Growth and spectroscopic characteristics of Yb : GSO single crystal

For the first time, a high optical quality 10 at.% Yb3+-doped gadolinium oxyorthosilicate laser crystal Gd2SiO5 (GSO) was grown by the Czochralski (Cz) method. The segregation coefficient of Yb3+ was studied by the inductively coupled plasma atomic emission spectrometer (ICP-AES) method. The crystal structure has monoclinic symmetry with space group P2(1)/c; this was determined by means of an x-ray diffraction analysis. The absorption spectra, fluorescence spectra and fluorescence decay curves of Yb3+ ions in a GSO crystal at room temperature were also studied. Then, the spectroscopic parameters of Yb:GSO were calculated. The advantages of the Yb:GSO crystal include high crystal quality, quasi-four-level laser operating scheme, high absorption cross-sections and particularly broad emission bandwidth (similar to 72 nm). The results indicated that the Yb:GSO crystal seemed to be a very promising laser gain medium in diode-pumped femtosecond laser and tunable solid state laser applications when LD pumped at 940 and 980 nm.

Structural and optical properties of YAG : Ce3+ phosphors by sol-gel combustion method

High-quality Ce3+-doped Y3Al5O12 (YAG:Ce3+) phosphors were synthesized by a facile sol-gel combustion method. In this sol-gel combustion process, citric acid acts as a fuel for combustion, traps the constituent cations and reduces the diffusion length of the precursors. The XRD and FT-IR results show that YAG phase can form through sintering at 900 degrees C for 2 h. This temperature is much lower than that required to synthesize YAG phase via the solid-state reaction method. There were no intermediate phases such as YAlO3 (YAP) and Y4Al2O9 (YAM) observed in the sintering process. The average grain size of the phosphors sintered at 900-1100 degrees C is about 40 nm. With the increasing of sintering temperature, the emission intensity increases due to the improved crystalline and homogeneous distribution of Ce3+ ions. A blue shift has been observed in the Ce3+ emission spectrum of YAG:Ce3+ phosphors with increasing sintering temperatures from 900 to 1200 degrees C. It can be explained that the decrease of lattice constant affects the crystal field around Ce3+ ions. The emission intensity of 0.06Ce-doped YAG phosphors is much higher than that of the 0.04Ce and 0.02Ce ones. The red-shift at higher Ce3+ concentrations may be Ce-Ce interactions or variations in the unit cell parameters between YAG:Ce3+ and YAG. It can be concluded that the sol-gel combustion synthesis method provides a good distribution of Ce3+ activators at the molecular level in YAG matrix. (c) 2005 Elsevier B.V. All rights reserved.

Three-photon-excited upconversion luminescence of Ce3+: YAP crystal by femtosecond laser irradiation

Infrared to ultraviolet and visible upconversion luminescence was demonstrated in trivalent cerium doped YAlO3 crystal (Ce3+: YAP) under focused infrared femtosecond laser irradiation. The fluorescence spectra show that the upconverted luminescence comes from the 5d-4f transitions of trivalent cerium ions. The dependence of luminescence intensity of trivalent cerium on infrared pumping power reveals that the conversion of infrared radiation is dominated by three-photon excitation process. It is suggested that the simultaneous absorption of three infrared photons pumps the Ce3+ ion into upper 5d level, which quickly nonradiatively relax to lowest 5d level. Thereafter, the ions radiatively return to the ground states, leading to the characteristic emission of Ce3+. (c) 2005 Optical Society of America.

gamma-LiAlO2 single crystal grown by Czochralski technique and modified by vapor transport equilibration (VTE) technique

Large-sized (similar to 2 inch, 50.8 mm) gamma-UA102 single crystal has been grown by conventional Czochralski (Cz) method, but the crystal ha's a milky, dendriform center. The samples taken from transparent and milky parts were ground and examined by X-ray diffraction. All diffraction peaks could be indexed in gamma-LiAlO2. The crystal quality was characterized by X-ray rocking curve. The full-width at half-maximum (FWHM) values are 116.9 and 132.0 arcsec for transparent and milky parts, respectively. The vapor transport equilibrium (VTE) technique was introduced to modify the crystal quality. After 1000 degrees C/48 h, 1100 degrees C/48 h, 1200 degrees C/48 h VTE processes, the FWHM values dropped to 44.2 and 55.2 arcsec for transparent and milky part, respectively. The optical transmission of transparent part was greatly enhanced from 85% to 90%, and transmission of milky part from 75% to 80% in the range of 190 similar to 1900 nm at room temperature. When the VTE temperature was raised to 1300 degrees C, the sample cracked and FWHM values of transparent and milky parts were increased to 55.2 and 80.9 arcsec, respectively. By combining Cz technique with VTE technique, large-sized and high quality gamma-LiAlO2 crystal can be obtained.

Czochralski growth and crystal structure of cerium-doped Lu2Si2O7 scintillator

Cerium-doped lutetium pyrosilicate crystal, Ce:Lu2Si2O7 (Ce:LPS), was grown by the Czochralski method. The segregation coefficient of Ce3+ ion was studied by the ICP-AES method. X-ray diffraction analysis showed that the structure of Ce:LPS crystal was monoclinic symmetry with space group of C2/m. Perfect cleavage planes (110) and imperfect cleavage planes (001) were observed by optical microscope. The reasons why it is difficult to grow crack-free crystals were studied. After optimized growth parameters, a Ce:LPS crystal with dimension of Phi 25 x 30 mm was grown, which is colorless, high optical quality, cracking-free and no inclusions. The transmittance of Ce:LPS crystal from 380 to 800 nm is over 82% and there is no observable absorption. (c) 2005 Elsevier B.V. All rights reserved.

Defect analysis in Czochralski-grown Yb : FAP crystal

Growth-induced defects in Yb:FAP crystals grown by the Czochralski method have been investigated by optical microscopy, chemical etching, scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). Anisotropic etching features have been observed on two FAP crystal planes: (0001) and (1010). The shape of etch pits on the (0001) plane is hexagonal, while the etch pits on the (1010) plane have a variety of irregular shapes. It is also found that the density of etch pit varies along the boule. Based on the experimental observations, the formation mechanisnis of growth defects are discussed, and methods for reducing the growth-induced defect concentration is proposed. (c) 2005 Elsevier B.V. All rights reserved.

Structural, optical and electrical properties of ZnO films grown on c-plane sapphire and (100)gamma-LiAlO2 by pulse laser deposition

ZnO thin films were grown on single-crystal gamma-LiAlO2 (LAO) and sapphire (0001) substrate by pulsed laser deposition (PLD). The structural, optical and electrical properties of ZnO films were investigated. The results show that LAO is more suitable for fabricating ZnO films than sapphire substrate and the highest-quality ZnO film was attained on LAO at the substrate temperature of 550 degrees C. However, when the substrate temperature rises to 700 degrees C, lithium would diffuse from the substrate (LAO) into ZnO film which makes ZnO film on LAO becomes polycrystalline without preferred orientation, the stress in ZnO film increases dominantly and the resistivity of the film decreases exponentially. (c) 2005 Elsevier B.V. All rights reserved.

Ti:sapphire laser pumped high average power laser crystal Nd:GGG with high efficiency output

High-quality neodymium doped GGG laser crystals have been grown by Czochralski (Cz) method. Results of Nd:GGG thin chip laser operating at 1.064 μm pumped by Ti:sapphire laser operating at 808 nm were reported. The slop efficiency was as high as 20%.

Influence of vapor transport equilibration on the crystal quality and thermal-expansion coefficients of gamma-LiAlO2

gamma-LiAlO2 (LAO) single crystal has been grown by the Czochralski method. However, its quality was deteriorated due to lithium volatilization during the crystal growth. The full width at half maximum value drops from 116.9 to 44.2 arc sec after the LAO slice was treated by vapor transport equilibration at 1000, 1100, and 1200 degrees C/48 h in sequence. The treated slice shows higher optical transmission than the as-grown one in the measured wavelength range of 190-1900 nm, meanwhile, its absorption edge exhibits a blueshift. According to Raman spectra, the treated slice has homogeneous quality at different depths from surface to 0.01 mm. The expansion coefficient of the treated slice for a axis drops from 17.2398x10(-6)/degrees C to 16.5240x10(-6)/degrees C, and that for c axis drops from 10.7664x10(-6)/degrees C to 10.0786x10(-6)/degrees C.

Spectral properties and charge transfer luminescence of Yb3+ : Gd3Ga5O12 (Yb : GGG) crystal

The Yb (10%):GGG and Yb (30%): GGG crystals have been grown by the Czochralski method. The chemical compositions are: Yb1.07Gd1.74Ga5.19O12 and Yb0.33Gd1.47Ga5.2O12. The absorption and emission spectra of Yb:GGG crystal at room temperature have been measured. The spectroscopic parameters of Yb:GGG and Yb:YAG have been compared. Optical absorption spectra of Yb:GGG show 4f-4f transitions related to Gd3+ ion around 300 nm, and also an onset of charge transfer (CT) transitions from oxygen ligands to Gd3+ or Yb3+ cations below 240nm. The CT absorption of Yb3+ is largely overlapped by that of Gd3+ ions. (c) 2005 Elsevier B.V. All rights reserved.

Spectral hole-burning of Eu3+: Y2SiO5 crystal at 579.62 mm

By using an Ar+ ion laser, a tunable Rh 6G dye laser(Linewidth : 0.5 cm(-1)) and a Coherent 899-21 dye laser as light sources and using a monochromator and a phase-locking amplifier, the optical properties of Eu3+ : Y2SiO5 crystal were detected. Persistent spectral hole burning (PSHB) were also observed in (5)Do-(7)Fo transition in the crystal at the temperature of 16 K. For 15 mW dye laser (Wavelength : 579.62 nm) burning the crystal for 0.1 s a spectral hole with about 80 MHz hole width were detected and the hole can been keep for longer than 10 h.

Spectral properties of Ho : GdVO4 single crystal

Absorption and emission spectral properties of GdVO4 single crystal doped with Ho3+ ions were investigated at room temperature. Polarized absorption cross section is calculated in the range of 400-2200nm. Results were analyzed and parameters were calculated based on Judd-Ofelt theory, the emission spectrum shows that the emission intensity around the wavelength of 546 nm associated with transition S-5(2) -> I-5(8) is much stronger than other bands in the observed range and potentially enable the green light output around this emission band in this crystal. (c) 2006 Elsevier B.V. All rights reserved.

Diode-pumped passively q-switched Nd : YAG ceramic laser with a Cr4+: YAG crystal-satiable absorber

Transparent polycrystalline Nd:YAG ceramics were fabricated by solid-state reactive sintering a mixture of commercial Al2O3,Y2O3, and Nd2O3 powders. The powders were mixed in ethanol and doped with 0.5 wt% tetraethoxysilane, dried, and pressed. Pressed samples were sintered at 1750 degrees C in vacuum. Transparent fully dense samples with average grain sizes of 10 mu m were obtained. The 1 at.% Nd:YAG ceramic was used to research passively Q-switched laser output with a Cr4+:YAG crystal as a saturable absorber. An average output power of 94 mW with a pulse width of 50 ns was obtained when the incident pump power was 750 mW. The slope efficiency was 13%. The pulse energy is 5 mu J, and the peak power is about 100 W.

Growth and spectroscopic characteristics of Yb : LPS single crystal

For the first time, a high optical quality Yb3+-doped lutetium pyrosilicate laser crystal Lu2Si2O7 (LPS) was grown by the Czochralski (Cz) method. The segregation coefficient of ytterbium ion in Yb:LPS crystal detected by the inductively coupled plasma atomic emission spectrometer (TCP-AES) method is equal to 0.847. X-ray powder diffraction result confirms the C2/m phase monoclinic space group of the grown crystal and the peaks corresponding to different phases were indexed. The absorption and fluorescence spectra, as well as fluorescence decay lifetime of Yb3+ ion in LPS have been investigated. The absorption and fluorescence cross-sections of the transitions F-2(7/2) <-> F-2(5/2) of Yb3+ ion in LPS crystal have been determined. The advantages of the Yb:LPS crystal including high crystal quality, quasi-four-level laser operating scheme, high absorption cross-sections (1.33 x 10(-2) cm(2)) and particularly broad emission bandwidth (similar to 62 nm) indicated that the Yb:LPS crystal seemed to be a promising candidate used as compact, efficient thin chip lasers when LD is pumped at 940 and 980 nm due to its low-symmetry monoclinic structure and single crystallographic site. (c) 2007 Elsevier B.V. All rights reserved.

Spectroscopic properties of Ce : YAP scintillation crystal grown by temperature gradient technique

Spectroscopic properties of Ce-doped yttrium orthoaluminate (Ce:YAlO3 or Ce:YAP) crystals grown by temperature gradient technique (TGT) were investigated, and the effects of the growth conditions on the properties were analyzed.. Methods of optical absorption (OA), photoluminescence (PL), photoluminescence decay (PLD), X-ray excited luminescence (XL) and cathodeluminescence (CL) were used in these investigations. The results showed that the absorption band peak at 202, 394 and 532 nm originated from F and F+ color center induced by the weak reducing growth atmosphere, green emission band near 500 ran derived from Ce3+ -Ce3+ pairs and band at 650 similar to 850 run from some unintentional impurity in crystals.