Yingyin K. Zou

Synthesis and Characterization of YAG : Ce3 + LED Nanophosphors

Nanophosphors of Y 3 Al 5 O 12 /Ce 3+ (YAG/Ce) were synthesized with a novel salted sol-gel (SSG) method in which a water solution of inorganic salt, yttrium nitrate [Y(NO 3 ) 3 , YNO], was used with a traditional metal alkoxide precursor, aluminum sec-butoxide [Al(OC 4 H 9 ) 3 , ASB], in sol-gel synthesis. With the SSG method, a YAG single phase could be obtained by sintering the dry gel of Al 2 O 3 and Y 2 O 3 mixture for 2 h at 800°C. The YAG particle size was in a range from 30 to 100 nm. Luminescence properties of the YAG samples with different Ce 3+ doping concentrations were studied. The peak intensity of luminescence was found at 4% Ce 3+ doping concentration. Red shift of the emission peaks was observed when the doping concentration was increased.

Optical amplification in Nd3+ doped electro-optic lanthanum lead zirconate titanate ceramics

As high as 13.0dB single-pass gain was obtained at 1064.4nm in a thin electro-optic ceramic plate of neodymium doped lanthanum-modified lead zirconate titanate (Nd:PLZT). Pumping with a diode laser, gains were achieved in 1.0 and 0.5mol% Nd ion doped samples over a broad seed laser power ranging from tens of nanowatts to tens of milliwatts at room temperature. The broad absorption spectra of Nd:PLZT made it insensitive to the pump wavelength. The Nd:PLZT had a total scattering loss coefficient of less than 0.06cm−1 and exhibited a considerable quadratic electro-optic coefficient greater than 0.30×10−16m2∕V2.

Lasing action and optical amplification in Nd 3+ doped electrooptic lanthanum lead zirconate titanate ceramics

Both single-pass gain and lasing action at 1064.4 nm were observed in ceramic gain media of neodymium doped lanthanum-modified lead zirconate titanate, which exhibits good electrooptic (EO) effect from visible through mid-wave IR band (400 nm to 5.5 µm). These works have removed roadblocks off the way leading to development of long envisioned multifunctional optical devices. The impact of the Nd3+ doping concentration on the EO effect in the Nd3+:PLZT ceramics was studied. The finding of the slowly trailing-off was satisfactorily explained with the rich vacancy-based carrier traps, which are responsible for the long persistent optoenergy storage.

Optoenergy storage, stimulated processes in optical amplification with electro-optic ceramic gain media of Nd3+ doped lanthanum lead zirconate titanate

Optical amplification was observed in electro-optic (EO) ceramic plates of neodymium doped lanthanum-modified lead zirconate titanate (Nd3+:PLZT), when the pumping and seeding beams are not overlapped temporarily. This striking feature in the gain measurement and the accompanying slowly trailing-off both seen in the optical amplification as well as in the lasing action are satisfactorily explained by electron releasing from the rich vacancy-based carrier traps in the intrinsically disordered ceramics, i.e., the consecutively optical, thermal stimuli are found responsible for the long persistent optoenergy storage, and consequently the slow response of the gain dynamics. These findings in optical amplification, the slowly trailing-off, and the underlying mechanism have opened a new way of developing novel controllable optical devices. The model thus established could serve as a guide in design and refinement of a new generation of products out of this excellent, well commercialized EO PLZT ceramics family ...

Impact of grating spacing and electric field on real time updatable holographic recording in nanoscale ZnSe film assisted liquid crystal cells

Real time updatable holographic recording was demonstrated in C60 doped 4,4′-n-pentylcyanobiphenyl liquid crystal cells made of indium tin oxide glass plates covered with nanoscale ZnSe thin films, without aligning layers required. Possible governing mechanism behind the associated findings was proposed and supported experiments were presented, based on the excellent charge carrier generation/migration in the ZnSe and liquid crystal layers and near the ZnSe/liquid crystal interfaces.

Electroinduced structural change- and random walks-based impact on the light emission in Er3+/Yb3+ doped (Pb,La)(Zr,Ti)O3 ceramics

Remarkable enhancement/reduction of light emission and competition among different wavebands with rare earth doped lanthanum lead zirconate titanate ceramics were observed in a corona atmosphere caused by an externally applied electric field. Quantum-mechanical analyses, based on variation of structural symmetry of the unit cell and hence the crystal field due to electrostriction, were given to elucidate the effect. Apart from the symmetry of crystal field, the obvious contribution from the optoenergy storage and weak localization of light involved were discussed. These results are promising in designing and implementation of lasers and sensors.

Optoenergy storage and random walks assisted broadband amplification in Er3+-doped (Pb,La)(Zr,Ti)O3 disordered ceramics.

A broadband optical amplification was observed and investigated in Er3+-doped electrostrictive ceramics of lanthanum-modified lead zirconate titanate under a corona atmosphere. The ceramic structure change caused by UV light, electric field, and random walks originated from the diffusive process in intrinsically disordered materials may all contribute to the optical amplification and the associated energy storage. Discussion based on optical energy storage and diffusive equations was given to explain the findings. Those experiments performed made it possible to study random walks and optical amplification in transparent ceramics materials.

Wavelength translation based on photoinduced broadband absorption in Nd3+ -doped lanthanum lead zirconate titanate ceramics.

A correlation between a photoinduced broadband absorption (BBA) and a strong long persistent optoenergy storage (LPOES), both evident in ceramic plates of neodymium-doped lanthanum-modified lead zirconate titanate (Nd:PLZT), has been proposed and verified experimentally. As a direct evidence of the suggested correlation, a 3.0 dB gain was obtained with a preilluminated Nd:PLZT plate by simply heating up the plate to 60 degrees C. Thermal history related gain profiles taken in an Nd:PLZT plate unveiled that the intrinsically rich carrier traps in the ceramics are highly responsible for the remarkable BBA and underlying LPOES, and hence thermal to near-IR wavelength translation.

Backward optical gain originating from weak localization strengthened three-photon process in Er/Yb co-doped (Pb,La)(Zr,Ti)O 3 ceramics.

The enhancement of green upconverted emission from the Er3+/Yb3+ co-doped (Pb,La)(Zr,Ti)O3 ceramic powder under a pumping light with a wavelength of 1480 nm was observed to be greater than 30 times that from the bulk of the same sample. Weak localization of light supported by the spatial profile of scattered light facilitated the three-photon process contributing to stronger green upconverted emission. Significant backward light amplification was also observed and studied in detail. Additionally, the distribution of the localization zones in the sample was investigated using a probing laser beam with a wavelength of 532 nm. The findings in this work could be used in improving the solar cell efficiency, modulating color, and designing smart devices.

ELECTRO-OPTIC EFFECTS OF La-MODIFIED PMN-PT THIN FILMS FOR WAVEGUIDE APPLICATIONS

ABSTRACT Lanthanum-modified lead magnesium niobate titanate (PLMNT) thin films were fabricated on glass, silicon and sapphire substrates successfully via a chemical solution deposition process. The PLMNT thin films exhibited large electro-optic (EO) coefficients with La concentrations between 2.0–2.5 mol%. The largest EO coefficient was measured in a PLMNT thin film about 1 μ m thick deposited on r-cut sapphire substrate. The effective EO coefficient r 31 measured at 532 nm was as large as 1079 pm/V.