P A Ryabochkina

Intensities of hypersensitive transitions in garnet crystals doped with Er3+ ions

We examine the oscillator strengths and the intensity parameters Ωt (t = 2, 4, 6) of yttrium-aluminum, scandium-containing, and gallium garnet crystals doped with Er3+ ions. A comparative analysis of the oscillator strengths and the intensity parameters Ωt (t = 2, 4, 6) of garnets with different contents of Al3+ and Sc3+ ions (Gd2.4Er0.5Sc1.8Al3.3O12, Gd2.4Er0.5Sc1.9Al3.2O12, Gd2.4Er0.5Sc2.0Al3.1O12) is performed, as a result of which the oscillator strengths and the intensity parameters Ωt (t = 2, 4, 6) of these crystals are shown to have close values. We find that Ca3(NbGa)5O12 crystals doped with Er3+ ions are characterized by highest values of the oscillator strengths for hypersensitive transitions and of the intensity parameter Ω2 of Er3+ ions compared to the values of these quantities in the examined garnet crystals, which is determined by the fact that the symmetry of the local environment of Er3+ ions in these crystals is C1, C2, or C2ν. We reveal that, as the concentration of Er3+ ions in these crystals increases from 1 to 39 at %, both the oscillator strength of the hypersensitive transition 4I15/2 → 2H11/2 of Er3+ ions and their intensity parameter Ω2 tend to decrease, which can be related to an increase in the relative fraction of Er3+ ions with higher symmetry of the local environment.

Intensity parameters for Er3+ ions in calcium-niobium-gallium garnet crystals

Based on the analysis of the absorption spectra of Er-doped calcium-niobium-gallium garnet (Er:CNGG) crystals according to the Judd-Ofelt theory, the intensity parameters for these crystals are determined to be Θ2 = 3.43 × 10−20 cm2 Θ4 = 1.20 × 10−20 cm2, and Θ6 = 0.58 × 10−20 cm2. The parameters found are compared with the intensity parameters for other laser oxide crystals. Using these intensity parameters, the probabilities of radiative transitions between the energy levels of Er3+ ions in CNGG crystals and the luminescence branching ratios βJJ’ are calculated. From the measured lifetime of the 4I11/2 level of Er3+ ions (τ = 626 μs) and the probability of the radiative transition from this level (A = 192 s−1), it is found that about 88% of the excitation energy in the Er:CNGG crystals is nonradiatively transferred from the 4I11/2 to the 4I13/2 level. It is suggested that an increase in the oscillator strength and in the line strength of the 4I15/2 → 2H11/2 transition of Er3+ in CNGG crystals, as well as an increase in the intensity parameter Θ2 with respect to the corresponding parameters for other garnet crystals are caused by the existence in CNGG crystals of Er3+ centers with the environment symmetry lower than D2.

Growth, optical parameters, and spectroscopic properties of crystals of disordered scheelite-like molybdates NaLaxGd1 − x(MoO4)2 (x = 0–1) activated by Tm3+ ions

Polarized optical absorption spectra in the range of 450–2000 nm have been recorded for the Czochralski-grown concentration series of single crystals of mixed scheelite-like molybdates NaLaxGd1 − x(MoO4)2(x = 0–1) activated by Tm3+ ions. The intensity parameters Ωt (t = 2, 4, 6) of the crystals grown were determined by the Judd-Ofelt method, and the values found were used to estimate the probabilities and emission branching ratios for a number of radiative transitions of Tm3+ ions. The main optical constants of an Na0.909La0.490Gd0.498Tm0.035Mo2.020O8.048 crystal were found and the temperature dependences of the refractive index for the ordinary and extraordinary waves were investigated in the temperature range of 293–373 K. The spectral dependences of the emission cross section for the expected 3F4 → 3H6 laser transition of Tm3+ ions in an Na0.908La0.301Gd0.676Tm0.048Mo2.019O8.043 crystal were measured in the spectral range of 1500–2000 nm. The gain cross section of the active medium on the 3F4 → 3H6 laser transition of Tm3+ ions in this crystal was calculated using the spectral dependences of the absorption and emission cross sections.

Two-micron lasing on diode-pumped Y2O3 : Tm ceramics

The results of investigation of the spectral, luminescent and lasing properties of Tm : Y2O3 ceramics are presented. Lasing in Y2O3 ceramics is obtained at wavelengths of 1.95 and 2.05 μm. The maximum output laser power at these wavelengths was 2.4 and 0.3 W, respectively.

Spectroscopy of optical centers of Eu3+ ions in partially stabilized and stabilized zirconium crystals

The structure of the optical centers of Eu3+ ions in tetragonal (ZrO2)1–x–y(Y2O3)x(Eu2O3)y (х = 2.7–3.6; y = 0.1) and cubic (ZrO2)1–x–y(Y2O3)x(Eu2O3)y (х = 8–38; y = 0.1–0.5) crystals of solid solutions on the basis of zirconium dioxide is studied using the methods of optical and Raman-scattering spectroscopy. Characteristic optical centers of Eu3+ ions with different crystalline environments are revealed in the above compounds.

Structure, phase composition, and spectral-luminescent properties of ZrO2-Y2O3-Er2O3 crystals

This paper presents the results of investigations of the structure, phase composition, and spectral-luminescent properties of Er2O3-doped zirconia crystals with different Y2O3 concentrations: 99.7 mol % ZrO2-0.3 mol % Er2O3, 97.2 mol % ZrO2-1.0 mol % Y2O3-1.8 mol % Er2O3, 97.2 mol % ZrO2-2.0 mol % Y2O3-0.8 mol % Er2O3, 97.2 mol % ZrO2-2.5 mol % Y2O3-0.3 mol % Er2O3, 96.3 mol % ZrO2-3.4 mol % Y2O3-0.3 mol % Er2O3, and 86 mol % ZrO2-13.4 mol % Y2O3-0.6 mol % Er2O3. The transmission electron microscopy investigation has revealed the presence of twins in the 99.7 mol % ZrO2-0.3 mol % Er2O3 crystals with a monoclinic structure and in the 97.2 mol % ZrO2-2.5 mol % Y2O3-0.3 mol % Er2O3 and 96.3 mol % ZrO2-3.4 mol % Y2O3-0.3 mol % Er2O3 crystals with a tetragonal structure. No twins have been found in the 86 mol % ZrO2-13.4 mol % Y2O3-0.6 mol % Er2O3 crystals with a cubic structure. The phase composition of these crystals has been investigated using X-ray diffraction. It has been found that the 97.2 mol % ZrO2-1.0 mol % Y2O3-1.8 mol % Er2O3 crystals contain only the transformable tetragonal phase t, whereas the 97.2 mol % ZrO2-2.0 mol % Y2O3-0.8 mol % Er2O3, 97.2 mol % ZrO2-2.5 mol % Y2O3-0.3 mol % Er2O3, and 96.3 mol % ZrO2-3.4 mol % Y2O3-0.3 mol % Er2O3 crystals include two tetragonal phases with different degrees of tetragonality c/a: the transformable phase t and nontransformable phase t′. Specific features of the formation of Er3+ optical centers in zirconia crystals with different concentrations of stabilizing oxides have been revealed using the results of experiments on optical spectroscopy.

Phase composition and spectral-luminescent properties of yttrium partially stabilized zirconia crystals doped with Nd 2 O 3 and CeO 2

The phase composition and spectral-luminescent characteristics of yttrium partially stabilized zirconia (YSZ) crystals doped with Nd2O3 and CeO2 (ZrO2-Y2O3-Nd2O3-CeO2) are studied. X-ray diffraction shows that YSZ ZrO2-2.5 mol %Y2O3-0.2 mol %CeO2-0.1 mol %Nd2O3, ZrO2-2.03 mol %Y2O3-0.435 mol %CeO2-0.334 mol %Nd2O3, and ZrO2-2.03 mol %Y2O3-0.653 mol %CeO2-0.111 mol %Nd2O2 YSZ crystals contain two different tetragonal phases (transformable t and nontransformable ’t). The spectral-luminescent properties of these crystals indicate that Nd3+ ions occupy sites mainly in the transformable (t) phase.

Broadband white radiation in Yb3+- and Er3+-doped nanocrystalline powders of yttrium orthophosphates irradiated by 972-nm laser radiation

The up-conversion luminescence of Er3+ from the 2H11/2, 4S3/2, and 4F9/2 levels in nanocrystals of Y0.95(1‒x)Yb0.95xEr0.05PO4 (x = 0, 0.3, 0.5, 0.7, 1) orthophosphates activated with Er3+ ions has been studied under the excitation of Yb3+ ions to the 2F5/2 level by 972-nm cw laser radiation. Broadband radiation in the wavelength range of 370–900 nm has been observed at certain power densities of exciting laser radiation; this broadband radiation is absent in the case of excitation of the powders under study by pulsed laser radiation with a wavelength of 972 nm at a pulse repetition frequency of 10 Hz and a duration of a pulse of 15 ns. Experimental data indicating that this radiation is thermal in nature have been presented.

Features of the interaction of near-infrared laser radiation with Yb-doped dielectric nanoparticles

Experimental data have been presented to confirm the thermal nature of broadband visible radiation emitted from Yb3+- and Er3+-doped nanocrystalline particles of orthophosphates and orthophosphate hydrates irradiated by 972-nm near-infrared laser radiation. The mechanism of appearance of this radiation has been discussed.

Problems of High-quality Doped Y2O3-ceramics Fabrication

Tm:Y2O3, Ho:Y2O3 and Yb:Y2O3 ceramic samples were fabricated using different heat treatments modes. La2O3 (0.5 mol.%) and ZrO2 (1.5 mol.%) were used as sintering additives. Based on the investigation of structural properties of obtained samples, annealing mode was adjusted, and another set of samples with better optical quality was fabricated. In-line transmittance of the latter samples is 70% at 400nm and 75.6% at 600nm.