Special Issue "Lithium Niobate: Bulk Crystals, Composites, Thin Films and Nanocrystals"

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Crystal Engineering".

Deadline for manuscript submissions: closed (15 April 2018)

Special Issue Editors

Guest Editor
Prof. Dr. Mirco Imlau

School of Physics, Universitat Osnabruck, Osnabruck, Germany
Website | E-Mail
Guest Editor
Prof. Dr. László Kovács

Wigner Research Centre for Physics, Hungarian Academy of Sciences, H-1121 Budapest, Konkoly-Thege M. út 29-33, Hungary
Website | E-Mail

Special Issue Information

Dear Colleagues,

The era of nanoscience has broadened our scientific cognition of lithium niobate (LN) crystals, revealing fascinating routes for their preparation as thin films, ultrathin membranes, nanoparticles,
nano-patterned surfaces, hybrid systems in combination with silica, polymers or liquid crystals, and many more. Moreover, technologies for precise structuring of the surface or the bulk on the sub-micron length scale using photons, electrons and ions have been successfully applied to LN. This progress is accompanied with an extension of our knowledge on LN from a nano-scientific viewpoint, i.e., on a microscopic level. It also opened the range of applications of LN in the direction of biophysics and medicine (cell-imaging and cancer therapy), photovoltaics of nano-ferroelectrics, integrated quantum photonics, nanophotonics, etc. This progress developed on the top of the already existing impact of bulk LN crystals, e.g., in the fields of nonlinear photonics (THz generation, frequency conversion), integrated optics (waveguiding, division wavelength multiplexing) or GHz-wave technologies (surface-acoustic wave detection, electro-optical modulators), etc.

This Special Issue intends to bring together the LN community around the latest experimental, theoretical and computational research highlights and may represent a state-of-the-art meeting point for researchers from diverse disciplines (physics, chemistry, nanotechnology, biophysics, material scientists, etc.) with the goal to disseminate the state-of-the-art knowledge on LN to a worldwide community and to foster the research progress on LN in nanosciences. We therefore would like to open this Special Issue to all related fields:

  • Nanosciences and -technologies

  • (Nonlinear) nanophotonics

  • Integrated optics

  • Quantum photonics

  • (Nano-)Biophotonics

  • Photovoltaics of nanoferroelectrics

  • Accelerator physics

Covering LN as:

  • Ultrathin LN-films

  • LN membranes

  • LN hybrid materials (LN/liquid crystals, LN/polymers, etc.)

  • LN on insulators

  • LN surfaces

  • 2D and 3D structured LN

  • LN nanocrystals and nanopowders

In addition to novel research results on bulk LN and its well-established applications.

Prof. Dr. Mirco Imlau
Prof. Dr. László Kovács
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Crystals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1200 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Lithium niobate;

  • Nano-scaled Oxides,

  • Niobate Nanoparticles and -crystals,
    ferroelectric photovoltaics

  • Lithium niobate nanophotonics.

Published Papers (12 papers)

View options order results:
result details:
Displaying articles 1-12
Export citation of selected articles as:

Research

Jump to: Review

Open AccessArticle Photorefractive Properties of Molybdenum and Hafnium Co-Doped LiNbO3 Crystals
Crystals 2018, 8(8), 322; https://doi.org/10.3390/cryst8080322
Received: 10 July 2018 / Revised: 8 August 2018 / Accepted: 10 August 2018 / Published: 13 August 2018
PDF Full-text (2610 KB) | HTML Full-text | XML Full-text
Abstract
A series of LiNbO3: Mo, Hf crystals with 0.5 mol % fixed MoO3 and various HfO2 concentrations (0.0, 2.0, and 3.5 mol %) were grown by the Czochralski technique. The photorefractive properties of the LiNbO3: Mo, Hf
[...] Read more.
A series of LiNbO3: Mo, Hf crystals with 0.5 mol % fixed MoO3 and various HfO2 concentrations (0.0, 2.0, and 3.5 mol %) were grown by the Czochralski technique. The photorefractive properties of the LiNbO3: Mo, Hf crystals were investigated by two-wave coupling measurements and the beam distortion method was employed to obtain the optical damage resistance ability. The UV-visible and OH absorption spectra were also studied. The experimental results imply that the photorefractive properties of LiNbO3: Mo crystals at laser wavelengths of 532, 488, and 442 nm can be greatly enhanced by doping HfO2 over the threshold concentration. At 442 nm especially, the response time of LN: Mo, Hf3.5 can be shortened to 0.9 s with a diffraction efficiency of 46.07% and a photorefractive sensitivity reaching 6.28 cm/J. Besides this, the optical damage resistance at 532 nm is 3 orders of magnitude higher than that of the mono-doped LiNbO3: Mo crystal, which is beneficial for applying it in the field of high-intensity lasers. Full article
Figures

Figure 1

Open AccessArticle Simultaneous Generation of Two Orthogonally Polarized Terahertz Waves by Stimulated Polariton Scattering with a Periodically Poled LiNbO3 Crystal
Crystals 2018, 8(8), 304; https://doi.org/10.3390/cryst8080304
Received: 7 April 2018 / Revised: 20 July 2018 / Accepted: 20 July 2018 / Published: 24 July 2018
PDF Full-text (1654 KB) | HTML Full-text | XML Full-text
Abstract
We present a theoretical investigation of the simultaneous generation of two orthogonally polarized terahertz (THz) waves by stimulated polariton scattering (SPS) with a periodically poled LiNbO3 (PPLN) crystal. The two orthogonally polarized THz waves are generated from SPS with A1 and
[...] Read more.
We present a theoretical investigation of the simultaneous generation of two orthogonally polarized terahertz (THz) waves by stimulated polariton scattering (SPS) with a periodically poled LiNbO3 (PPLN) crystal. The two orthogonally polarized THz waves are generated from SPS with A1 and E symmetric transverse optical (TO) modes in a LiNbO3 crystal, respectively. The parallel polarized THz wave is generated from A1 symmetric TO modes with type-0 phase-matching of e = e + e, and the perpendicular polarized THz wave is generated from E symmetric TO modes with type-I phase-matching of e = o + o. The two types of phase-matching of e = e + e and e = o + o can be almost satisfied simultaneously by accurately selecting the poling period of the PPLN crystal. We calculate the photon flux density of the two orthogonally polarized THz waves by solving the coupled wave equations. The calculation results indicate that the two orthogonally polarized THz waves can be efficiently generated, and the relative intensities between the two orthogonally polarized THz waves can be modulated. Full article
Figures

Figure 1

Open AccessArticle Small Polaron Hopping in Fe:LiNbO3 as a Function of Temperature and Composition
Crystals 2018, 8(7), 294; https://doi.org/10.3390/cryst8070294
Received: 11 June 2018 / Revised: 12 July 2018 / Accepted: 13 July 2018 / Published: 18 July 2018
PDF Full-text (911 KB) | HTML Full-text | XML Full-text
Abstract
Small-polaron hopping involved in charge transport in Fe-doped congruent lithium niobate is investigated as a function of temperature and composition by means of light-induced transient absorption spectroscopy. The relaxation dynamics of the light-induced polaron population is characterized by individual activation energies within different
[...] Read more.
Small-polaron hopping involved in charge transport in Fe-doped congruent lithium niobate is investigated as a function of temperature and composition by means of light-induced transient absorption spectroscopy. The relaxation dynamics of the light-induced polaron population is characterized by individual activation energies within different temperature ranges. A numerical investigation carried out by Monte Carlo simulations reveals that these findings may be understood in terms of the varying abundance of the different types of hops that the polarons may perform among regular or defective lattice sites. The role of the temperature and of the sample composition on the distribution of the different hop types is thus explored for a wide range of parameters, allowing one to preview the charge transport properties for a given set of experimental conditions. Full article
Figures

Figure 1

Open AccessArticle Polaron-Mediated Luminescence in Lithium Niobate and Lithium Tantalate and Its Domain Contrast
Crystals 2018, 8(5), 214; https://doi.org/10.3390/cryst8050214
Received: 6 April 2018 / Revised: 27 April 2018 / Accepted: 29 April 2018 / Published: 15 May 2018
PDF Full-text (3005 KB) | HTML Full-text | XML Full-text
Abstract
In this review article, we discuss photoluminescence phenomena mediated by polarons in lithium niobate (LNO). At first we present the fundamentals on polaron states in LNO and their energy levels, i.e., on free and bound electron polarons, on hole polarons as well as
[...] Read more.
In this review article, we discuss photoluminescence phenomena mediated by polarons in lithium niobate (LNO). At first we present the fundamentals on polaron states in LNO and their energy levels, i.e., on free and bound electron polarons, on hole polarons as well as on bipolarons. We discuss the absorption measurements on reduced as well as on doped LNO that made the characterization of the formed polaron states possible by their absorption bands. Next, we proceed by reporting on the two polaron-mediated photoluminescence bands that have been observed in LNO: (1) A near-infrared luminescence band in the range of 1.5 eV shows a mono-exponential decay and a strong dependence on iron doping. This luminescence is emitted by bound polarons returning from an excited state to the ground state. (2) A luminescence band at visible wavelengths with a maximum at 2.6 eV shows a stretched-exponential decay and is strongly enhanced by optical damage resistant doping around the doping threshold. This luminescence stems from the recombination of free electron and hole polarons. The next major topic of this review are domain contrasts of the visible photoluminescence that have been observed after electrical poling of the substrate, as singly inverted domains show a slightly reduced and faster decaying luminescence. Subsequent annealing results in an exponential decrease of that domain contrast. We show that this contrast decay is strongly related to the mobility of lithium ions, thus confirming the role of polar defect complexes, including lithium vacancies, for these domain contrasts. Finally we discuss the extension of our investigations to lithium tantalate (LTO) samples. While the results on the domain contrast and its decay are similar to LNO, there are remarkable differences in their luminescence spectra. Full article
Figures

Figure 1

Open AccessArticle Lattice Parameters of Optical Damage Resistant In-Doped LiNbO3 Crystals
Crystals 2018, 8(5), 210; https://doi.org/10.3390/cryst8050210
Received: 17 April 2018 / Revised: 2 May 2018 / Accepted: 3 May 2018 / Published: 13 May 2018
Cited by 1 | PDF Full-text (567 KB) | HTML Full-text | XML Full-text
Abstract
The lattice parameters in optical damage resistant crystal LiNbO3-In were measured for the first time using the X-ray powder method with an internal standard, which provides a high accuracy of the results. The lattice parameters vs. In concentration were obtained in
[...] Read more.
The lattice parameters in optical damage resistant crystal LiNbO3-In were measured for the first time using the X-ray powder method with an internal standard, which provides a high accuracy of the results. The lattice parameters vs. In concentration were obtained in the concentration range from 0.24 to 3.2 at % In in the crystal. The results are discussed in the framework of currently accepted model of the LiNbO3 intrinsic defect structure. Full article
Figures

Figure 1

Open AccessArticle Optical Absorption and Reflectivity of a Molecular Cluster of Lithium Niobate Adsorbed on a Graphene Layer
Crystals 2018, 8(5), 208; https://doi.org/10.3390/cryst8050208
Received: 15 April 2018 / Revised: 7 May 2018 / Accepted: 8 May 2018 / Published: 10 May 2018
PDF Full-text (1017 KB) | HTML Full-text | XML Full-text
Abstract
We used density functional theory to study the adsorption of a molecular cluster of lithium niobate (LiNbO3) on a graphene layer. The cluster size is about 1.2 nm, and it has 11 molecules. We optimized the cluster, and then we calculated
[...] Read more.
We used density functional theory to study the adsorption of a molecular cluster of lithium niobate (LiNbO3) on a graphene layer. The cluster size is about 1.2 nm, and it has 11 molecules. We optimized the cluster, and then we calculated its interaction with the optimized graphene layer. We found that the cluster is adsorbed on the graphene layer with an adsorption energy of −2.2213 eV (−0.068 eV/atom). Afterwards, we calculated the reflectivity, and the optical absorption coefficients of the system cluster-graphene and of a graphene layer alone, to make a comparison. We found large differences in the values of these properties of the new system, with respect to the corresponding ones of graphene. We performed our calculations using the general gradient approximation (GGA), and the GGA modified for van der Waals interactions in order to take into account the long-range correlations. Full article
Figures

Graphical abstract

Open AccessArticle Analysis of Waveguides on Lithium Niobate Thin Films
Crystals 2018, 8(5), 191; https://doi.org/10.3390/cryst8050191
Received: 5 April 2018 / Revised: 24 April 2018 / Accepted: 24 April 2018 / Published: 27 April 2018
PDF Full-text (2320 KB) | HTML Full-text | XML Full-text
Abstract
Waveguides formed by etching, proton-exchange (PE), and strip-loaded on single-crystal lithium niobate (LN) thin film were designed and simulated by a full-vectorial finite difference method. The single-mode condition, optical power distribution, and bending loss of these kinds of waveguides were studied and compared
[...] Read more.
Waveguides formed by etching, proton-exchange (PE), and strip-loaded on single-crystal lithium niobate (LN) thin film were designed and simulated by a full-vectorial finite difference method. The single-mode condition, optical power distribution, and bending loss of these kinds of waveguides were studied and compared systematically. For the PE waveguide, the optical power distributed in LN layer had negligible change with the increase of PE thickness. For the strip-loaded waveguide, the relationships between optical power distribution in LN layer and waveguide thickness were different for quasi-TE (q-TE) and quasi-TM (q-TM) modes. The bending loss would decrease with the increase of bending radius. There was a bending loss caused by the electromagnetic field leakage when the neff of q-TM waveguide was smaller than that of nearby TE planar waveguide. LN ridge waveguides possessed a low bending loss even at a relatively small bending radius. This study is helpful for the understanding of waveguide structures as well as for the optimization and the fabrication of high-density integrated optical components. Full article
Figures

Figure 1

Open AccessArticle Computer Modelling of Hafnium Doping in Lithium Niobate
Crystals 2018, 8(3), 123; https://doi.org/10.3390/cryst8030123
Received: 3 January 2018 / Revised: 28 February 2018 / Accepted: 1 March 2018 / Published: 6 March 2018
Cited by 1 | PDF Full-text (239 KB) | HTML Full-text | XML Full-text
Abstract
Lithium niobate (LiNbO3) is an important technological material with good electro-optic, acousto-optic, elasto-optic, piezoelectric and nonlinear properties. Doping LiNbO3 with hafnium (Hf) has been shown to improve the resistance of the material to optical damage. Computer modelling provides a useful
[...] Read more.
Lithium niobate (LiNbO3) is an important technological material with good electro-optic, acousto-optic, elasto-optic, piezoelectric and nonlinear properties. Doping LiNbO3 with hafnium (Hf) has been shown to improve the resistance of the material to optical damage. Computer modelling provides a useful means of determining the properties of doped and undoped LiNbO3, including its defect chemistry, and the effect of doping on the structure. In this paper, Hf-doped LiNbO3 has been modelled, and the final defect configurations are found to be consistent with experimental results. Full article
Open AccessArticle Structural and Magnetic Behavior of Oxidized and Reduced Fe Doped LiNbO3 Powders
Crystals 2018, 8(3), 108; https://doi.org/10.3390/cryst8030108
Received: 30 December 2017 / Revised: 31 January 2018 / Accepted: 6 February 2018 / Published: 26 February 2018
PDF Full-text (2856 KB) | HTML Full-text | XML Full-text
Abstract
Changes in structural and magnetic properties have been systematically induced in lithium niobate (LiNbO3) powders, Fe-doped with different concentrations and thermally treated in oxidized and reduced states. A rather strong ferromagnetic response at room temperature with a saturation magnetization of 0.96
[...] Read more.
Changes in structural and magnetic properties have been systematically induced in lithium niobate (LiNbO3) powders, Fe-doped with different concentrations and thermally treated in oxidized and reduced states. A rather strong ferromagnetic response at room temperature with a saturation magnetization of 0.96 Am2kg−1 was obtained for the higher utilized doping concentration, which is of the order of 1% mol. This may be considered a first report of the manifestation of ferromagnetism in nanocrystalline lithium niobate powders within the regime of very low Fe-doping concentrations. Post-thermal treatment in a controlled atmosphere is key for inducing and detecting this behavior, which can also be explained as the effective recombination of Fe impurities with oxygen vacancies in the surface of the material. Mechanochemical-calcination was employed for the synthesis of LiNbO3 powders and after that, a diffusion process of 0.44%, 0.89%, 1.47% and 2.20% mass of Fe2O3 was used in the Fe-doping. Oxidation and reduction processes were performed using a controlled atmosphere of ultra-high purity oxygen and hydrogen, respectively. X-ray diffraction and Raman spectroscopy were employed to characterize the materials. The magnetic properties were studied using Vibration Sample magnetometry and Electron Spin Resonance spectroscopy. Full article
Figures

Figure 1

Open AccessArticle Improvement in the Photorefractive Response Speed and Mechanism of Pure Congruent Lithium Niobate Crystals by Increasing the Polarization Current
Crystals 2017, 7(12), 368; https://doi.org/10.3390/cryst7120368
Received: 24 September 2017 / Revised: 4 November 2017 / Accepted: 7 December 2017 / Published: 11 December 2017
PDF Full-text (3704 KB) | HTML Full-text | XML Full-text
Abstract
A series of pure congruent lithium niobate (LiNbO3, CLN) crystals were grown and directly polarized under different electric currents in the growth furnace. Their holographic properties were investigated from the ultraviolet to the visible range. The response time shortened, whereas the
[...] Read more.
A series of pure congruent lithium niobate (LiNbO3, CLN) crystals were grown and directly polarized under different electric currents in the growth furnace. Their holographic properties were investigated from the ultraviolet to the visible range. The response time shortened, whereas the diffraction efficiency increased incrementally with the electric current. In particular, the response time of CLN polarized under 100 mA can be reduced by a factor of 10 with a still high saturation diffraction efficiency of about 40.8% at 351 nm. Moreover, its response speed improved by 60 times and 10 times for 473 and 532 nm laser, respectively. The light erasing behavior implies that at least two kinds of photorefractive centers exist in the crystals. Increasing the polarization current induces two pronounced UV absorption peaks and a wide visible absorption peak in CLN crystals. The diffusion effect dominates the photorefractive process and electrons are the dominant carriers. The possible mechanism for the fast photorefractive response is discussed. Increasing the polarization electric current is an effective method to improve the photorefractive response of LN crystal. Full article
Figures

Figure 1

Open AccessArticle Lattice Site of Rare-Earth Ions in Stoichiometric Lithium Niobate Probed by OH Vibrational Spectroscopy
Crystals 2017, 7(8), 230; https://doi.org/10.3390/cryst7080230
Received: 7 July 2017 / Revised: 20 July 2017 / Accepted: 21 July 2017 / Published: 25 July 2017
Cited by 2 | PDF Full-text (2293 KB) | HTML Full-text | XML Full-text
Abstract
Rare-earth (RE = Er3+, Nd3+, or Yb3+) ion-doped stoichiometric LiNbO3 crystals were grown by the Czochralski and the high-temperature top-seeded solution growth methods. For the 0.22–0.87 mol% concentration range of the RE oxides in the melt/solution,
[...] Read more.
Rare-earth (RE = Er3+, Nd3+, or Yb3+) ion-doped stoichiometric LiNbO3 crystals were grown by the Czochralski and the high-temperature top-seeded solution growth methods. For the 0.22–0.87 mol% concentration range of the RE oxides in the melt/solution, in addition to the well-known hydroxyl (OH) vibrational band in undoped stoichiometric LiNbO3, a new infrared absorption band was observed at about 3500 cm−1, similar to the case of the trivalent optical damage resistant (ODR) dopants In3+ and Sc3+. By comparing the frequencies and polarization dependences of the bands to those detected for ODR ion containing crystals, they are attributed to the stretching vibration of OH ions in RE3+Nb-OH complexes. Consequently, above a given concentration threshold, some of the rare-earth ions are assumed to occupy niobium sites in the LiNbO3 lattice. The same model is also suggested for RE-doped congruent LiNbO3 crystals containing over-threshold (>5 mol %) amounts of the Mg-co-dopant. Full article
Figures

Figure 1

Review

Jump to: Research

Open AccessReview Recent Achievements on Photovoltaic Optoelectronic Tweezers Based on Lithium Niobate
Crystals 2018, 8(2), 65; https://doi.org/10.3390/cryst8020065
Received: 22 December 2017 / Revised: 22 January 2018 / Accepted: 24 January 2018 / Published: 30 January 2018
Cited by 1 | PDF Full-text (4992 KB) | HTML Full-text | XML Full-text
Abstract
This review presents an up-dated summary of the fundamentals and applications of optoelectronic photovoltaic tweezers for trapping and manipulation of nano-objects on the surface of lithium niobate crystals. It extends the contents of previous reviews to cover new topics and developments which have
[...] Read more.
This review presents an up-dated summary of the fundamentals and applications of optoelectronic photovoltaic tweezers for trapping and manipulation of nano-objects on the surface of lithium niobate crystals. It extends the contents of previous reviews to cover new topics and developments which have emerged in recent years and are marking the trends for future research. Regarding the theoretical description of photovoltaic tweezers, detailed simulations of the electrophoretic and dielectrophoretic forces acting on different crystal configurations are discussed in relation to the structure of the obtained trapping patterns. As for the experimental work, we will pay attention to the manipulation and patterning of micro-and nanoparticles that has experimented an outstanding progress and relevant applications have been reported. An additional focus is now laid on recent work about micro-droplets, which is a central topic in microfluidics and optofluidics. New developments in biology and biomedicine also constitute a relevant part of the review. Finally, some topics partially related with photovoltaic tweezers and a discussion on future prospects and challenges are included. Full article
Figures

Figure 1

Back to Top