Electronic structure of deep centers in LiNbO3

Akhmadullin, I. Sh.; Golenishchev-Kutuzov, V. A.; Migachev, S. A.

doi:10.1134/1.1130478

Cited by 32 publications

(19 citation statements)

References 20 publications

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“…However after annealing at 500 °C the band with the maximum at 500-520 nm is predominant. It is necessary to note that authors in [15] have also observed the similar difference in spectra after reducing annealing of thin LN plates in vacuum. After annealing at 700 °C the absorption in the short-wave region prevails in an area, which is adjacent to the sample surface.…”

Section: Annealing In Hmentioning

confidence: 95%

Spatial distribution of LiNbO₃single crystals optical properties changes after redox high-temperature treatment

Sugak

Syvorotka²,

Buryy

et al. 2017

IOP Conf. Ser.: Mater. Sci. Eng.

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The changes in optical properties of bulk LiNbO 3 crystals were investigated depending on the diffusion depth. For this purpose the samples were isochronously annealed in hydrogen, subsequently the reduced samples were isochronously annealed in air. The investigations were held in different crystallographic directions. The experimentally determined distribution of depth-dependent additional absorption in reduced crystals was approximated basing on the oxygen vacancies diffusion model and solution of differential equations set describing the quasichemical reaction of bipolarons formation due to the oxygen loss in LiNbO 3 crystal. IntroductionHigh temperature annealing of lithium niobate (LiNbO 3 , LN) in vacuum, reducing and oxidizing environments, in the presence of metal ions, in proton-rich liquids etc is one of the techniques, which is extensively used to create LN-based elements for acoustoelectronics, optoelectronics and integrated optics [1][2][3]. However such thermochemical treatments alter the optical and electrical properties of LN. These changes are based on ions diffusion processes out of the crystal into the environment and vice versa, that affect the chemical composition of LN and its defect subsystem state. The diffusion processes in LiNbO 3 are studied in a significant amount of works, for example [4][5][6][7][8][9][10][11][12][13].Since in most cases diffusion surface layers with several microns thickness are sufficient for practical applications, the changes in chemical composition of LN layers in depth (and, consequently, changes in their properties) caused by the diffusion processes, are mainly studied by mass spectroscopy of secondary ions (SIMS) (see. e.g. [5]). This technique allows determining the changes only in micron-range and the measurements are performed in the direction of diffusion. Only in [6,7] the changes in the optical properties of bulk congruent LN samples with about 3 mm thickness, treated by VTE technique, were investigated by means of second harmonic generation conditions analysis and spectrometry in the direction, perpendicular to the direction of diffusion.Therefore the targeted investigations of coloration changes in LN crystals, caused by redox annealing, depending on the distance from crystals surface (for a few millimeters deep into the crystal) were not performed. Thereby it is not known how the coloration processes occur at different temperatures in crystals volume during redox treatment.Furthermore, the diffusion mechanisms during thermochemical treatments are also not completely clear. In [8] it is considered that the main diffusion mechanism in congruent LiNbO 3 , which contains no impurity ions, is the diffusion of lithium and lithium vacancies. In [9] it is assumed that both lithium and niobium diffusion processes take place simultaneously. Authors in [10,11] consider the oxygen diffusion as the main mechanism and in [4,12] -the diffusion of oxygen and lithium. Moreover, the known data about anisotropy of the diffusion processes is also controversial. For exa...

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Section: Annealing In Hmentioning

confidence: 95%

Spatial distribution of LiNbO₃single crystals optical properties changes after redox high-temperature treatment

Sugak

Syvorotka²,

Buryy

et al. 2017

IOP Conf. Ser.: Mater. Sci. Eng.

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“…Because the UV peak at 322 nm is near the UV absorption edge of CLN, it should be correlated with the O 2−/− -V Li − defect. Akhmadullin et al and Yan et al [20][21][22] reported that Q polarons can be formed in reduced CLN and serves as photorefractive centers. More importantly, Q polarons are responsible for the absorption band at about 3.5 eV.…”

Section: Absorption Spectramentioning

confidence: 99%

“…As electrons are the dominant carriers in our samples, intrinsic defects or clusters that can serve electrons to the conduction band may be considered photorefractive centers. As described in the Introduction, based on Li-vacancy model, the main intrinsic defects of CLN are Li vacancies (V Li − ) and [19]; and Q polarons can be considered a combination of two equivalent bipolarons [20][21][22].…”

Section: Absorption Spectramentioning

confidence: 99%

“…Crystals 2017, 9, 368 7 of 10 [20][21][22]. The UV absorption edge of CLN has also been attributed to the presence of Li vacancies-actually of O 2− ions, in the vicinity of VLi − [33].…”

Section: Absorption Spectramentioning

confidence: 99%

“…Meanwhile, Q polarons are responsible for the absorption band at approximately 3.5 eV in the UV region [20][21][22]. Q polarons may also be effectively excited by UV light and have the possibility to be UV photorefractive centers.…”

Section: Introductionmentioning

confidence: 99%

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Improvement in the Photorefractive Response Speed and Mechanism of Pure Congruent Lithium Niobate Crystals by Increasing the Polarization Current

et al. 2017

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A series of pure congruent lithium niobate (LiNbO 3 , 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.

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Infrared dispersion of dielectric function in Mg‐doped LiNbO₃ crystals with polaronic‐type conductivity

Китаева

Кузнецов

Shevlyuga

et al. 2007

J Raman Spectroscopy

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We have measured the refractive indices of Mg : LiNbO 3 crystals before and after chemical reduction at different annealing temperatures by the spontaneous parametric down-conversion technique and nearforward Raman scattering by polaritons in the range 2-11 µm. The polaron-induced contribution to the dispersion of the real part of the dielectric function was revealed near the phonon absorption edge. It was found that this contribution increases considerably with increase in the polaron concentration.

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Electronic structure of deep centers in LiNbO3

Cited by 32 publications

References 20 publications

Spatial distribution of LiNbO₃single crystals optical properties changes after redox high-temperature treatment

Spatial distribution of LiNbO₃single crystals optical properties changes after redox high-temperature treatment

Improvement in the Photorefractive Response Speed and Mechanism of Pure Congruent Lithium Niobate Crystals by Increasing the Polarization Current

Infrared dispersion of dielectric function in Mg‐doped LiNbO₃ crystals with polaronic‐type conductivity

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Electronic structure of deep centers in LiNbO3

Cited by 32 publications

References 20 publications

Spatial distribution of LiNbO3single crystals optical properties changes after redox high-temperature treatment

Spatial distribution of LiNbO3single crystals optical properties changes after redox high-temperature treatment

Improvement in the Photorefractive Response Speed and Mechanism of Pure Congruent Lithium Niobate Crystals by Increasing the Polarization Current

Infrared dispersion of dielectric function in Mg‐doped LiNbO3 crystals with polaronic‐type conductivity

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Product

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Spatial distribution of LiNbO₃single crystals optical properties changes after redox high-temperature treatment

Spatial distribution of LiNbO₃single crystals optical properties changes after redox high-temperature treatment

Infrared dispersion of dielectric function in Mg‐doped LiNbO₃ crystals with polaronic‐type conductivity