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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.

The single crystal of ZnWO 4 :Ho 3+ was grown by Czochralski technique. The XRD, absorption spectra, fluorescence spectrum are presented, and the Judd–Ofelt (J–O) intensity parameters Ω 2 , Ω 4 , Ω 6 are obtained to be 4.61 × 10 −20 cm 2 , 0.16 × 10 −20 cm 2 , 0.48 × 10 −20 cm 2 , respectively. Calculated radiative transition rate, branching ratios, and radiative lifetime for different transition levels of ZnWO 4 :Ho 3+ crystals are presented. The most intense line correlative with the transition 5 S 2 → 5 I 8 at 543 nm is potentially used for green solid state laser, and the fluorescence lifetime of this energy level is 14.1 μs.

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.

Dy3+-doped NaGd(WO4)(2) crystal with sizes of about Phi 20x40 mm(2) was grown by the Czochralski technique along the (001) orientation. Polarized absorption spectra, fluorescence spectra, and fluorescence decay curve of Dy3+-doped NaGd(WO4)(2) have been recorded at room temperature. Based on the Judd-Ofelt (J-O) theory, the intensity parameters from the measured line strengths were evaluated. The J-O parameters were used to predict radiative transition probabilities, radiative lifetimes and branching ratios for various excited levels of Dy3+-doped NaGd(WO4)(2) crystal. The luminescent quantum efficiency of the F-4(9/2) level was determined to be approximately 63% for this material. The emission cross-section of the F-4(9/2)-> H-6(13/2) transition was estimated by using the Fuchtbauer-Ladengurg method. (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.

Single-crystal ZnWO4:Dy3+ was grown by Czochralski technique. The XRD, absorption spectra as well as fluorescence spectrum are investigated and the Judd-Ofelt intensity parameters Omega(2), Omega(4), Omega(6) are obtained to be 7.76 x 10(-20) cm(2), 0.57 x 10(-20) cm(2), 0.31 x 10(-20) cm(2), respectively. Calculated radiative transition rate, branching ratios and radiative lifetime for different transition levels of ZnWO4:Dy3+ crystals are presented. Fluorescence lifetime of F-4(9/2) level is 158 mu s and quantum efficiency is 66%. The most intense fluorescence line at 575 nm correlative with transition F-4(9/2) -> H-6(13/2) is potentially for application of yellow lasers. (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.

NaLa(WO4)(2):Dy3+ crystals were grown successfully by the Czochraski technique. The Raman, infrared, electronic absorption and emission spectra were measured at room temperature. 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. Although there are several transitions originating in the F-4(9/2) level, a major part of emission intensity is contained in the F-4(9/2) -> 6H(13/2) transition. The stimulated emission cross-sections for this transition were estimated by using the Fochtbauer-Ladenburg method. The luminescence decay curve was also measured at room temperature. The results indicate that NaLa(WO4)(2):Dy3+ may be considered as laser active materials operating near 0.57 mu m. (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.

Tm 3 + : Ba 3 Gd 2 ( BO 3 ) 4 crystal with the size up to Φ 13 mm×44 mm was grown successfully by the Czochralski technique and its optical properties were presented. The absorption cross-section and emission cross-section were presented. Also, the potential laser gain near 1.9 μm was investigated. In the framework of the Judd–Ofelt (J–O) theory, the intensity parameters were calculated to be: Ω2=11.375×10−20 cm2, Ω4=5.077×10−20 cm2 and Ω6=6.524×10−20 cm2. The spectroscopic parameters of this crystal such as the oscillator strengths, radiative transition probabilities, radiative lifetime as well as the branching ratios were calculated, too. This crystal is promising as a tunable infrared laser crystal.

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.

A systematic investigation of room temperature absorption and emission spectra were presented for trivalent holmium in a crystal of NaY(MoO4)2. Oscillator strengths of the transitions to all levels up to 361 nm were calculated from the absorption spectra. Judd–Ofelt intensity parameters of Ho3+ were used to calculate the radiative transition rates, branching ratios and radiative lifetimes. The emission cross-sections for the 5S2 → 5I8 and 5I7 → 5I8 transitions of special interest for laser application were determined.

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.

The 1D photonic crystals based on multilayer porous silicon are reported in this paper. The photonic structures are composed of alternating high and low dielectric function porous silicon layers by changing the porosity of porous silicon with a periodic electric pulse alternating between 10.0 and 70.0 mA/cm2 during anodization on p+-type (1 0 0) silicon wafer with resistance range 0.01–0.02 Ω cm. Omni-directional mirrors as well as narrow band filters working in the range around 1.55 μm are designed and fabricated. Photonic crystal with such a structure exhibits high quality of filter behavior.

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.

Thulium doped sodium gadolinium tungstate crystals with sizes of about 20 mm×45 mm were grown successfully by the Czochralski technique along the (001) orientation. X-ray powder diffraction (XRD) of sodium gadolinium tungstate was described and the linear thermal expansion coefficients for the c- and a-axes were measured as 1.60×10-5 and 7.89×10-6 °C-1. Polarized absorption spectra, and fluorescence spectra, as well as fluorescence decay curves of Tm3+-doped NaGd(WO4)2, have been recorded at room temperature and used to calculate the absorption and stimulated emission cross-sections. Based on the Judd–Ofelt theory, three intensity parameters were obtained. The luminescent quantum efficiency of the 3 H 4 level was determined to be approximately 65% for this material. The emission cross-section of the 3 F 4→3 H 6 IR transition at about 1.8 μm was estimated by the reciprocity method.

Ca3(BO3)2 single crystals have been grown by the Czochraski technique. The absorption and emission spectra have been measured at room temperature. From the Judd–Ofelt theory analysis, the intensity parameters were determined to be Ω2 = 4.63 × 10–20 cm2, Ω4 = 2.40 × 10–20 cm2, and Ω6 = 10.4 × 10–20 cm2. The calculated radiative probabilities, radiative lifetimes, and the branching ratios have been evaluated for the 4F3/2 excited state using the calculated intensity parameters. The stimulated emission cross-section was also measured at 1060 nm. The results indicate that this crystal can be considered as a promising material for solid-state laser application. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

This paper reports the growth of Nd3+:NY(WO4)2 crystal with high optical quality and large size. Nd3+:NY(WO4)2 crystal with the dimension Φ30×75 mm2 and optical homogeneity 4×10−5 was grown by Czhchoralski method: the seed used was [1 0 0] orientation, the pulling rate and rotating rate were 0.5–1.25 mm/h and 15 rpm, respectively. The growing processes and characteristics of Nd3+:NY(WO4)2 crystal was discussed. Its unpolarized absorption spectra and emission spectra were measured. The absorption cross-section and emission cross-section were presented. Based on the Judd–Ofelt theory, we obtained the three intensity parameters: Ω 2 = 5.8 × 1 0 - 20 , Ω 4 = 5.74 × 1 0 - 20 , and Ω 6 = 4.32 × 1 0 - 20 cm 2 . The radiative probabilities, radiative lifetimes, branch ratios and quantum efficiency of Nd3+:NY(WO4)2 were calculated too.

Dy 3+ : Ca 3 (BO 3 ) 2 crystal was grown successfully by the Czochraski technique. The absorption spectrum was measured and its absorption peaks were assigned. The Judd–Ofelt intensity parameters were found to be Ω 2 =5.216×10 −20 , Ω 4 =1.858×10 −20 , Ω 6 =0.623×10 −20 cm 2 . The spectroscopic parameters of this crystal such as the oscillator strengths, radiative transition probabilities, radiative lifetime as well as the branching ratios were calculated. Also, room temperature luminescence decay curve in correspondence with the emission line 4 F 9/2 → 6 H 13/2 centered at 575 nm was measured.

Large novel birefringent pure and rare earth-doped calcium borate crystals (Ca 3 (BO 3 ) 2 ) have been grown successfully by Czochralski technique. Thermal expansion coefficients of pure Ca 3 (BO 3 ) 2 have been obtained for the first time. Trivalent rare earth ions (RE 3+ ), such as Dy 3+ - and Nd 3+ -doped calcium borate crystal, have been grown for optic application. Absorption and fluorescence spectra as well as fluorescence decay curves of Dy 3+ -, Nd 3+ -doped Ca 3 (BO 3 ) 2 crystals are measured at room temperature. Optical spectra show that there are obvious absorptions at ultraviolet to IR region. The strong emissions in visible and infrared region show that calcium borate is a suitable for rare earth-doped laser crystal.

The crystal of ZnWO4 doped with Co2+ has been grown by the Czochralski technique. The orientation procedure was presented. Along the crystallographic axes, the principal coefficients of thermal expansion and absorption spectra were measured and discussed. Based on the data, the crystal field parameter 10Dq, Racah parameter B, as well as the absorption cross sections were calculated. The nonlinear dependence of optical absorption on concentration of cobalt ions was found and discussed in single crystal Co2+:ZnWO4. The results indicate that inner defects such as natural cleavage or slip faces in crystal are important in the study of optical and thermal properties.

The polarized absorption, emission spectra, and the fluorescence decay curve of Er3+ ions in the anisotropic Ca3(BO3)2 crystal were investigated at room temperature. The experimental oscillator strengths for the transitions from the ground state to excited states were compared with the theoretical electric dipole oscillator strengths calculated from the Judd-Ofelt [Phys. Rev. 127, 750 (1962); J. Chem. Phys. 37, 511 (1962)] theory. The emission cross sections and gain cross sections of the π and σ spectra were determined for the H13∕24→H15∕24 transition of special interest for laser application.

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.