X. Q. Han

Green upconversion luminescence in Er3+:BaTiO3 films

Green upconversion emissions at 548 and 528 nm have been obtained from sol-gel derived nanocrystalline Er3+:BaTiO3 films under 980 nm excitation. The green emissions are attributed to the ground-state (4I15/2) -directed transitions from 2H11/2 (528 nm) and 4S3/2 (548 nm) of Er3+ ions. Analysis of the temporal evolution of the emission at 548 nm shows that both excited state absorption of individual ion and energy transfer between the two neighboring ions contribute to the upconversion emissions in Er3+ (3 mol %):BaTiO3 film. The lifetime of the dominant emission at 548 nm is about 90 μs.

Visible up-conversion luminescence in Er3+:BaTiO3 nanocrystals

Abstract Visible emissions at 548, 528 and 660 nm have been observed from the sol–gel derived nanocrystalline Er 3+ :BaTiO 3 powders under infrared excitations at both 980 and 810 nm. Combined with the energy level structure of Er 3+ and the decay kinetics of the green emissions, the up-conversion mechanism has been analyzed and explained. The bright green emission at 548 nm has been attributed to the ground state-directed transition from 4 S 3/2 , which is populated through excited state absorption (ESA) for 810 nm excitation, and through both ESA and energy transfer (ET) processes for 980 nm excitation.

Deposition and photoluminescence of sol-gel derived Tb3+:Zn2SiO4 films on SiO2/Si

Abstract Tb3+ doped Zn2SiO4 films have been deposited on SiO2 buffered Si wafers by sol–gel method. The structures of these films have been investigated with X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The results revealed that these films were composed of nanometer-size grains with a Willemite structure and had smooth surfaces. Photoluminescence measurements of the films showed a strong emission from 5D4 to 7F5 at 544 nm. The blue emission from 5D3–7Fj was depressed because of cross-relaxation effect. The decay kinetics of the 5D4–7F5 green emission was studied and a best fitting was obtained by a double exponential function. The lifetime of the excited 5D4 state is estimated to be 5.2 ms.

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.

Photoluminescence at 1.54 μm in sol-gel-derived, Er-doped BaTiO3 films

Abstract Nanostructured Er-doped BaTiO 3 films were deposited by the sol-gel method on SiO 2 /Si substrates. The spontaneous luminescence in the films at 1.54 μm was observed under the excitation of both 514 and 980 nm lasers. Transient photoluminescence showed that, for the Er:BaTiO 3 film containing 3.0 mol% Er, the decay of the 1.54 μm emission is a single exponential decay with a 1/ e lifetime of ∼5 ms. Concentration quenching was observed for the film containing 5.0 mol% Er, which was attributed to energy transfer and cross relaxation between closely sited Er 3+ ions in the BaTiO 3 lattice.

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.

Deposition of potassium lithium niobate films by sol-gel method

Potassium lithium niobate (KLN) films have been prepared by sol-gel method using metal ethoxides as starting materials. The films were deposited by spin coating and were annealed in air in a conventional oven as well as in a rapid thermal processor (RTP). X-ray diffraction and Raman scattering measurements have shown that polycrystalline KLN films with tetragonal tungsten-bronze-type structure could be obtained on both SiO2 buffered Si and fused quartz substrates. Surface morphology studies indicated that RTP annealing could avoid film cracking and enable nanostructured low- surface roughness KLN films to be formed. Optical waveguiding experiments showed that the films have refractive indices close to those of their single crystal and could support several modes. The films deposited on fused quartz were highly transparent in the visible-near IR spectral range and the absorption edges of the films, as determined from the absorption data, were found to shift towards the violet spectral side.

Optical properties of potassium lithium niobate films

Abstract Potassium lithium niobate (KLN) thin films have been deposited on fused silica and MgO from metallorganic compounds through a sol-gel process. X-ray diffraction structure analysis has shown that KLN films crystallize into tetragonal tungsten-bronze-type phase after appropriate annealing. Crystallization of KLN films has a strong dependence on the structure of the substrates. Polycrystalline KLN films were obtained on fused quartz, whereas oriented KLN films have been achieved on MgO single crystal substrates. Optical studies have indicated that the films were highly transparent in the visible-near infrared wavelength range and the absorption edges of the films are also substrate-dependent. The films could support optical modes.