S.D. Cheng

Enhancement of green emission from Tb3+:GdOBr phosphors with Ce3+ ion co-doping

Abstract A strong green emission (5D4→7F5) has been observed from Tb3+ (1.0 mol%) doped into GdOBr powder phosphors upon excitation with an UV-wavelength (226 nm). To this phosphor, different amounts of Ce3+ (from 0.1 to 1.5 mol%) have been added to further improve the green emission efficiency of Tb3+-doped GdOBr. It has been found that the optimum concentration, 0.2 mol% of Ce3+, results in a twofold enhancement of the green emission intensity. The green emission from Tb3+ could not be increased at higher Ce3+ concentrations due to the Ce3+-Ce3+ ion interactions, i.e., the concentration quenching effect. The mechanism involved in the energy transfer between the Ce3+ and Tb3+ has been explained with an energy level diagram.

Sol–gel derived nanocrystalline thin films of PbTiO3 on glass substrate

Thin films of PbTiO3 have been prepared on soda-lime glass substrates. The sol was prepared by mixing tetrapropyl orthotitanate and lead acetate trihydrate in acetic acid. The films were deposited by spin coating and annealed at 500°C for 30 min. The structural and optical properties of the films were characterized by means of X-ray diffraction, atomic force microscopy, variable angle spectroscopic ellipsometry, UV-VIS spectroscopy, micro-Raman spectroscopy and the m-line technique. The electrical properties of the film were studied with a Sawyer–Tower bridge. The films have a pure perovskite phase with a c/a ratio of 1.054 and consist of crystallites with a size of a few tens of nanometers. Raman studies show the typical phonon modes of PbTiO3, and the shift of the Raman peaks indicates that the films are stressed. The films are highly transparent and the absorption edge is approximately 3.70 eV. A two-layer film is found to support two TE and two TM modes at a wavelength of 633 nm.

C-axis oriented sol–gel derived LiNb1−xTaxO3 thin films on Si(111) substrates

Abstract We have successfully prepared highly c -axis oriented sol–gel derived LiNb 1− x Ta x O 3 films on Si(111) substrates. The orientations of LiNb 1− x Ta x O 3 films for different values of the tantalum composition, x , are investigated . Highly c -axis oriented films were obtained in the composition range of 0 x x c -axis orientation of the films is believed to result from a weak effect caused by the 3-fold symmetry match between the film and the Si(111) substrate. C -axis oriented LiNb 1− x Ta x O 3 films are very useful in integrated optical devices, pyroelectric devices, and metal-ferroelectric-semiconductor non-volatile memory applications.

LiTaO3 films with c-axis preferred orientation prepared on Si(111) substrate by sol-gel method

LiTaO3 films with c-axis preferred orientation have been prepared on Si(111) substrates using sol–gel spin-coating and rapid thermal annealing. Hydrogen-terminated silicon surface, preheating temperature, and unidirectional heat flow during the heat treatment are essential factors for the c-axis texture. The texture is useful in pyroelectric, metal-ferroelectric-semiconductor (MFS) nonvolatile memory, and integrated optics applications.

Up-conversion violet emission in (Nd3++Ce3+):SiO2–Al2O3 sol–gel glasses

Abstract Enhancement both in up-conversion violet emission at 399 nm ( 4 D 3/2 → 4 I 13/2 or 2 P 3/2 → 4 I 11/2 ) and in absorption strength has been observed from Nd 3+ doped SiO 2 –Al 2 O 3 sol–gel glasses after the addition of co-dopant (Ce 3+ ) ions in different contents (0.01 to 1 mol%). A very intense violet up-conversion emission was measured at an optimum Ce 3+ co-doping concentration of 0.05 mol%, when the neodymium sol–gel glass was excited with a yellow light at 577 nm( 4 I 9/2 → 4 G 5/2 ).

Fluorescence properties of Er3+;LiNbO3 sol-gel powder

Abstract This paper reports the synthesis and the upconversion green emission ( 4 S 3/2 → 4 I 15/2 ) of Er 3+ :LiNbO 3 sol–gel powder upon excitation with two NIR wavelengths (993 and 800 nm). Normal photoluminescence spectra measured at 331 and 399 nm show a bright green emission at 543 nm. Lifetimes of this green emission transition both in the upconversion and the normal emission have been compared. An NIR lasing transition ( 4 I 13/2 → 4 I 15/2 ) at 1549 nm has also been measured by pumping the sample with an Ar + laser (514 nm). Details concerning the sample structure and particles are reported here from the profiles of the X-ray diffraction (XRD) and the scanning electron microscopy (SEM) images.

Fluorescence properties of Nd3+:LiNbO3 sol–gel derived powders

Abstract Luminescence properties of Nd 3+ doped (1, 2 and 3 mol%) LiNbO 3 powders prepared by a sol–gel process are reported in this paper. Infrared emission transitions ( 4 F 3/2 → 4 I 9/2, 11/2 and 13/2 ) of Nd 3+ at 890, 1060 and 1340 nm have been measured under the excitation of an Ar + laser (514 and 488 nm) and it has been found that the 2 mol% Nd 3+ has an intense emission compared with the other contents. An up-conversion violet (398 nm) emission ( 4 D 3/2 → 4 I 13/2 or 2 P 3/2 → 4 I 11/2 ) has been observed with a 583-nm excitation, which is a hypersensitive transition ( 4 I 9/2 → 4 G 5/2 ) of Nd 3+ having a strong absorption at the yellow wavelength. Apart from a bright violet up-conversion emission, three other emissions at 342 ( 4 D 3/2 → 4 I 9/2 ), 373 ( 2 P 3/2 → 4 I 11/2 or 4 D 3/2 → 4 I 13/2 ) and 464 nm ( 2 P 3/2 → 4 I 13/2 ) have also been measured. The violet up-conversion emissions have been explained using an energy level diagram. The structural details and particle sizes of Nd 3+ -doped LiNbO 3 powders have been investigated from the XRD spectral patterns and the SEM images.

Texture developing in TiO2/ORMOSIL composite sol–gel films by ECR etching

Abstract Composite waveguide film based on TiO2/organically modified silane (ORMOSIL) has been synthesized through a sol–gel technique. Tetrapropylorthotitanate (Ti(OC3H7)4) and y-Glycidoxypropyltrimethoxysilane (GLYMO, [(CH2OCH)CH2O(CH2)3]Si(OCH3)3) were used as precursors for TiO2/ORMOSIL composite films. Chain-like texture structure in the electron cyclotron resonance (ECR)-etched composite waveguide film was observed during the fabrication of optical channel waveguides. The morphology and structure were characterized by using scanning electron microscopy (SEM) and Fourier transforms infrared spectroscopy (FTIR). It is proposed that the formation of the texture structure be due to the induced polymerization of the GLYMO monomer in the presence of plasma or gas catalyst.

Structural, electrical, and optical properties of sol-gel-processed thin films of BaTiO3 on ITO glass

BaTiO3 thin films are prepared on ITO-coated Corning 1737 glass. The solution is prepared from a double metal ethoxide and the films are deposited by spin coating and annealing at 700°C for 2 hours in an O2 atmosphere. The films are characterized using x-ray diffraction, atomic force microscopy, micro-raman, UV-VIS spectroscopy, and Sawyer-Tower Bridge. The pure perovskite phase of BaTiO3 is identified by x-ray diffraction. The tetragonality is revealed from Raman study by identifying the symmetrical dependent Raman shift at about 306 cm-1. The ferroelectricity of the film is confirmed by the P-E hysteresis loop. The films are highly transparent, with an absorption edge at 3.73eV. These desirable features indicate that the films have potential in electronic display and electro-optical applications.

Ferroelectric properties of SOL-GEL derived thin solid film of barium titanate on ITO-glass

Abstract Ferroelectric thin films of BaTiO3 were prepared by a sol-gel technique on ITO-glass substrates and annealed at 650°C for 30 seconds in a rapid thermal processor (RTP) with O2atmosphere. X-ray diffraction (XRD), atomic force microscopy (AFM) and transmission spectroscopy were used to study the surface morphology and the microstructure of the films, and the results showed that the films were well crystallized, crack-free, smooth, and highly transparent in the visible-near infrared spectral zone. The ferroelectric properties of the films have been studied. A butterfly C-V loop was observed and a remnant polarization of P r=6.3 μ C/cm2 and a coercive field of Ec =8.4 kV/cm were determined from the ferroelectric hysteresis loop.