and PLE spectra reveal the existence of two types of Er centers. One type of Er center which can only be excited by resonant intra 4f shell transition is predominant while other Er centers are clearly excited via local defects. Evolution of Er luminescence as a function of implantation dose and implantation geometry is presented for both types of Er centers. Luminescence dynamics study shows that the 4I13/2 manifold has a shorter lifetime (τ∼1ms) when Er ions are part of Er-defect complexes than when Er ions are isolated from any defect (τ=3.8ms). This result indicates the existence of non-radiative energy transfers in Er-defect complexes from Er ions towards defects or impurities. Er decay in Er-defect complexes is then successfully compared with classical energy transfer models.

Garnet crystals of the composition Gd3Ga5O12:Nd3+ (concentration series C-Nd = 1-10 at. %) were grown from flux. In terms of spectroscopy, these crystals, unlike those grown from melts, form a medium with a single activator center. For the first time, continuous-wave lasing was excited by diode pumping with the use of Gd3Ga5O12:Nd3+ crystals at the wavelengths lambda(3) = 1.3315 and lambda(4) = 1.3370 mum of the F-4(3/2) --> I-4(3/2) channel and also the simultaneous generation at two wavelengths, lambda(1) = 1.0621 and lambda(2) = 1.0600 mum, of the F-4(3/2) --> I-4(1/2) channel. (C) 2002 MAIK "Nauka/Interperiodica".

Garnet crystals of the composition Gd3Ga5O12:Nd3+ (concentration series CNd = 1–10 at. %) were grown from flux. In terms of spectroscopy, these crystals, unlike those grown from melts, form medium with a single activator center. For the first time, continuous-wave lasing was excited by diode pumping with the use of Gd3Ga5O12:Nd3+ crystals at the wavelengths λ3 = 1.3315 and λ4 = 1.3370 μm of the 4F3/2 → 4I13/2 channel and also the simultaneous generation at two wavelengths, λ1 = 1.0621 and λ2 = 1.0600 μm, of the 4F3/2 → 4I11/2 channel.

CW laser performance of Nd doped mixed-scandium-garnets in the 940 nm and 1060 nm regions is presented. Slope efficiencies at 1060 nm for the mixed garnets ranged from 47% to 59%, compared to 55% measured for Nd:YAG. The laser output was modeled taking into account the pump and laser mode overlap and divergence and compared to experimental results. Optimal laser performance was obtained when the pump and laser beam were of different sizes as predicted by the model.

We examine the laser possibilities offered by Tm 3+ -doped KY 3 F 10 . After crystal growth and X-ray diffraction analysis, the optical properties of thulium ions in KY 3 F 10 are determined for the first time. Absorption and emission spectra recorded at low temperatures are used to obtain a set of Stark sublevels, whereas the room-temperature absorption spectra have been allowed to fit the three phenomenological Judd-Ofelt (JO) parameters. The emission line strengths, branching ratios, and radiative lifetimes of levels from 3 F 4 up to 1 D 2 are then deduced. A comparison between the calculated lifetimes and the measured luminescence decay curves permits us to check the reliability of the JO analysis for this system. The potential of Tm:KY 3 F 10 for laser emission from 3 H 4 or 3 F 4 emitting levels is briefly examined.PACS Nos.: 42.55.Rz, 78.50.Ec, 78.47.+p, 81.10.Fq.

Fluorescence dynamics of the /sup 3/H/sub 4/ and /sup 3/F/sub 4/ energy levels of Tm/sup 3+/ ions in LiYF/sub 4/ single crystals codoped with Tb/sup 3+/ or Eu/sup 3+/ ions were experimentally investigated and confronted with classical energy-transfer models: direct cross-relaxation-type energy transfers between donor D and acceptor A, where D=Tm/sup 3+/ and A=Tb/sup 3+/ or Eu/sup 3+/ (static Forster-Dexter model extended by Inokuti-Hirayama) as well as energy migration between Tm/sup 3+/ ions (hopping and diffusion models by Burshtein and Yokota-Tanimoto). The fluorescence decays were accurately described in the case of Tb/sup 3+/ codoping because of resonant energy transfer, thus of more precise estimations of energy transfer parameters from the absorption and emission spectra. In the case of Eu/sup 3+/ codoping, the Tm/sup 3+//spl rarr/Eu/sup 3+/ energy transfers need to be phonon-assisted to compensate for the reduced overlap between the Tm/sup 3+/ emission and Eu/sup 3+/ absorption spectra and the models, though giving satisfactory results, appeared less powerful. Based on these results, optimized values for the dopant concentrations were finally derived to keep high the fluorescence quantum efficiency of /sup 3/H/sub 4/ and to shorten the lifetime of the /sup 3/F/sub 4/ energy levels of the Tm/sup 3+/ ion in order to alleviate the problem of self-termination of the /sup 3/H/sub 4//spl rarr//sup 3/F/sub 4/ laser transition occurring around 1.5 /spl mu/m.