Bin Zhao

A new technique to grow incongruent melting Ga:YIG crystals: the edge-defined film-fed growth method

Crystalline yttrium iron garnet (YIG) is an important magneto-optical material. However, this crystal is an incongruent melting compound. As is well known, compared to the crystal growth of a congruent melting compound by using the Czochralski method, the crystal growth of an incongruent melting compound is more difficult. In this work, a system for growing Ga:YIG single crystals by the edge-defined film-fed growth (EFG) method was designed and constructed, and the mechanism of crystal growth was also preliminarily studied. The Ga3+ dopant concentration, the Curie temperature and the transmission spectra of as-grown crystals were investigated to evaluate their potential application in magneto-optical devices. The success of growing Ga:YIG crystals by the EFG method provides a new way to grow other incongruent melting compounds.

GROWTH, OPTICAL AND MAGNETIC PROPERTIES OF Co-DOPED TiO2 CRYSTAL

Co-doped TiO2 crystals (Co:TiO2) were grown by Czochralski growth (CZ) method and the edge-defined film-fed growth (EFG) method, respectively. Therein, EFG was an effective method to grow a higher quality Co:TiO2 crystal without the reverse flow of the melt. This as-grown crystal reaches a larger dimension of 10 mm × 15 mm × 18mm. XRD analysis confirms that as-grown crystal is isostructural with TiO2 rutile phase. Moreover, this crystal has ferromagnetism at room temperature and the magnetic moment of Co ion is 1.25 × 10-2 μB/Co. After annealed at 1273 K, Co:TiO2 crystal enhances obviously its optical transmittance, while this crystal shows diamagnetism due to the disappearance of the ferromagnetic signal.

Growth, Faraday and inverse Faraday characteristics of Tb 2 Ti 2 O 7 crystal

Tb2Ti2O7 (TTO) single crystal with dimensions of 20 × 20 × 16 mm3 was grown by the Czochralski method. Rietveld structure refinement of X-ray diffraction (XRD) data confirms that the compound crystallizes in the cubic system with pyrochlore structure. Transmission spectra, Magnetic circular dichroism (MCD) spectra, Faraday and inverse Faraday characteristics of TTO crystal have been measured and analyzed in detail. The results demonstrate that TTO crystal has high transmittance at 700-1400 nm waveband and a larger Verdat constant than that of TGG reported. Magnetic circular dichroism (MCD) spectra showed that the 4f→4f transitions of Tb3+ have significant contributions to the magneto-optical activity (MOA). In the time-resolved pump-probe spectroscopy, the rotation signals of the probe beam based on the inverse Faraday effect in magneto-optical crystal were observed at zero time delay, the full width at half maximum of the rotation and ellipticity signals can be as fast as ~500 fs, which indicates that TTO crystal can be a promising material for ultrafast all-optical magnetic switching.

Mild preparation and high fluorescence emission efficiency of europium-doped gallium nitride nanocrystals and first-principles density functional theoretical analysis of optical properties

Europium-doped gallium nitride (Eu:GaN) nanocrystals with hexagonal wurtzite structures were prepared from the decomposition of the EuxGa1−x(H2NCONH2)6Cl3 precursor at a mild temperature of 350 °C. The absorption spectrum, the excitation spectra and the fluorescence emission spectra of Eu:GaN nanocrystals are measured and discussed. Eu:GaN has a strong fluorescence emission band in the visible region. Furthermore, the first-principles density functional theory has been adopted to explore the fluorescence mechanism. The results show that energy transfer should occur between the GaN host and Eu3+ ions under excitation at 370 nm, and thus the fluorescence emission efficiency of the Eu3+ ions can be improved. In order to further reduce the loss of fluorescence emission and increase the fluorescence quantum yield, Eu:GaN nanocrystals coated by biocompatible silica and dispersed in ethanol are also discussed.