The effect of Zn 2＋ ions codoped on the upconversion emission of Er 3＋ ions in Er：LiNbO 3 crystal under different excitation wavelength was reported.The upconversion emission spectra of Zn/Er：LiNbO 3 following 800 nm excitation reveal an enhanced green emission and a suppressed red emission simultaneously.The cross relaxation processes（2 H11/2 ＋ 4 I13/2 → 4 I11/2 ＋ 4 F9/2 and 4 F7/2 ＋ 4 I11/2 → 4 F9/2 ＋ 4 F9/2） are responsible for populating the red 4 F 9/2 emitting state.The dissociation effect of Zn2＋ ions on the Er 3＋ cluster sites makes these cross relaxation processes inefficient.Under 980 nm excitation,the Zn 2＋ codoped leads to the decreased intensities of green and red upconversion emissions.These reductions are attributed to the inefficient cross relaxation processes（4 I11/2 ＋ 4 I11/2 → 4 F7/2 ＋ 4 I15/2 and 4 F7/2 ＋ 4 I11/2 → 4 F9/2 ＋ 4 F9/2） caused by the same dissociation effect of Zn 2＋ ions.
＜正＞In recent years,piezoresponse force microscopy（PFM） has become a powerful tool to investigate the electrome...
Kai PAN~1 Yun-Ya LIU~1 Jiang-Yu LI~(2,*) 1 Faculty of Materials,Optoelectronics and Physics,Key Laboratory of Low Dimensional Materials and Application Technology of Ministry of Education,Xiangtan University,Hunan 411105 2Department of Mechanical Engineering,University of Washington,Seattle,Washington 98195-2600
Ce-doped lithium niobate （LiNbO3） single crystals were grown from the melts with various Li/Nb molar ratios （0.750, 0.850, 0.946, 1.100, 1.250 and 1.380） by Czochralski method, while doping concentration of Ce was 0.1 mol%. Infrared spectra （IR） and Ultraviolet-visible absorption spectra （UV） of the crystals were measured to investigate the location of Ce ions and defect structure in crystals. The writing time, erasing time, photorefractive sensitivity and dynamic range were measured by two-wave coupling equipment. The results showed that Ce takes the place of Li lattice site, and the LiNbO3 crystal grown from the melt with Li/Nb ratio of 1.250 is stoichiometric crystal, which has the best properties due to the synergistic effect of Ce ion and Li/Nb ratio. Also the influence of various Li/Nb ratios on the defect structure and optical properties of the crystal was reported.
The enhanced intensity and lengthened lifetime of 1.54 μm emission were observed for Er：LiNbO3 crystal codoped with Zn2＋ ions.The ZnO codoping led to the reduction of the green upconversion emission in Er：LiNbO3 crystals.The decay trace of the 4S3/2→4I15/2 was ob-viously nonexponential for Er：LiNbO3 codoped with 0 and 3 mol.% ZnO,but became exponential for one codoped with 6 mol.% ZnO.The OH-absorption spectra showed after codoping with Zn2＋ ions,the OH-absorption peaking position shifted from ~3495 to 3484 cm-1,and the absorption cross section decreased.These spectroscopic characteristics suggested that the improvement of 1.54 μm emission was attributed to the reduction of Er3＋ cluster sites.
The vertical and lateral interactions in a multisheet array of InAs/GaAs quantum dots are analyzed by finite element method （FEM）. It is shown that due to the effects of vertical interaction, nucleation prefers to happen above buried quantum dots （QDs）. Meanwhile, the effects of lateral interaction adjust the spacing of lateral neighboring QDs. The vertical coupling becomes strong with deceasing GaAs spacer height and increasing number of buried layers, while the lateral coupling becomes strong with increasing InAs wetting layer thickness. The phenomenon that, after successive layers, the spacing and size of QDs islands become progressively more uniform is explained according to the minimum potential energy theory.
Sol-gel based soft lithography technique has been developed to pattern a variety of ferroelectric Pb（Zr0.52Ti0.48）O3（PZT） microstructures,with feature size approaching 180 nm and good pattern transfer between the master mold and patterned films.X-ray diffraction and high-resolution transmission electron microscopy confirm the perovskite structure of the patterned PZT.Piezoresponse force microscopy（PFM） and switching spectroscopy piezoresponse force microscopy（SSPFM） confirm their piezoelectricity and ferroelectricity.Piezoresponse as high as 2.75 nm has been observed,comparable to typical PZT films.The patterned PZT microstructures are promising for a wide range of device applications.
The optical properties of Er3＋-doped and Yb3＋/Er3＋ co-doped 12CaO·7Al2O3 （C12A7） poly-crystals, synthesized by high temperature solid state method, were investigated in detail. For Er3＋-doped and Yb3＋/Er3＋ co-doped C12A7 poly-crystals, two main emission bands centered around 530/550 nm （green） and 660 nm （red） were observed under 980 nm diode laser excitation via an up-conversion process. The intensity of green up-conversion emission had a strong increase in Er3＋ （1.0 mol.%, 1.5 mol.%, 3.0 mol.%）, and the intensity ratio of red to green up-conversion emission had an increase in Yb3＋ （1.0 mol.%, 2.0 mol.%, 10. 0 mol.%）/Er3＋ （fixed at 1.0 mol.%）. This detailed study of the up-conversion processes allowed us to identify the dominant up-conversion mechanisms in Er3＋-doped and Yb3＋/Er3＋ co-doped C12A7 poly-crystals.
＜正＞The prospect of manipulating magnetic orderings by electric field in multiferroic materials has generated g...
Yun-Ya LIU Kai PAN Jiang-Yu LI 1 Faculty of Materials,Optoelectronics and Physics.Key Laboratory of Low Dimensional Materials and Application Technology of Ministry of Education,Xiangtan University.Hunan 411105 2 Department of Mechanical Engineering,University of Washington.Seattle,Washington 98195-2600
The IR-to-visible upconversion fluorescent crystals, Yb：Ho：LiN-bO3, with a constant Ho^3＋ concentration （0.1 mol%） and different doping concentrations of Yb^3＋ （0.5, 1.5, 2.0, 2.5, 3.0 tool%） are synthesized by Czochralski method in air atmosphere. X-ray diffraction shows that the obtained crystal is a single phase of LiNbO3 and the rare-earth ions occupied the Li^＋ or Nb^5＋ sites instead of the interstitial sites. Under 980 nm excitation, green and red emission bands due to the Ho^3＋ （^5S2, ^5F4）/^5I8 and Ho^3＋ ^5F5/^5I8 energy transitions are observed in these samples, respectively. Power dependence studies on these samples with different Yb^3＋ dopant concentrations indicate that the red and green emissions are based on a two-photon process. The intensities of the red and green upconversion fluorescence increase with Yb3＋ ions of 0-2.0 mol% because of an increased Yb^3＋ sensitization, but decrease at higher concentrations owing to the back-energy transfer between the Yb^3＋ and Ho^3＋ ions.
