Post-exchange Annealing Research Articles

Ag-Sensitized NIR-Emitting Yb3+-Doped Glass-Ceramics

The optical photoluminescent (PL) emission of Yb3+ ions in the near infrared (NIR) spectral region at about 950–1100 nm has many potential applications, from photovoltaics to lasers and visual devices. However, due to their simple energy-level structure, Yb3+ ions cannot directly absorb UV or visible light, putting serious limits on their use as light emitters. In this paper we describe a broadband and efficient strategy for sensitizing Yb3+ ions by Ag codoping, resulting in a strong 980 nm PL emission under UV and violet-blue light excitation. Yb-doped silica–zirconia–soda glass–ceramic films were synthesized by sol-gel and dip-coating, followed by annealing at 1000 °C. Ag was then introduced by ion-exchange in a molten salt bath for 1 h at 350 °C. Different post-exchange annealing temperatures for 1 h in air at 380 °C and 430 °C were compared to investigate the possibility of migration/aggregation of the metal ions. Studies of composition showed about 1–2 wt% Ag in the exchanged samples, not modified by annealing. Structural analysis reported the stabilization of cubic zirconia by Yb-doping. Optical measurements showed that, in particular for the highest annealing temperature of 430 °C, the potential improvement of the material’s quality, which would increase the PL emission, is less relevant than Ag-aggregation, which decreases the sensitizers number, resulting in a net reduction of the PL intensity. However, all the Ag-exchanged samples showed a broadband Yb3+ sensitization by energy transfer from Ag aggregates, clearly attested by a broad photoluminescence excitation spectra after Ag-exchange, paving the way for applications in various fields, such as solar cells and NIR-emitting devices.

Моделирование кривых дифракционного отражения рентгеновских лучей от протонообменных слоев монокристалла ниобата лития

In this work, within the framework of the dynamic theory of the X-ray scattering, a model is constructed that describes the diffraction reflection curves obtained from the proton-exchange layers of a lithium niobate monocrystal subjected to the post-exchange annealing. Planar proton-exchange waveguides based on the X-cut of the lithium niobate monocrystal are obtained experimentally. It was shown that the proton implantation leads to the formation of the new crystalline phases with a larger lattice parameter. The structure changes (by the method of the diffraction structural analysis) and the optical properties (by the method of the mode spectroscopy) of the obtained waveguides are investigated in the various temperature regimes. The microstrain of the crystal lattice caused by еру proton implantation was estimated by the analysis of X-ray diffraction line broadening. It is shown the thickness of the waveguide layer and the number of new crystalline phases depend not only on the temperature regime of the proton exchange, but also on the duration of post-exchange annealing. The simulation of the experimentally obtained curves of the diffraction reflection is carried out within the framework of the described model. As a result of the modeling, the depth of the waveguide layer was determined, which is consistent with the data obtained by the method of the mode spectroscopy. The models of the assumed profiles of the crystal lattice deformation caused by proton implantation are presented. The average values of the lattice microstrain and the phase composition of proton-exchange lithium niobate layers are determined.

Optical Properties Of Ion Exchanged And Swift Heavy Ion Beam Treated Silicate Glasses

Silver ion exchanges on silicate glasses were carried out at different temperatures 320 °C, 400 °C, and 500 °C for 60 min. The exchanged glasses were either annealed at 500 °C for 60 min or swift heavy ion (SHI) irradiated using 120 MeV Ag 9+ ions at a fluence of 5 x 10 12 ions/cm 2 . Silver nanoparticles were formed in the samples ion exchanged at 500 °C without any post- exchange treatments. Post-exchange annealing treatment resulted in silver nanoparticle formation for samples ion exchanged at temperature of 320 °C and 400 °C. Whereas post irradiation treatment for ion exchanged sample at 320 °C resulted in Ag4 nanocluster formation. After post-irradiation, the density of Ag nanoparticles increases for the sample ion exchanged at temperature of 500 °C. RBS was used to obtain silver depth profiles in the ion exchanged samples. Near surface accumulation of Ag atoms is observed in the RBS spectra for the samples prepared at high ion exchange temperature of 500 °C or SHI irradiated samples, in which Ag nanoparticle formation was also observed. UV-vis absorption spectroscopy and Transmission Electron Microscopy (TEM) were used to obtain signatures of nano-particles and to estimate their size. The ion exchanged glasses without nanoparticles were characterized for their possible use in multimode planar waveguides. The post-exchange treated glasses lost their waveguide property, but exhibited nonlinear optical property indicating their potential use for optical switching. Open aperture z-scan measurements for the sample prepared at high ion exchange temperature of 500 °C shows optical limiting behavior, whereas the samples prepared at low ion exchange temperature followed by annealing or irradiation show saturation behavior. Copyright © 2015 VBRI Press.

Proton-exchanged optical waveguides in LiTaO3: phase composition and stress

Planar optical waveguide layers were obtained in Z-cut LiTaO3 crystal substrates via proton exchange. Two different media were used as proton sources: benzoic acid melt and lithium hydrogensulphate vapors, controlling the thickness of the waveguides by duration and temperature of the proton exchange process and also by post-exchange annealing. The intrinsic stress caused by the penetration of the hydrogen ions into the crystal lattice was estimated by the optical integral method. The phase composition of proton-exchanged layers was analyzed based on the mode and IR-absorption spectra. An attempt to relate the level of stress to the level of proton doping has been made.

Nano-composite soda lime silicate glass prepared using silver ion exchange

Commercial soda lime silicate glasses have been subjected to ion exchange at different temperatures ranging from 320 to 500 °C in a molten mixture of AgNO3 and NaNO3 with molar ratio of 10:90, 02:98 and 50:50 for different time periods ranging from 40 to 180 min. Optical and structural properties of the ion exchanged glass are measured using UV–Vis–NIR absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy, fluorescence spectroscopy and transmission electron microscopy (TEM). Signature of silver nanoparticle formation is obtained from the UV–Vis–NIR spectra, which shows a peak at 425 nm due to surface plasmon resonance (SPR). Replacement of Na+ ions by Ag+ ions is inferred from FTIR spectra. Fluorescence spectra reveal the formation of Ag0 atoms from Ag+ ions at higher temperatures. TEM image shows the silver nanoparticles of average size 3.75 nm. At exchange temperature of 500 °C Ag nanoparticles are formed without post-exchange annealing treatment.

Channel optical waveguides in various silicate glasses—optimalization of their parameters

Channel optical waveguides were fabricated in silicate glasses of various types, i.e. soda–lime, boro-silicate and, especially, in the newly designed ZnO–SiO2 glasses containing Er2O3 and Yb2O3 via Ag+⇔Na+ and K+⇔Na+ ion exchanges. Optimalization of the fabrication conditions (ion exchange, post-exchange annealing) in the particular glasses was done in order to obtain channel waveguides whose parameters would resemble those of the commonly used optical fibres (single-mode at 1550 nm) so that the channel waveguide-fibre coupling of high efficiency would be provided. Attention was paid to the shape of optical field of these waveguides characterized by Near Field Imaging Method at 1500–1640 nm.

Optical waveguides fabricated by transition element ions exchange in some commercial and special optical glasses

We present a fabrication and properties study of planar optical waveguides fabricated in a variety of commercially available as well as non-commercial special silicate-based optical glasses. The exchanged ions coming from external sources were Ag+, Cu+, Cu2+ and Er3+. The reduction of Ag+ to Ag0 from which the high optical losses of waveguides may originate was strongly enhanced when the glass contained reducing fining agents as As2O3 or Sb2O3. The Cu2+ ion-exchange proceeded very quickly and resulted in the fabrication of waveguides with negligible birefringence. The samples containing exclusively Cu+ exhibited very strong blue–green luminescence even in the cases of very low copper content in the exchanged surface layers. The purely thermal erbium ion-exchange was successful only in lithium containing glasses; when using the electric-field-assisted ion-exchange the erbium containing waveguides were fabricated also in several sodium-rich and sodium–potassium glasses. The shallow erbium-containing surface layers were deepened by the post-exchange annealing of the as-exchanged samples. The properties of the fabricated waveguides are discussed from the point of view of the composition of substrate glasses, taking into account the ratios of the bridging and non-bridging oxygen atoms in the glass matrices and the presence of fining agents.

Annealed proton exchanged optical waveguides in lithium niobate: differences between the X- and Z-cuts

Abstract This article summarizes results and assessments of our systematic fabrication and characterization of proton exchanged (PE) and annealed proton exchanged (APE) waveguides study in lithium niobate. This study focused on different behavior of crystallographically diverse X(1 1 2 0) and Z(0 0 0 1) substrate cuts during waveguides fabrication, and differences in characteristics of the resulting waveguides. Non-toxic adipic acid was used as a proton source, and the waveguides properties were defined by a mode spectroscopy (waveguides characteristics) and neutron depth profiling (NDP, lithium concentration and distribution), infrared vibration spectra and elastic recoil detection analysis (ERDA, concentration and depth distribution of hydrogen). It was discovered that the X-cuts structure is more permeable for moving particles (lithium and hydrogen ions), which leads to a higher effectiveness of the PE process within the X-cut. The explanation of this phenomenon is based on the fitting X-cuts orientation towards cleavage planes of lithium niobate crystal. Higher content of interstitial hydrogen in the X-cuts then prevents lithium from free movement during the post-exchange annealing in direction to the surface of samples, and so causes a typical step-like shape of the depth concentration profiles of lithium within the X-cuts. A free transport of lithium within the Z-cuts is being reflected in a gradient shape of the lithium depth concentration profiles and extraordinary refractive index, as well the last but not least, in a trouble-free good reproducibility of the waveguides fabrication within the Z-cuts.

The possibility of tailoring the ne vs cLi relationship in lithium niobate optical waveguides

We present results of our study of concentration profiles of lithium ( c Li) in annealed proton exchanged (APE) waveguiding layers as measured by the neutron depth profiling (NDP) method. This non-destructive method, based on the 6Li(n,α) 3H reaction induced by thermal neutrons, allowed easy monitoring of c Li profiles in a large number of samples fabricated under various fabrication conditions. Our systematic study revealed that, though every particular waveguide could be characterised by very similar mirror-shaped extraordinary refractive index ( n e) as well as c Li depth profiles, in contrast with up to now generally accepted opinion, there was no linear relationship which unambiguously attributed Δn e to Δc Li. The most important fabrication step appeared to be the post-exchange annealing, during which the lithium atoms were transported towards the sample surfaces. The annealing regime pre-destined not only the depth distribution of the lithium atoms but, as a consequence of it, also other properties of the waveguiding region. That knowledge allows us to fabricate the APE waveguides with a priori given properties for a wide range of special applications. We have also formulated the n e vs c Li semi-empirical relationship, which was proved to fit all our fabricated APE waveguides.

Dependences of the refractive indices on the proton concentration in H:LiNbO3 waveguides

Proton-exchanged optical waveguides in lithium niobate crystals exhibit a rich variety of structures and phases. It is established that seven HxLi1−xNbO3 crystalline phases with a lithium niobate structure may form under various conditions of proton exchange and post-exchange annealing. A method is proposed to determine the proton concentration in the various phases identified. Relationships are established between the structural parameters, the proton concentration, and the ordinary and extraordinary refractive indices of various HxLi1−xNbO3 crystalline phases. The results can explain various optical phenomena observed in proton-exchanged waveguides and permit prediction of the characteristics of light-guide structures.

Effect of crystal phases on refractive index profiles of annealed proton-exchanged waveguides in X-cut LiTaO3

A complete structural phase diagram of annealed proton-exchanged X-cut LiTaO3 is presented, to relate refractive index change to proton-induced lattice deformation. From this diagram, explanations for the previously observed phenomena of index increase upon annealing and index decrease with increasing proton concentration (above a certain value) are derived. We have analyzed the evolution of index profiles during postexchange annealing, describing how the presence of multiple phases within a waveguide can lead to large index variations and buried index profiles. Finally, we identify at least two high-concentration phases that exhibit large temporal instabilities.

Velocity and attenuation of surface acoustic waves in proton-exchanged 128 degrees -rotated Y-cut LiNbO3

The velocity and attenuation of surface acoustic waves (SAW) in a 128 degrees -rotated Y-cut lithium niobate crystal with a proton-exchanged optical waveguiding layer on its surface have been studied. The measurements were carried out using the acoustic-optical diffraction method in the SAW frequency range 30-600 MHz. The SAW propagation was mainly along the X axis, though some velocity measurements were carried out for the normal direction. Strong velocity decrease and attenuation increase due to the proton exchange were observed. The acoustic dispersion and losses grow with the waveguide depth and SAW frequency, and are strongly affected by the post-exchange annealing. The results are explained by the formation of a HxLi1-xNbO3 layer on the LiNbO3 with many defects.

Changes of surface-acoustic-wave velocity on z-cut LiTaO 3 substrate by proton exchange and post-exchange annealing

The velocity of leaky surface-acoustic-waves (LSAWs) on proton-exchanged and annealed proton-exchanged Z-cut LiTaO3 substrates was measured by line-focus-beam (LFB) acoustic microscopy. It is revealed that the LSAW velocity is decreased from 3220 to 3000 m/s by the proton exchange and that the post-exchange annealing gives some recovery to the decreased velocity.

Proton-exchanged LiNbO/sub 3/ waveguides: the effects of post-exchange annealing and buffered melts as determined by infrared spectroscopy, optical waveguide measurements, and hydrogen isotopic exchange reactions

Infrared spectroscopy in the OH stretching region has been used to determine the extent of proton exchange in x- and z-cut lithium niobate as a function of temperature and time. The behavior observed is consistent with the occurrence of a diffusion-limited process within LiNbO/sub 3/. Apparent activation energies for the process determined from infrared spectroscopic measurements are consistent with the existence of a minimum exchange temperature and show that a relationship exists between waveguide depth and absorption band area. The measurements are also shown that hydrogen-bonded OH is substantially removed by annealing and that the extent of its formation is reduced by using buffered (lithium benzoate/benzoic acid) melts. It is suggested that hydrogen-bonded OH groups are responsible for many of the problems associated with proton-exchanged waveguides. Therefore, implementation of either annealing or buffered melts as part of the fabrication process is required to realize good-quality proton-exchanged waveguides.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>