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The extinction spectra of a three-layered metal nanoshell, which consists of a particle with a dielectric core, a middle Ag (Au) layer, and an outer Au (Ag) shell, have been investigated by means of the Mie theory. With a decrease in the outer shell thickness or the middle layer thickness, the wavelengths of the localized surface plasmon resonance (LSPR) for SiO2–Ag–Au (SiO2–Au–Ag) nanoshells show distinct redshifts and the full widths at half maximum (FWHMs) for the dipole peaks in the extinction spectra decrease first and then increase. We have further investigated the influence of the embedding medium on the LSPRs for SiO2–Ag–Au and SiO2–Au–Ag nanoshells and found that the resonance wavelengths of the particles show redshift and the FWHM of the dipole peak increases with increasing the dielectric constant of the embedding medium. The calculated results indicate that the LSPR of the three-layered gold-silver nanoshells can be controlled to the near-infrared region by changing the geometry, which has practical biomedical application. [ABSTRACT FROM AUTHOR]

The growth, XRD patterns, spectral properties, and fluorescence decays of Yb:Ca 0.28 Ba 0.72 Nb 2 O 6 (Yb:CBN) with doping concentration of 1 at.% and 5 at.% were studied. The peak absorption cross-section and the emission cross-section were calculated. Larger Stark splitting of Yb:CBN offers the prospect of the quasi-four level laser operation. The fluorescence lifetimes are 0.64 and 0.73 ms for 1 at.% and 5 at.%, respectively. The FWHM of absorption and fluorescence spectra of 5 at.% Yb:CBN are 62 and 68 nm, which are broader than other ultrashort laser media. The results prove that Yb:CBN crystal is a good candidate as an ultrashort laser medium. [ABSTRACT FROM AUTHOR]

CuO feather-like and flower-like crystals have been synthesized by a fast microwave-assisted solution approach using Cu(NO3)2 and NaOH. The morphology transformation of CuO could be achieved by ionic liquid 1-n-butyl-3-methyl imidazolium tetrafluoroborate ([BMIM]BF4). With [BMIM]BF4, flower-like CuO were obtained, whereas without [BMIM]BF4, feather-like CuO were obtained. The possible formation mechanism of flower-like CuO was discussed on the basis of experimental results. The products were characterized by XRD, FESEM/EDS, and TEM/SAED. In addition, the adsorption of [BMIM]BF4 on flower-like CuO was confirmed by FTIR and TG/DSC, and the band gap energies of the flower-like CuO was estimated by UV-vis spectra. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) CuO nanoplatelets were synthesized in the presence of ionic liquids under the mild hydrothermal conditions at 140°C by self-assembly. The thickness of CuO nanoplatelets was about 35 nm prepared in 1-butyl-3-methylimidazolium chloride. XRD, FESEM, and TEM were used to characterize the structure features of the products. FTIR spectra and TG curves confirmed the adsorption of ionic liquids on the surface of CuO nanoplatelets. In addition, UV-visible absorption spectra were employed to estimate the band gap energies of the CuO nanoplatelets as nanosized semiconductors. It was demonstrated that the ionic liquids could act as a cosolvent, soft template agent and modifiers. [ABSTRACT FROM AUTHOR]

Abstract: Absorption and emission spectral properties of GdVO4 single crystal doped with Ho3+ ions were investigated at room temperature. Polarized absorption cross section is calculated in the range of 400–2200nm. Results were analyzed and parameters were calculated based on Judd-Ofelt theory, the emission spectrum shows that the emission intensity around the wavelength of 546nm associated with transition 5S2 → 5I8 is much stronger than other bands in the observed range and potentially enable the green light output around this emission band in this crystal. [Copyright &y& Elsevier]

Abstract: Yb:Y3Al5O12 (Yb:YAG) single crystals with Yb doping concentration 0.5at.%, 5at.%, 15at.%, 25at.%, 50at.%, 100at.% and Yb:YAlO3 (Yb:YAP) single crystals with Yb doping concentration 0.5at.%, 5at.%, 15at.%, 30at.% were grown by the Czochralski process. The fluorescence spectra of these crystals and the effects of self-absorption on the shape of the fluorescence spectra were studied. Through comparing the fluorescence spectra of Yb:YAG and Yb:YAP, all results indicate that the effects of self-absorption on the fluorescence spectra of Yb:YAP are remarkably stronger than that of Yb:YAG at the same Yb concentration. [Copyright &y& Elsevier]

Abstract: Absorption spectrum from 400 to 2000nm and upconversion fluorescence spectra under 940nm pumping of YAG single crystal codoped with 5at.% Yb3+ and 4at.% Tm3+ were studied at room temperature. The blue upconversion emission centered at 483nm corresponds to the transition 1G4 → 3H6, the emission band around 646nm corresponds to the transition 1G4 → 3F4 of Tm3+. Energy transfer from Yb3+ to Tm3+ is mainly nonradiative and the transfer efficiency was experimentally assessed. The line strengths, transition probabilities and radiative lifetimes of 1G4 level were calculated by using Judd–Ofelt theory. Gain coefficient calculated from spectra shows that the upconversion corresponding with transitions 1G4 → 3H6 in YAG doped with Yb3+ and Tm3+ is potentially useful for blue light output. [Copyright &y& Elsevier]

Abstract: Yb3Al5O12 single crystal has been grown by Czochralski (CZ) method. The absorption spectrum was investigated at low temperature and the electronic energy levels for 2F5/2 multiplet of Yb3+ in YbAG was proposed. The up-conversion emission of the crystal under 940nm diode pumping and the X-ray excited luminescence (XEL) features of the crystal were also studied. [Copyright &y& Elsevier]

Abstract: In this paper, we present results on upconversion luminescence performed on Yb3+-doped yttrium aluminum garnets under 940nm excitation. The upconversion luminescence was ascribed to Yb3+ cooperative luminescence and the presence of rare earth impurity ions. The cooperative luminescence spectra as a function of Yb concentration were measured and the emission intensity variation with Yb concentration was discussed. Yb3+ energy migration quenched the cooperative luminescence of Yb:YAG crystals with doping level over 15at%. [Copyright &y& Elsevier]

The absorption spectra, emission under 940 nm excitation by laser diode, and fluorescence lifetimes of as-grown and annealed Cr,Yb:YAG crystal have been investigated at room temperature. The increase of absorption coefficients at 941 and 1030 nm and the quenching of Yb3+ emission intensity and fluorescence lifetime after annealing are due to the increase of the concentration of Cr4+ ions. The data of thermal expansion and specific heat of the crystal have been measured. The thermal expansion coefficient is α=8.71×10−6 /K. The specific heat is 89.9 cal/mol K at 320.5 K. [Copyright &y& Elsevier]

The Czochralski crystal growth of 50 at.% Yb:YAG single crystal was reported. The absorption spectrum, emission spectrum and fluorescence lifetime of Yb:YAG crystal were measured at room temperature. The spectroscopic parameters of nominal 50 at.% Yb:YAG crystal were compared with that of Yb:YAG crystal with low doping level. The results indicate that Yb:YAG crystals with high doping level are potential candidates used for compact, efficient thin chip lasers. [Copyright &y& Elsevier]

Five atomic percent Yb:YAG laser crystals have been grown by Czochralski (CZ) and temperature gradient technique (TGT) method. The absorption spectra of as-grown and annealed Yb:YAG crystals have been investigated. There is no Yb2+ and color center absorption in TGT-grown Yb:YAG crystals; the absorption peak of CZ-grown Yb:YAG crystals after O2-annealing at 255 nm is attributed to Fe3+ ions. The longitudinal distribution of Yb3+ ions has also been studied; TGT-grown Yb:YAG crystal has a larger distributing inhomogeneity of Yb3+ although it is large sized. [Copyright &y& Elsevier]

The potential and limitations of Rayleigh wave spectroscopy to characterize the elastic depth profile of heterogeneous functional gradient materials are investigated by comparing simulations of the surface acoustic wave dispersion curves of different profile-spectrum pairs. This inverse problem is shown to be quite ill posed. The method is then applied to extract information on the depth structure of a glass-ceramic (alumina) functionally graded material from experimental data. The surface acoustic wave analysis suggests the presence of a uniform coating region consisting of a mixture of Al2O3 and glass, with a sharp transition between the coating and the substrate. This is confirmed by scanning electron microscope with energy dispersive x-ray analysis. [ABSTRACT FROM AUTHOR]

In this paper, we describe a thulium-doped (Lu,Y) 3 Al 5 O 12 mixed crystal that was designed and grown to achieve a large pulse energy in Q-switched laser operation. Its absorption cross-sections at 781.3 nm and 1629.2 nm were calculated to be 3.4 × 10 −21 cm 2 and 5 × 10 −21 cm 2 , respectively, and the emission cross-section at 2018.3 nm was calculated to be 1.92 × 10 −21 cm 2 . The highest single pulse energy of 1.4 mJ near 2.02 μm was realized in an actively Q-switched solid-state laser, and further power scaling was just limited by the damage of the crystal coating. Based on the calculated spectrum parameters, theoretical simulation of the single pulse energy that considering the cross-relaxation process was proposed, which was well consistent with the experimental results. [ABSTRACT FROM AUTHOR]

Abstract: The Cr(0.1%),Yb(10%):GGG crystals have been grown by the Czochralski method. The chemical composition is: Yb0.33Gd2.47Cr0.005Ga5.2O12. There are no observed Yb3+ ions substituting Ga3+ ions, just like that of Yb:GGG crystals. The defects in Cr,Yb:GGG crystal were also investigated. The absorption and emission spectra of Cr,Yb:GGG crystal at room temperature have been measured. The O2 and H2 annealing effect of Cr,Yb:GGG crystal have been compared. Cr3+ can greatly weak the visible luminescence of this crystal. The Cr–Yb-codoped crystals may be potential materials for compact, efficient, high stability LD pumped solid state lasers. [Copyright &y& Elsevier]

Abstract: In this paper, single crystal of ytterbium (Yb) doped Ca5(PO4)3F (FAP) has been grown along the c-axis by using the Czochralski method. The segregation coefficients of Yb3+ in the Yb:FAP crystal has been determined by ICP-AES method. The absorption spectrum, fluorescence spectrum and fluorescence lifetime of the Yb:FAP crystal has been also measured at room temperature. In the absorption spectra, there are two absorption bands at 904 and 982nm, respectively, which are suitable for InGaAs diode laser pumping. The absorption cross-section (σ abs) is 5.117×10−20 cm2 with an FWHM of 4nm at 982nm. The emission cross-section (σ em) is 3.678×10−20 cm2 at 1042nm. Favorable values of the absorption cross-section at about 982nm are promising candidates for laser diode (LD) pumping. [Copyright &y& Elsevier]

Abstract: Growth-induced defects in Yb:FAP crystals grown by the Czochralski method have been investigated by optical microscopy, chemical etching, scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). Anisotropic etching features have been observed on two FAP crystal planes: (0001) and . The shape of etch pits on the (0001) plane is hexagonal, while the etch pits on the plane have a variety of irregular shapes. It is also found that the density of etch pit varies along the boule. Based on the experimental observations, the formation mechanisms of growth defects are discussed, and methods for reducing the growth-induced defect concentration is proposed. [Copyright &y& Elsevier]

Abstract: The Yb (10%):GGG and Yb (30%): GGG crystals have been grown by the Czochralski method. The chemical compositions are: Yb1.07Gd1.74Ga5.19O12 and Yb0.33Gd2.47Ga5.2O12. The absorption and emission spectra of Yb:GGG crystal at room temperature have been measured. The spectroscopic parameters of Yb:GGG and Yb:YAG have been compared. Optical absorption spectra of Yb:GGG show 4f–4f transitions related to Gd3+ ion around 300nm, and also an onset of charge transfer (CT) transitions from oxygen ligands to Gd3+ or Yb3+ cations below 240nm.The CT absorption of Yb3+ is largely overlapped by that of Gd3+ ions. [Copyright &y& Elsevier]

Abstract: Yb: YAlO3 (YAP) (15at%) and Yb: Y3Al5O12 (YAG)(15at%) have been grown using the Czochralski method. Their absorption and fluorescence spectra were measured at room temperature and important spectroscopic parameters were calculated. Through the comparison of spectroscopic parameters of Yb:YAP and Yb: YAG, all results indicate that 15at% Yb:YAP crystal is a potential candidate used for compact, efficient thin chip lasers when the laser output wavelength is 1012 or 1038nm. [Copyright &y& Elsevier]

Abstract: The high optical quality Tm: YAG single crystals with dopant concentrations of 2, 4, 8 at % Tm3+ ions have been grown by the Czochralski (CZ) method .The segregation coefficients of Tm3+ ions in CZ-grown 2, 4, 8 at % doped Tm: YAG crystals determined by ICP-AES method are equal to 0.93, 1.04, 1.10, respectively. The absorption spectra in the range of 190–900nm and the IR absorption spectra in the range of 1000–4500cm-1 of the Tm: YAG crystals were also measured at room temperature. The results indicate that Tm: YAG is favorable for laser diode-pumped system, and air annealing can improve the quality of the Tm: YAG crystal. [Copyright &y& Elsevier]

Recent reports have shown that self-assembled monolayers (SAMs) can induce doping effects in graphene transistors. However, a lack of understanding persists surrounding the quantitative relationship between SAM molecular design and its effects on graphene. In order to facilitate the fabrication of next-generation graphene-based devices it is important to reliably and predictably control the properties of graphene without negatively impacting its intrinsic high performance. In this study, SAMs with varying dipole magnitudes/directions are utilized and these values are directly correlated to changes in performance seen in graphene transistors. It is found that, by knowing the z-component of the SAM dipole, one can reliably predict the shift in graphene charge neutrality point after taking into account the influence of the metal electrodes (which also play a role in doping graphene). This relationship is verified through density functional theory and comprehensive device studies utilizing atomic force microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and electrical characterization of graphene transistors. It is shown that properties of graphene transistors can be predictably controlled with SAMs when considering the total doping environment. Additionally, it is found that methylthio-terminated SAMs strongly interact with graphene allowing for a cleaner graphene transfer and enhanced charge mobility. [ABSTRACT FROM AUTHOR]

Abstract: Spectroscopic properties of lutetium aluminum garnet Lu3Al5O12 (LuAG) single crystal doped with 1at.% of Pr3+ were investigated. The crystal was grown by the Czochralski method. Optical absorption, emission, excitation spectra and luminescence decay curves were recorded for this system in 5–500K temperature range. Excitation spectra in VUV–UV range (150–330nm) were also measured exploiting synchrotron radiation. It has been found that among bands of luminescence related to the 3PJ, 1D2 → 3HJ, 3FJ transition of Pr3+ in the visible region the 3P0 → 3H4 one, occurring ca. 488nm, is the most prominent. Luminescence lifetimes for the 3P0,1 and 1D2 levels were estimated to be 13 and 200μs respectively (at room temperature). VUV-excited emission spectrum stretches over the whole visible region. It has been concluded that the material under study is a promising phosphor that can be efficiently pumped by broad absorption bands centered at 240 and 280nm. [Copyright &y& Elsevier]

Abstract: Ytterbium-doped calcium pyroniobate single crystal has been grown for the first time. Spectral properties of Yb: Ca2Nb2O7 were investigated by emission and absorption spectra. Its cooperative luminescence and fluorescence lifetime were also studied. Yb ions in Ca2Nb2O7 showed very broad absorption and emission bandwidth and relatively large absorption and emission cross-sections. Along with other optical properties, this Yb-doped crystal would be a potential self-frequency doubling femtosecond laser gain material. [Copyright &y& Elsevier]

Abstract: Gd2SiO5 (GSO) single crystal codoped with Yb3+ and Er3+ (Abbr. as Er:Yb:GSO) was successfully grown by the Czochralski (CZ) method for the first time and the spectral characteristics were investigated. The absorption and fluorescence spectra were measured. The emission lifetime of the 4I13/2–Er-level was measured to be 5.84ms and the emission cross-section at 1529nm was calculated to be 1.03×10−20 cm2. The results indicate that Er:Yb:GSO is a potential laser material at ∼1.55μm wavelength region. [Copyright &y& Elsevier]