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The polarized absorption and emission spectra have been measured for the Tm3+ doped NaY(MoO4)2 crystal and spectral parameters have been estimated from the absorption data based on the Judd–Ofelt theory. The effective intensity parameters Ω t eff (t = 2, 4, 6) are 11.67 ×10−20, 2.21 × 10−20, 1.74 × 10−20 cm2, respectively. From the intensity parameters, the radiative transition probabilities, radiative lifetimes, branching ratios and the emission cross-section have been calculated. In comparison with other Tm3+ doped laser crystals, Tm3+:NaY(MoO4)2 crystal has potential as a promising laser crystal.

Large crystals of pure and Y b 3+ doped NaY (MoO 4 ) 2 have been grown using the Czochralski method. The major problem with these crystals is that they are black in colour, causeing total absorption in the visible range, this was resolved by annealing and the nature of the colour defect was discussed. Measurements such as DTA, thermal expansion in different crystallographic directions, and refractive index as a function of wavelength were investigated. The broad absorption band at about 980 nm and high value of the absorption cross-section are obtained for the Y b 3+ doped crystal. The results show that Y b 3+ :NaY (MoO 4 ) 2 crystal has potential as a promising laser crystal.

Good quality crystals ZnWO4 activated with Er3+ have been grown by means of Czochralski method and characterized using optical spectroscopy techniques. XRD, absorption spectra, fluorescence spectrum are presented and the Judd-Ofelt intensity parameters 522, 524, and 526 are obtained to be 6.76 x 10(-20), 0.37 x 10(-20), and 0.50 x 10(-20) cm(2), respectively. Along crystallographic axes, refractive indices are presented. The fluorescence decay time of the I-4(3/2) level has also been investigated and shows an exponential behavior with a lifetime value of 5.52 ms. The crystal is potentially used for green and infrared eye-safe lasers. (c) 2006 Elsevier B.V. All rights reserved.

The Dy3+-doped NaY(MoO4)2 single crystals were grown successfully by the Czochralski technique. The main spectroscopic properties (absorption, luminescence, decay curve) of Dy3+-doped NaY(MoO4)(2) have been determined for both the sigma and pi polarizations. By using the Judd-Ofelt theory, the measured room temperature absorption spectra were applied to determine the intensity parameters, spontaneous transition probabilities, branching ratios, and radiative lifetimes of Dy3+ transitions. The results show that the Dy3+-doped Nay(MoO4)(2) crystal may realize the yellow laser operation. (C) 2006 Elsevier B.V. All rights reserved.

Nd3+-doped NaLa(WO4)(2) single crystal with a dimension of circle divide 20 mm x 40 mm and a good optical quality was grown by Czochralski method. The polarized absorption spectra and emission spectra were measured at room temperature. The absorption cross-section and emission cross-section were presented. The Judd-Ofelt theory, extended to anisotropic system, has been applied to evaluate the intensity parameters Omega(t) (t = 2,4,6), radiative transition rates A, radiative lifetimes tau(R) and fluorescent branching ratios beta. The calculated radiative lifetime was compared with the experiment data for the F-4(3/2) emitting level. All spectral features are strongly affected by an inhomogeneous broadening connected with the 'disordered crystal' character of the title compound. (c) 2006 Elsevier B.V. All rights reserved.

NaGd(WO4)(2):Yb3+, Ho3+ single crystals have been grown by the Czochralski technique along the (0 0 1) orientation. Conversion of the infrared (IR) radiation at 980 nm into the visible emission in NaGd(WO4)(2) crystals containing several different concentrations of Yb3+ and Ho3+ has been investigated. The NaGd(WO4)(2): 8 at. % Yb3+, 4 at. % Ho3+ system exhibits intense red upconverted emission originating from the F-5(5) level. The upconversion mechanism in a Ho3+-Yb3+ system under near infrared excitation is discussed. It is concluded that the green emission is excited by energy transfers from Yb3+ to Ho3+, whereas excited state absorption is involved in the excitation of red emission. The emission cross-section of the F-5(5) -> I-5(8) transition at about 660 nm was estimated by using the Fuchtbauer-Ladengurg formula.

Holmium doped sodium gadolinium tungstate crystals with sizes of about 020 mm x 40 mm were grown successfully by the Czochralski technique along the (001) orientation. Polarized absorption spectra, fluorescence spectra and fluorescence decay curve of Ho3+-doped NaGd(WO4)(2) have been recorded at room temperature. Based on the Judd-Ofelt theory, three intensity parameters were obtained. The spectroscopic parameters of this crystal such as the oscillator strengths, radiative transition probabilities, radiative lifetimes as well as the branching ratios were calculated. The fluorescence lifetime tau(f) of the S-5(2) level was measured to be 5 mu s. (c) 2006 Elsevier B.V. All rights reserved.

Tin doped NaBi(WO4)(2) of good optical quality with sizes of about 20 min x 20 mm x 40 mm was grown successfully by the Czochralski technique. The absorption spectra for both sigma- and pi-polarizations were recorded at room temperature. Based upon these data, the oscillator strengths and radiative transition rates were evaluated. The sigma- and pi-polarized emission spectra together with the fluorescence decay curve were also obtained. The emission cross-section of the potential laser transition at 1460 nm was determined to be 1.49 x 10(-19) cm(2). The results show that Tm3+:NaBi(WO4)(2) crystal is a promising laser material. (c) 2006 Elsevier B.V. All rights reserved.

The polarized absorption, emission spectra and the fluorescence decay curve of Er3+ ions in the anisotropic NaY(MoO4)2 crystal were investigated at room temperature, and spectral parameters have been calculated from the absorption data based on the Judd–Ofelt theory. The experimental oscillator strengths for the transitions from the ground state to excited states were compared with the theoretical oscillator strengths calculated from the Judd–Ofelt theory. The emission cross-section and gain cross-section for the π- and σ-spectrum were determined for the 4H13/2 → 4H15/2 transition of special interest for laser application.

The polarized absorption and emission spectra of Pr3+ ions in NaY(MoO4)2 single crystal were investigated. The standard and modified Judd–Ofelt theory have been applied to the measured optical absorption intensities to determine the spectroscopic parameters, including the Judd–Oflet intensity parameters Ωt (t=2,4,6), the radiative transition rates, branching ratios, and emission cross-sections for various excited levels of Pr3+ ions. In samples with Pr3+ ions concentration of 2.00×1020 cm-3, the excitation of the 1D2 manifold decays non-radiatively by the electric dipole–dipole transfer between Pr3+ neighbors. The good spectroscopic properties show the possible application of the Pr3+ doped NaY(MoO4)2 crystal as a solid-state laser.

Yb3+:GdAl3(BO3)4 (hereafter Yb3+:GAB) crystals with large sizes and good optical quality have been grown by the top-seed solution growth (TSSG) method. The polarized absorption and emission spectra have been investigated at room temperature. For the σ-polarization, the intensities of both absorption and emission spectra are stronger than those for the π-polarization, the σ-absorption cross section of Yb3+ in GAB being 3.43×10-20 cm2 at 977 nm, and the σ-emission cross section being 0.98×10-20 cm2 at 1045 nm. The fluorescence lifetime of the 2 F 5/2→2 F 7/2 transition was measured to be 800 μs in the 5% doped sample used for our laser experiments, 993 μs in a 10% doped sample and 569 μs in a 0.5% doped sample. The laser parameters were estimated as: βmin=0.022, Isat=10.4 kW/cm2 and Imin=0.23 kW/cm2. About 0.4 W laseroutput at the wavelength of 1043 nm was achieved when the Yb3+:GAB crystal was pumped by a 974 nm laser diode, with 27.4% slope efficiency.

Ca3Gd2(BO3)4:Nd3+ crystals of high optical quality with a size up to 20 × 50 mm were grown by the Czochralski method. The absorption spectra of the crystal in three mutually perpendicular arbitrary directions were measured. Based on Judd–Ofelt and TPM methods, the intensity parameters Ω t (t = 2, 4, 6), the experimental and theoretical oscillator strengths, the radiative transition rates, radiative lifetime and fluorescent branching ratios of Nd3+ from 4F3/2 to 4IJ, were obtained. The fluorescence spectrum and decay curve under excitation at 808 nm were also measured. The stimulated emission cross-section and radiative quantum efficiency were also calculated.

The spectroscopic properties of GdAl3(BO3)4:Tm3+ single crystal for the Tm3+ transition near 1.9μm are presented. The absorption cross section, the emission cross section, and the potential laser gain near 1.9μm are investigated for both σ and π polarizations. The broad absorption band at about 797nm and high value of the above cross section are promising features for obtaining a laser diode pumped Tm3+ laser. The maximum emission cross sections are 1.29×10−20 and 6.60×10−20cm2 at 1.85μm for the σ and π polarizations, respectively. The potential laser gain curves indicate that more than 200nm tunability range is expected for this material.

Er3+:SrWO4 crystal of good optical quality was grown by Czochralski technique method. Polarized absorption and emission spectra of Er3+ ions in SrWO4 crystal have been investigated. The Judd-Ofelt (JO) theory was applied to the polarized absorption spectra of Er3+:SrWO4 to obtain the three JO parameters: Ω2=7.41×10−20cm2, Ω4=0.25×10−20cm2, and Ω6=1.71×10−20cm2. The radiative probabilities, radiative lifetimes, and branch ratios of Er3+:SrWO4 were calculated. The stimulated emission cross sections of the potential laser transitions at 1535nm were determined using the reciprocity method and the Fuchtbauer-Ladenberg formula, and the potential laser gain versus wavelength for the I13∕24→I15∕24 transition has been estimated and discussed.