Doped LiNbO3 Research Articles

Emission characteristics, crystalline phase and composition of Er3+/Yb3+ doped LiNbO3 thin films deposited by e-beam evaporation

Er3+/Yb3+ doped LiNbO3 (LN) single crystal films with varying Yb3+ doping level were grown on z-cut LiTaO3 bulk single crystals via using e-beam evaporation method. The crystallographic orientation, elemental distribution, fluorescence properties, ionic valence states, Er3+ concentration, Yb3+ concentration and Li2O content of films were carefully studied. Results from XRD, SEM and Raman scattering conclude that the predominant phase of these films is LN and they are oriented along (006). The results of energy dispersive spectroscopy indicate that constituent elements are uniformly distributed over the entirety of the films. The visible and near-infrared luminescence intensities rise with increasing Yb3+-doping concentration. The Li2O content of films remains constant at 48.8 mol% with growing Yb3+-doping level based on the optical birefringence method, which is consistent with the Raman results. XPS results suggest that the Er3+ and Yb3+ concentrations in the films are lower than that in the polycrystalline powder since e-beam evaporation has a low efficiency of heavy Er3+ and Yb3+ ions.

Mechanosynthesis, Structure and Photoluminescent Properties of the Pr3+ Doped LiNbO3, LiNbO3:Mg, LiTaO3 Nanopowders

In the current work, nanocrystalline powders with different compositions, namely Li0.98Pr0.02NbO3, Li0.93Pr0.02Mg0.05NbO3 and Li0.98Pr0.02TaO3 were synthesized for the first time using the method of high-energy ball milling of the starting materials (Li2CO3, Nb2O5, Ta2O5, MgO, Pr6O11), followed by high-temperature annealing. XRD data analysis confirmed the absence of parasitic phases in the obtained nanocrystalline compounds. The estimated particle sizes ranged from 20 to 80 nm. From the obtained nanopowders, ceramic samples were prepared using specially developed equipment, which allowed for pressing at elevated temperatures with a simultaneous application of a constant electric field. The obtained photoluminescence spectra exhibit characteristic features of Pr3+ ions in the crystal structure of LiNbO3 and LiTaO3 and are most efficiently excited by UV light. Samples pressed with an electric field application show higher intensity of photoluminescence. Investigations of the temperature dependence of electrical conductivity of the Li0.98Pr0.02NbO3 sample, pressed with the application of an electric field, indicate that the conductivity mechanism is similar to that of LiNbO3 single crystals and, at high temperatures, is attributed to the lithium conduction mechanism.

Structure and spectroscopic properties of Er3+ doped LiNbO3 thin film grown by e-beam evaporation

Er3+ doped LiNbO3 (Er: LN) single crystal films with varied doping levels of Er3+ were grown on z-cut LiTaO3 bulk single crystals by using e-beam evaporation method. The crystallographic orientation, fluorescence properties, ions valence states, Er3+ concentration and Li2O content of films were studied. The main phase of the obtained films is determined to be LN from X-ray diffraction and Raman scattering studies, and the films are found to be orienting along (006). Enhancement in the visible and near-infrared luminescence is observed as the doping concentration of Er3+ is increased. The Li2O content of films is determined using the optical birefringence method and found to be at a constant value of 48.8 mol%, which is consistent with the Raman results. XPS results show that the Er concentration in the films is lower than that in the polycrystalline powder since e-beam evaporation has a low efficiency for heavier Er3+. Fluorescence intensity ratios estimated at different measurement temperatures suggest that the Er: LN films have excellent temperature sensitivity, which shows the potential of the films for optical thermometry applications.

Electronic and optical properties of Au and Ag doped LiNbO3 from first principles study

Using the first-principles calculation, the electronic and optical properties of Ag and Au doped LiNbO3 are investigated. The first-principles calculation in this work is implemented using CASTEP computer code with GGA-PBE exchange–correlation. The calculated band gap of pure LiNbO3 was observed at 3.547 eV and for doped LiNbO3, the band gap shows a reduction in the band gap value. For Au-doped LiNbO3 shows a value of 1.120 eV while Ag-doped LiNbO3 give a band gap of 0.708 eV. The density of states is calculated to analyze the effect of Au and Ag doping on the electronic properties and absorption spectra. The results show a significant shift toward visible region in the optical absorption edge of Au and Ag doped LiNbO3 compared to pure LiNbO3. The dielectric constant for pure and doped structures are calculated. The enhancement in optical absorption of Ag and Au doped LiNbO3 making it a promising material for photovoltaic and photocatalyst application.

J-V characteristics of sol-gel-prepared Zn2+ doped LiNbO3

Herein, a stable LiNbO3 (LN) sol, with different Zn2+ contents, is prepared using ethanol niobium, lithium acetate and zinc acetate as starting materials, absolute ethanol as a solvent, and acrylic acid and benzoyl acetone (BzAcH) as additives. The influence of Zn2+ content on LN crystal structure, light transmittance and J-V curve characteristics is studied in detail. XRD results reveal that Zn2+ doping, with a molar content of less than 5%, does not influence the crystal structure of LN. SEM indicates that the grain size of LN films gradually increases with the increase of doping content. The surface quality of LN films becomes worse when the doping content of Zn2+ reaches 5%. Moreover, light transmittance tests show that the maximum light transmittance is attained at the doping amount of 3%. J-V curves demonstrate that Pt/LN/LNO(LaNiO3) structure shows excellent resistance switching (RS) effect due to the formation of Schottky barrier at the Pt/LN interface, which initially becomes prominent with the increase of Zn2+ content, followed by a gradual decrease. On the other hand, In/LN/LNO structure exhibits poor RS effect due to the unobvious Schottky barrier at In/LNO interface. Furthermore, J-V curves at different temperatures demonstrate that the RS effect of Pt/LN/LNO structure tends to deteriorate, while the refractive index of LN film increases with the decrease of temperature. Herein, the abovementioned RS phenomenon is analyzed and explained in terms of the relationship between interfacial barrier and doping amount of Zn2+, migration of oxygen vacancies, and the relationship between insulation property of LN films and temperature. The research results are of experimental and theoretical significance for practical applications of LN films.

13-21

Raman spectroscopy, laser conoscopy and photoinduced light scattering methods have been applied to comparatively study composition uniformity of strongly doped LiNbO3 crystals with a magnesium concentration close to a threshold value ≈5 mol% MgО, grown from a charge synthesized using precursor Nb2O5:Mg (homogeneous doping method) and at direct addition of magnesium to the melt (direct doping method). It has been shown that application of homogeneous doping method allows one to obtain compositionally more homogeneous heavily doped LiNbO3:Mg crystal than direct melt doping method.

Влияние способа сильного легирования на композиционную однородность и оптические свойства монокристаллов LiNbO-=SUB=-3-=/SUB=- : Mg

Raman spectroscopy, laser conoscopy and photoinduced light scattering methods have been applied to comparatively study composition uniformity of strongly doped LiNbO3 crystals with a magnesium concentration close to a threshold value ≈5 mol% MgО, grown from a charge synthesized using precursor Nb2O5:Mg (homogeneous doping method) and at direct addition of magnesium to the melt (direct doping method). It has been shown that application of homogeneous doping method allows one to obtain compositionally more homogeneous heavily doped LiNbO3:Mg crystal than direct melt doping method.

State of the Art in Crystallization of LiNbO3 and Their Applications

Lithium niobate (LiNbO3) crystals are important dielectric and ferroelectric materials, which are widely used in acoustics, optic, and optoelectrical devices. The physical and chemical properties of LiNbO3 are dependent on microstructures, defects, compositions, and dimensions. In this review, we first discussed the crystal and defect structures of LiNbO3, then the crystallization of LiNbO3 single crystal, and the measuring methods of Li content were introduced to reveal reason of growing congruent LiNbO3 and variable Li/Nb ratios. Afterwards, this review provides a summary about traditional and non-traditional applications of LiNbO3 crystals. The development of rare earth doped LiNbO3 used in illumination, and fluorescence temperature sensing was reviewed. In addition to radio-frequency applications, surface acoustic wave devices applied in high temperature sensor and solid-state physics were discussed. Thanks to its properties of spontaneous ferroelectric polarization, and high chemical stability, LiNbO3 crystals showed enhanced performances in photoelectric detection, electrocatalysis, and battery. Furthermore, domain engineering, memristors, sensors, and harvesters with the use of LiNbO3 crystals were formulated. The review is concluded with an outlook of challenges and potential payoff for finding novel LiNbO3 applications.

Дефекты и некоторые физические свойства номинально чистых и легированных цинком кристаллов ниобата лития

The features of defect structure and their influence on the properties of LiNbO3:Zn crystals, doped in a wide concentration range, including two concentration thresholds (at ~ 3.0 and ~ 6.8 mol. % ZnO in the melt), were studied by absorption IR spectroscopy in the region of OH--group valence vibrations, photoluminescence in the visible region of the spectrum, and photoinduced light scattering. In LiNbO3:Zn(0.004-2.01 mol. % ZnO) crystals the increase of zinc concentration led to increasing in the OH--group concentration and decreasing the luminescence intensity of luminescence centers associated with NbLi defects. Apparently, the latter was connected with the formation of small energy levels near the bottom of the conduction band as the zinc atoms displaced niobium atoms from the lithium positions in the ideal structure and the NbLi defect concentration decreased, respectively. In highly doped LiNbO3:Zn crystals (4.46-6.5 mol. % ZnO) and in the LiNbO3stoich(6.0 wt. % K2O) crystal there were lower OH--group concentration, the increase of band gap by 0.3-0.4 eV, and the increase of luminescence intensity in the green region of the spectrum due to the formation of new recombination channels compared to weakly doped crystals. In addition, in such crystals, the increase of proton conductivity was observed due to increasing in the concentration of interstitial hydrogen H+ and, as a result, the formation of many small acceptor levels near the valence band.

Growth and properties of Pr3+ doped LiNbO3 crystal with Mg2+ incorporation: A potential material for quasi-parametric chirped pulse amplification

Praseodymium ion-doped LiNbO3 (Pr:LN) with x mol% Pr3+ ions (x = 0.5, 1, and 2) and praseodymium ion- and magnesium ion-co-doped LiNbO3 (Pr:Mg:LN) with 0.5 mol% Pr3+ and 5 mol% Mg2+ were grown by the Czochralski method. The contents of Pr3+ and Mg2+ in the crystals were measured by inductively coupled plasma optical emission spectrometer (ICP-OES). The Li/Nb values of the crystals were determined by Raman spectroscopy. X-ray diffraction(XRD) results showed that the structure of the doped crystals had no obvious change. The thermal properties of the crystals were investigated, and the results indicated that the thermal properties of LiNbO3 were more prominent than those of other crystals for quasi-parametric chirped pulse amplification (QPCPA). The optical properties of the crystals were studied systematically. The transmittance of the as-grown crystals at 1030 nm and 3000 nm reached over 68%, and there was a strong absorption peak at 1572 nm. Moreover, the laser damage threshold of the crystals was investigated, and the value of the Pr:Mg:LN crystal was as high as 47.3 MW/cm2 (@532 nm,10 ns). These characteristics of the as-grown crystals may provide promising applications in QPCPA.

P-Type conductivity mechanism and defect structure of nitrogen-doped LiNbO3 from first-principles calculations.

Most metal-doped lithium niobates (LiNbO3, LN) exhibit n-type conductivity. The absence of p-type conductive LiNbO3 limits its application. Based on the finding that p-type conductive LiNbO3 can be realized by doping with a non-metallic element N, we investigate the most stable defect configurations and formation energies of LiNbO3 doped with non-metal nitrogen (LN:N) by first-principles calculations. Nitrogen substitution, interstitial and quasi-substitution point defects in different sites and their effects were explored. The results show that N prefers to occupy the oxygen site with only little lattice distortion. Ab initio molecular dynamics (AIMD) simulations confirm the structural stability of an N ion occupying the O site. The charge-state transition level ε(0/-1) slightly above the valence band maximum (VBM) indicates that N point defects would contribute to p-type conductivity of LiNbO3. The analysis of the band structure reveals that the partially filled impurity levels can accommodate electrons that jump from valence bands and result in holes to become the main charge carriers. The calculation not only explains the occurrence of p-type conductivity in LN:N but also provides a simple and efficient way to discover p-type conductive candidates in numerous doped LiNbO3 crystals.

Dielectric properties and electrical conductivity of LiNbO3:Zn crystals in the temperature range 310–900 К

Electrical conductivity and dielectric constant have been researched in a series of crystals LiNbO3:Zn(~4.0–9.0 mol% ZnО in a melt) by application of constant voltage with a couple of electrodes (~<500 K) and impedance spectroscopy (~>500 К). In order to compare results we have also researched electrical conductivity σdc of congruent LiNbO3congr and magnesium doped LiNbO3:Mg crystals. We have established that electron contribution to electrical conductivity of doped crystals LiNbO3:Zn and LiNbO3:Mg is greatly smaller than that of a congruent crystal LiNbO3congr. A decrease in conductivity is apparently connected with a restructure of LiNbO3 crystals at high concentrations of magnesium and zinc. Doping of crystals with Zn leads to drastic changes not only in the electron conductivity area (T < 500 K), but also in a lithium ion conductivity area (Т > 500 K). At this, parameters of temperature dependence of lithium ion conductivity depend on both zinc concentration and crystallographic orientation of samples.

Impact of a Dopant Impurity Electronic Structure on Physical Properties, Defect Structure, and Features of Lithium Niobate Doping Technology

The macro- and microstructure of doped LiNbO3 crystals is studied, their transmission spectra are investigated, and the effective coefficients characterizing the dopant impurity distribution are determined. We analyze the literature data on phase diagrams of the ternary system Li2O–Nb2O5–dopant oxide and the electron configurations of dopant elements, and the results suggest that this can be used as a basis for designing technological conditions for growing doped lithium niobate crystals and predicting their quality. With p‑elements (boron), structurally and compositionally uniform LiNbO3 crystals can be grown, with the doping impurity not being incorporated in the crystal. s- and d-metals (magnesium and zinc) have a similar effect on the melt and properties of resulting LiNbO3 crystals, which have periodic domain structures and similar types of point defects. Due to their electronic structure, f-metals (cerium) bring the melt to such a structure that this enables the formation of a periodic domain structure in LiNbO3 crystals during their growth.

Optical Properties and Defects of Double Doped Crystals LiNbO3:Mg(5.05):Fe(0.009) and LiNbO3:Zn(4.34):Fe(0.02) (mol%)

Photoinduced light scattering, laser conoscopy, and IR spectroscopy in the absorption region of OH stretching vibrations are used to study photorefractive properties and compositional homogeneity of double doped (mol%) LiNbO3:Mg(5.05):Fe(0.009) and LiNbO3:Zn(4.34):Fe(0.02) crystals grown from a congruent melt. All frequencies in the IR spectrum of the LiNbO3:Mg(5.05):Fe(0.009) (mol%) crystal in the region of OH stretching vibrations are shifted to the high-frequency region compared with the spectrum of the nominally pure congruent crystal. This is caused by the absence of $$\rm{Nb}_{Li}^{4+}$$ point defects and the corresponding (VLi)–OH complex defects in the crystal structure and by the formation of new MgLi–MgNb–OH and MgLi–OH–FeNb complex defects. The LiNbO3:Zn(4.34):Fe(0.02) (mol%) crystal (zinc concentration is between threshold concentrations for ∼3.0 mol% and 7.0 mol% of ZnO) is found to be much more compositionally homogeneous than the LiNbO3:Mg(5.05):Fe(0.009) (mol%) crystal, despite much higher iron content in the former. This is explained by the fact that magnesium content in this crystal is close to the threshold concentration for ∼5.5 mol% of MgO. Neither of the crystals exhibits photoinduced light scattering.

Rapid response of photorefraction in vanadium and magnesium co-doped lithium niobate

Vanadium and magnesium co-doped LiNbO3 (LN) crystals were grown, and their photorefractive properties were studied in the visible spectral region. At 488 nm the shortest response time of 80 ms was achieved for an LN crystal co-doped with 0.1 mol% V2O5 and 6.0 mol% MgO, which is the more rapid than other reported doped LN crystals in the same wavelength region. The sensitivity of this crystal reaches 17 cm J−1 with an adequate diffraction efficiency of 4.0%. A schematic diagram for energy level is proposed and discussed. Through the analysis of defect structure and absorption spectra, we found that the change of the vanadium ions occupancy from Li sites to Nb sites is responsible for significant shortening the response time. The rapid response of vanadium and magnesium co-doped LN crystal can play an excellent role in the field of dynamic holography and practical holographic 3D-storage applications.

Near infrared mechanoluminescence from the Nd3+ doped perovskite LiNbO3:Nd3+ for stress sensors

Mechanoluminescence (ML) from most state-of-the-art phosphors primarily appears within the spectral range of ultraviolet to visible. Here, a novel near infrared ML which can penetrate tissues is achieved in Nd3+ doped LiNbO3.

Влияние электронного строения примеси на физические свойства, дефектную структуру и особенности технологии легирования кристаллов ниобата лития

Macro- and microstructure were researched for doped LiNbO3 crystals. The transmission spectra and the effective distribution coefficients of the dopant were studied. The analysis of literature data on ternary phase diagrams of systems Li2O-Nb2O5-dopant oxide and electronic configurations of dopants has revealed a possibility to predict technological growth conditions and quality of doped lithium niobate crystals. At this p-elements (boron) provide growth of structurally and compositionally uniform LiNbO3 crystals without incorporation of a dopant into the structure. Metals, s- and d-elements (magnesium and zinc) influence the melts and the crystal properties similar. At this non-periodical domain structures and similar types of point defects appear. Metals of f-elements (cerium) order the melt structure in such a way that provide forming of growth regular domain structure in LiNbO3 crystals due to their electron configurations. Keywords: crystal, lithium niobate, doping, optical microscopy.

Effect of Defects on Spontaneous Polarization in Pure and Doped LiNbO₃: First-Principles Calculations.

Numerous studies have indicated that intrinsic defects in lithium niobate (LN) dominate its physical properties. In an Nb-rich environment, the structure that consists of a niobium anti-site with four lithium vacancies is considered the most stable structure. Based on the density functional theory (DFT), the specific configuration of the four lithium vacancies of LN were explored. The results indicated the most stable structure consisted of two lithium vacancies as the first neighbors and the other two as the second nearest neighbors of Nb anti-site in pure LN, and a similar stable structure was found in the doped LN. We found that the defects dipole moment has no direct contribution to the crystal polarization. Spontaneous polarization is more likely due to the lattice distortion of the crystal. This was verified in the defects structure of Mg2+, Sc3+, and Zr4+ doped LN. The conclusion provides a new understanding about the relationship between defect clusters and crystal polarization.

Piezophotonic effect based on mechanoluminescent materials for advanced flexible optoelectronic applications

Recently, there has been an increasing research interest in the emerging fields of piezophotonics, which is the great interesting physics responsible for numbers of important technologies such as light source, smart sensor and mechanoelectronics. Piezophotonic effect is the coupling between the piezoelectric polarization and the photonic excitation in crystal that has a non-central symmetry. The strain-induced piezopotential can stimuli the photon emission without additional energy excitation such as light and electricity, which also offers great new opportunities of manipulating and fabrication of flexible optoelectronic devices. In this review, we will give a detailed description of the piezophotonic effect including its theoretical fundamental and practical applications. The piezophotonic light emission in doped ZnS CaZnOS, SrAl2O4 and LiNbO3 attract great interesting during the past years, and researchers have executed many scientific inquiries into flexible/stretchable optoelectronic devices. Until now, significant breakthroughs have been achieved on piezophotonic e-signature system, visible wearable electronic devices and multi-physical coupling devices. Certainly, rapid innovations in this field will be quite significant to the future of human life.

Self-Induced Second-Harmonic and Sum-Frequency Generation from Interfacial Engineered Er3+/Fe3+ Doped LiNbO3 Single Crystal via Femtosecond Laser Ablation

An interfacial engineered 1 mol % Er3+ and 0.07 mol % Fe3+ doped LiNbO3 single crystal was prepared by processing its surface into periodic rectangular arrays under femtosecond laser ablation. We demonstrated effective self-induced second-harmonic and sum-frequency generation emission peaks at 391, 487, 582, and 762 nm excited by a continuous wave laser at 980 nm, which were accompanied by the typical upconversion spectrum. Significant scattering and localization effects were analyzed as two main factors that contributed to the second-harmonic and sum-frequency generations. In addition to these observations, nanosecond second-harmonic laser emission peaks centered at 534.6 and 532.0 nm with a full width at half-maximum of approximately 0.77 nm were also generated under nanosecond laser illumination at 1064 nm. The obvious laser mode competition between these two emission peaks was investigated, and finally, the peak at 532.0 nm won with the increase of the pumping laser energy. These findings may play a v...