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The spectroscopic properties of Ho3+ laser channels in locally disordered tetragonal NaBi(WO4)2 (NaBiW), NaBi(MoO4)2 (NaBiMo), and LiBi(MoO4)2 (LiBiMo) single crystals grown by the Czochralski method have been studied in the 5-300-K temperature range using several holmium concentrations [Ho]approximate to 0.05-0.6x10(20) cm(-3). Here 5-K polarized optical absorption and photoluminescence measurements have been used to determine the energy position of 85, 56, and 39 Ho3+ Stark levels in NaBiW, NaBiMo, and LiBiMo crystals, respectively. These energy levels were labeled with irreducible representations corresponding to the S-4 local symmetry of an average optical center. Single-electron Hamiltonians combining together free-ion and crystal-field interactions have been used in the fit of experimental energy levels and in the simulation of the corresponding 4f(10) Ho3+ configuration for NaBiW and NaBiMo crystals. Very satisfactory correlations were obtained between experimental and calculated crystal-field levels, with rms deviations sigma=8.8 and 7.3 cm(-1) for NaBiW and NaBiMo, respectively. The radiative properties and emission cross sections of Ho3+ laser channels in these hosts were calculated by the Judd-Ofelt theory and compared with experimental results. The emission cross sections of Ho3+ in NaBiW are similar to those observed in other crystal laser hosts, and positive gain cross sections can be achieved in extended spectral ranges. These properties make the Ho3+-doped double tungstates and double molybdates feasible materials for tunable and short-pulse laser operation., This work was financed by the European Union through the DT-CRYS or NMP3-CT-2003-505580 project and by Spain through the MAT2002-04603-C05-05 (also EU FEDER found) and MAT2005-06354-C03-01 projects. A.M.B. was supported by CONACyT (México) Grant No. 128118. M.R. is supported by the Spanish Education Ministry under the “Ramón y Cajal” program.

Filing Date: 2004-07-14.-- Priority Data: ES 200301666 (2003-07-15).-- International Publication Number: WO_2005008175 (20050127)., This invention is related to the production engineering industry, and more particularly to the sector concerned with the production of photovoltaic cells, and therefore it also has a bearing on the alternative energy sector. The invention relates to the control of the methods used for texturing the surface of monocrystalline silicon, although it is also applicable to the textures developed on the surface of silicon and other multicrystalline and polycrystalline semiconductors.

La Ciencia de los Materiales es una ciencia nueva aceptada cómo disciplina científica en 1958. El desarrollo científico y tecnológico de la segunda mitad del siglo XX no hubiera sido posible sin el desarrollo de materiales, algunos de ellos desconocidos con anterioridad. Actualmente la Ciencia de Materiales es una ciencia multidisciplinar y el futuro necesita desarrollar tecnologías sostenibles de producción y consumo de energía que requieren, entre otras cosas, nuevos materiales hoy inexistentes con nuevas propiedades más sofisticadas.

Single crystals of Yb3+-doped NaGd(WO4)2 with up to 20 mol % ytterbium content have been grown by the Czochralski technique in air or in N-2+O-2 atmosphere and cooled to room temperature at different rates (4-250 degrees C/h). Only the noncentrosymmetric tetragonal space group I-4 accounts for all reflections observed in the single crystal x-ray diffraction analysis. The distortion of this symmetry with respect to the centrosymmetric tetragonal space group I4(1)/a is much lower for crystals cooled at a fast rate. Na+, Gd3+, and Yb3+ ions share the two nonequivalent 2b and 2d sites of the I-4 structure, but Yb3+ (and Gd3+) ions are found preferentially in the 2b site. Optical spectroscopy at low (5 K) temperature provides additional evidence of the existence of these two sites contributing to the line broadening. The comparison with the F-2(7/2)(n) and F-2(5/2)(n(')) Stark energy levels calculated using the crystallographic Yb-O bond distances allows to correlate the experimental optical bands with the 2b and 2d sites. As a novel uniaxial laser host for Yb3+, NaGd(WO4)2 is characterized also with respect to its transparency, band-edge, refractive indices, and main optical phonons. Continuous-wave Yb3+-laser operation is studied at room temperature both under Ti:sapphire and diode laser pumping. A maximum slope efficiency of 77% with respect to the absorbed power is achieved for the pi polarization by Ti:sapphire laser pumping in a three-mirror cavity with Brewster geometry. The emission is tunable in the 1014-1079 nm spectral range with an intracavity Lyot filter. Passive mode locking of this laser produces 120 fs long pulses at 1037.5 nm with an average power of 360 mW at approximate to 97 MHz repetition rate. Using uncoated samples of Yb:NaGd(WO4)2 at normal incidence in simple two-mirror cavities, output powers as high as 1.45 W and slope efficiencies as high as 51% are achieved with different diode laser pump sources., Projects DT-CRYS or NMP3-CT-2003-505580 (EU), MAT2005-6354-C03-01 (Spain), and BMBF 13N8382 (Germany). M.R. thanks the Education and Science Ministry of Spain for financial support (EX2003-0784).

The spectroscopic properties of Ho3+ laser channels in KGd(WO4)2 crystals have been investigated using optical absorption, photoluminescence, and lifetime measurements. The radiative lifetimes of Ho3+ have been calculated through a Judd-Ofelt (JO) formalism using 300-K optical absorption results. The JO parameters obtained were Ω2=15.35×10-20 cm2, Ω 4=3.79×10-20 cm2, Ω6 =1.69×10-20 cm2. The 7-300-K lifetimes obtained in diluted (8·1018 cm-3) KGW:0.1% Ho samples are: τ(5F3)=0.9 μs, τ( 5S2)=19-3.6 μs, and τ(5F5 )=1.1 μs. For Ho concentrations below 1.5×1020 cm-3, multiphonon emission is the main source of non radiative losses, and the temperature independent multiphonon probability in KGW is found to follow the energy gap law τph -1(0)=βexp(-αΔE), where β=1.4×10-7 s-1, and α=1.4×103 cm. Above this holmium concentration, energy transfer between Ho impurities also contributes to the losses. The spectral distributions of the Ho3+ emission cross section σEM for several laser channels are calculated in σ- and π-polarized configurations. The peak a σEM values achieved for transitions to the 5I8 level are ≈2×10-20 cm2 in the σ-polarized configuration, and three main lasing peaks at 2.02, 2.05, and 2.07 μm are envisaged inside the 5I7→5I8 channel., This work was supported by Comisión Interministerial de Ciencia y Tecnología under Projects MAT99-1077 and 2FD97-0912.

[ES] Se ha estudiado el proceso de depósito mediante ablación con láser de láminas delgadas de PbTiO3 modificado con La (PLT) y ZnO sobre (100)InP. Para el PLT se han depositado láminas intermedias de óxidos dieléctricos (CeO2, ZrO2, SrO, YSZ, MgO, y SrTiO3) necesarias para la protección de la superficie del substrato. En cada caso se han establecido las condiciones experimentales (presión de oxígeno, temperatura del substrato, densidad de energía del pulso láser y limpieza de la superficie del substrato) necesarias para obtener láminas cristalinas con orientación preferente. En la heteroestructura PLT/YSZ/(100)InP se estudian los cambios de composición y morfología a lo largo del perfil de la heteroestructura, a fin de investigar los procesos involucrados en el crecimiento de estos óxidos sobre el (100)InP., [EN] The oriented growth of PbLaTiO3 (PLT) and ZnO thin films on (100)InP has been studied, including the influence of buffer oxide layers (CeO2, ZrO2, SrO, YSZ, MgO, and SrTiO3) on the final texture of PLT film obtained. In each case the oxygen pressure, substrate temperature, energy fluence and substrate surface conditions required to obtain a crystalline and preferentially oriented phase have been established. The composition and morphological changes related to the PLT/YSZ/(100)InP heterostructure profile have been studied in order to investigate the processes involved in the growth of these oxides on (100)InP., Este trabajo ha sido financiado por CICyT y por la Comunidad Autónoma de Madrid con de los proyectos TIC96- 1039 y 07T/0032/1997 respectivamente. E. V. está subvencionado por la Agencia Española de Cooperación Internacional a través de una beca doctoral Mutis.

[ES] La técnica de depósito mediante ablación con láser es particularmente adecuada para la formación de láminas delgadas de óxidos con varios cationes, por ello se ha aplicado a la preparación de óxidos superconductores, ferroeléctricos y electroópticos. En este trabajo se señalan las ventajas de la técnica y simultáneamente se enfatizan algunos mecanismos secundarios que conducen a diferencias en la composición entre el blanco y la lámina. Específicamente se comentan las modificaciones del blanco, los procesos de dispersión en la fase vapor, la interdifusión entre la lámina y el substrato y la evaporación de especies de la lámina. Estos fenómenos se ilustran mediente el depósito de óxidos de niobio y titanatos de plomo. La compresión de los mecanismos relevantes para cada material permite optimizar las condiciones depósito hasta obtener láminas con la composición y cristalinidad para algunas aplicaciones microeléctricas y ópticas., [EN] Pulsed laser deposition technique is very well suited for thin film preparation of multicomponent oxides. It has been applied to the deposition of superconductor, ferroelectric and electrooptics oxides. The main advantages of the technique are briefly summarised in this review, moreover some physical mechanisms leading to a film composition departure from the target one are analysed. Particular attention is paid on the laser-induced modification of the target, scattering in the plume, film diffusion into the substrate and reevaporation from the film. These phenomena are illustrated with niobate and lead titanate oxides. The proper understanding of these phenomena allows the optimisation of the deposition parameters to achieve specific crystalline films suited for some microelectronics and optical applications., Este trabajo se ha desarrollado bajo financiación de la CICyT a través del proyecto TIC96-1039.