Surface excitonic emission and quenching effects in ZnO nanowire/nanowall systems: limiting effects on device potential.

We report ZnO nanowire/nanowall growth using a two-step vapour phase transport method on a-plane sapphire. X-ray diffraction and scanning electron microscopy data establish that the nanostructures are vertically well-aligned with c-axis normal to the substrate, and have a very low rocking curve width. Photoluminescence data at low temperatures demonstrate the exceptionally high optical quality of these structures, with intense emission and narrow bound exciton linewidths. We observe a high energy excitonic emission at low temperatures close to the band-edge which we assign to the surface exciton in ZnO at ~ 3.366 eV, the first time this feature has been reported in ZnO nanorod systems. This assignment is consistent with the large surface to volume ratio of the nanowire systems and indicates that this large ratio has a significant effect on the luminescence even at low temperatures. The band-edge intensity decays rapidly with increasing temperature compared to bulk single crystal material, indicating a strong temperature-activated non-radiative mechanism peculiar to the nanostructures. No evidence is seen of the free exciton emission due to exciton delocalisation in the nanostructures with increased temperature, unlike the behaviour in bulk material. The use of such nanostructures in room temperature optoelectronic devices appears to be dependent on the control or elimination of such surface effects

SrBi2Nb2O9 thin films epitaxially grown on Pt epitaxial bottom layers: structural characteristics and nanoscale characterization of the ferroelectric behaviour by AFM

SrBi2Nb2O9 (SBN) films were grown by pulsed laser deposition on (400) and (110) Pt epitaxial bottom layers. In both cases x-ray diffraction evidenced the epitaxial growth of SBN in spite of the coexistence of mainly two orientations. SBN films on (100) Pt present usually a dominant (001) orientation with the (115) one. AFM piezoresponse images agree with the crystallographic data, i.e. only the (115) oriented grains show a piezoelectric contrast. The SBN films grown on (I 10) Pt lead to a more homogenous piezoresponse imaging, in agreement with the preferential (116) orientation and the microstructure. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Exploring the optical properties of the 1.53 μm emission in Er3+-doped glass, anti-glass and ceramic in TeO2 - Ta2O5 - Bi2O3 system

International audienceA series of 80TeO2 - 10Ta2O5 – 10Bi2O3 glasses, anti-glasses and ceramics doped with different concentrations of Er₂O₃, ranging from 0.25 % to 2 % mol, were synthesized to explore their structural transformation and optical properties. The maximum solubility of Er₂O₃ was identified at 1.25 % mol, beyond which the glass transitioned from an amorphous to a crystalline structure. The anti-glasses and ceramics obtained from the heat treatment of the parent glasses were also studied to gain insights into their optical properties. This study reveals a direct relationship between Er3+ ions concentration and full width at half maximum (FWHM) of photoluminescence spectra. The increase in Er3+ ions concentration correlates with a rise in FWHM, indicative of spectral broadening. Anti-glass exhibits a higher emission intensity, followed by ceramic and then glass, reflecting their distinct structural properties. Anti-glass doped with 1 % mol Er2O3 shows an FWHM over 130 nm under 578 mW pumping. The lifetime of the excited state 4I13/2 increases with the Er2O3 content in the anti-glass and the ceramic, with a notable decrease at 1 % mol Er2O3 ions for both materials, while in glass, the decrease is observed at 0.5 %. Emission cross-sections decrease with increasing Er3+ ions concentration and power, influenced by factors like thermal effects and saturation. The Judd-Ofelt theory highlights structural differences, with glasses having a more disordered structure and with an increase in the Ω₆ parameter across all materials, implying enhanced electric dipole line strength and spontaneous emission probability with higher Er₂O₃ content. Overall, this comprehensive study provides valuable insights into the optical behavior of Er3+ ions in these materials, essential for applications in laser design and optical amplifiers

Broadband luminescence of Ni2+-doped Zn(GaxAl1−x)2O4-based glass–ceramics

International audienceNi2+‐doped glass–ceramics containing Zn(GaxAlx−1)2O4 crystals were successfully synthetized using both parent glass crystallization (Technique 1) and a direct doping method also called “frozen sorbet” (Technique 2) to get a ZnGa2O4 crystal/glass composite. The frozen sorbet technique allows the survival of ∼10 nm crystalline particles. Both materials are further crystallized near their respective temperature of crystallization to get glass–ceramics with the stabilization of Zn(GaxAlx−1)2O4 crystals. Although these two materials exhibit the same glass transition temperature, a shift in the crystallization temperature is observed. The glass–ceramics are transparent in the near infrared range, and the Ni2+ doping provides a broadband emission centered around 1300 nm with a full width at half‐maximum (FWHM) equal to 228 nm. The structure, microstructure, and thermal and optical properties of these materials are discussed in the present study

Comparative Analysis of the Electronic Structure and Nonlinear Optical Susceptibility of α-TeO 2 and β-TeO 3 Crystals

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Fabrication and optical properties of transparent fine-grained Zn1.1Ga1.8Ge0.1O4 and Ni2+ (or Cr3+)-doped Zn1.1Ga1.8Ge0.1O4 spinel ceramics

International audienceFor the first time, a Zn1.1Ga1.8Ge0.1O4 transparent spinel ceramic has been fully densified by spark plasma sintering. XRD measurements show that this ceramic is composed of a pure cubic spinel phase. SEM analysis revealed a homogeneous and dense microstructure with the average grain size being 200 ± 100 nm. The transmittance of these fine-grained ceramics reached 70 % in the visible range and is very close to 80 % at 2 µm, thus close to the Tmax value deduced from the measurement of the refractive index. The ceramics exhibit excellent mechanical properties with a Young modulus of 222 GPa, a Vickers hardness of 14.25 GPa and a thermal conductivity of 7.3 W.m−1. K−1. By doping with Cr3+ ions, transparent Zn1.1Ga1.8Ge0.1O4 ceramics present both a red luminescence and a long-lasting afterglow during several minutes. Moreover, a near infrared broadband emission at 1.3 µm is also achieved with Ni2+ ions

Highly transparent bismuth borotellurite glass-ceramics: Comprehension of crystallization mechanisms

International audienceUnderstanding the mechanism at play during the partial crystallization of a parent glass remains crucial for controlling the optical properties of the final glass-ceramics. In this work, we study the crystallization of bismuth borotellurite glasses, where a specific investigation on the 60TeO2–20B2O3–20Bi2O3 composition is reported. Under adapted heat treatment conditions, highly transparent glass-ceramics can be obtained: the crystallization of the unique anti-glass Bi2Te4O11 phase is evidenced by X-ray diffraction and Raman spectroscopy data confirm its disordered nature. While the quenched glass appears homogeneous, the observation of the early stages glass-ceramic samples by transmission electron microscopy reveals the formation of isolated polycrystalline Bi2Te4O11 entities scattered in a predominant glassy matrix. However, longer heat-treatment of samples induce some chemical demixtion of the residual glass matrix, where two separate amorphous regions of a different composition coexist. The resulting material is finally constituted of the aforementioned Bi2Te4O11 polycrystalline clusters dispersed within a majority of regions with a Te/Bi ratio larger than the nominal 1.5 ratio, separated by tiny “venules” strongly impoverished in tellurium and also likely containing boron element. Photoluminescence properties of Eu3+-doped samples indicate that tiny spectral and temporal modifications happen with the crystallization, reflecting the persistent disordered surrounding of the rare-earth ions. © 202

Third order nonlinear optical properties of a paratellurite single crystal

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