Experimental study of NIR absorption due to Nb<sup>4+</sup>polarons in pure and Cr- or Ce-doped SBN crystals

Gao, Ming; Kapphan, S.; Porcher, S; Pankrath, R.

doi:10.1088/0953-8984/11/25/310

Cited by 18 publications

(14 citation statements)

References 40 publications

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“…The concentration dependent absorption in the UV-visible range in BCT:Fe, SBN:Ce and SBN:Cr reveals characteristic features reported earlier [15,16]. In SBN:Ce the FIR bands of Ce3+ near 2000 em -I give additional direct evidence of these centers [7].…”

Section: Optical Absorptionsupporting

confidence: 68%

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Light-Induced Polaronic Absorption at Low Temperature in Pure and (Fe, Ce, Cr) Doped Sr_xBa_1-xNb₂O₆or Ba_1-yCa_yTiO₃Crystals and Photodissociation of Vis Centers Into Small Polarons

Kapphan

Kislova

Wierschem

et al. 2003

Radiation Effects and Defects in Solids

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Congruent SBN and BCT crystals doped with Fe, Cr, Ce to enhance photorerractive properties. are investigated at low temperature (T> I K) under illumination with Art-and Kr+ -laser light. Light-induced absorption changes in a wide spectral range from UV to IR indicate photoinduced charge transfer processes from impurities to polaronic centers. Broad NIR absorptions (at about 0,7 eV) associated with Ti 1 + polarons in BCT or with Nb 4 + polarons in SBN are observed and their non-linear behaviour with illumination intensity, polarization and temperature is described on the basis of the simple model for the photo charge transport (in SBN: Ce-'+ + NbH-Ce 4 + + Nb4+). A broad visible absorption VIS (at about 2 eV) appearing together with the NIR polarons, is shown by photodissociation (with a Kr+ -laser) to consist at least partly of small polarons (in BCT and SBN). INTRODUCTIONBoth promising photorefractive crystal systems Ba 1 _rCa rTi03 and Sr:,Ba J-xNb206 possess a congruently melting mixture (for SBN x=0,61 and for BCTy=0.23), where melt and crystal have the same composition [I, 2]. This allows to grow large, homogeneous crystals of excellent optical quality, which is the basis for a wide range of optical applications [3]. Further favourable features of these crystals are the lack of a destructive phase transition (in contrast for instance to BaTi0 3 ) and the ease of poling of the crystals into a monodomain state [I]. Due to the statistical distribution of the constituents and a partially unfilled (tungsten bronze) structure for SBN, the ferroelectric phase transition (Tc ~ 373 K for congruent BCT pure and Tc ~ 353 K for congruent SBN pure) shows a relaxor type character with polar contributions well above Tc· The addition of doping ions (like Fe, Ce, Cr) in most cases shifts Tc toward lower temperatures with increasing doping content (for instance from 353 K in SBN pure to about room temperature for dopings of 20 000 ppm, p. f.u., Ce or Cr [ 4]. The electro-optical coefficients of the pure crystals are already large and can be enhanced considerably by suitable doping with polyvalent ions like those mentioned above [5, 6]. For some of the dopants (like Ce and Cr in SBN) a majority charge state 3 + has been determined [7, 8], however with an individual site occupancy, Ce3+ replacing Sr+ ions and C~+ sitting on the Nb 5 + sites [9, 10]. These dopants can be identified by their broad impurity induced absorption bands in the visible range, a shift of the UV-absorption edge to longer wavelength in the case of Cr doping and additional Far-IR bands (near 2000 em -I) in the case ofCe-doping [7]. A light-induced charge transport from these doping ions and trapping in shallow polaronic states (Ti3+ in BCT respectively Nb 4 + in SBN) has been identified by photo-EPR [11] and optical experiments [12] to constitute the underlying processes for the enhanced photorefractive properties in doped crystals. The majority of photo-excited charge carriers has been determined by laser beam coupling experiments [13] and Hall -effect [14...

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Section: Optical Absorptionsupporting

confidence: 68%

“…I b) [15,16]. The first absorption band (VIS centers) is observed around 2 eV and the second in the NIR around 0.7eV (6000cm-1 ).…”

Section: Light-induced Absorption Changes and Discussionmentioning

confidence: 97%

Light-Induced Polaronic Absorption at Low Temperature in Pure and (Fe, Ce, Cr) Doped Sr_xBa_1-xNb₂O₆or Ba_1-yCa_yTiO₃Crystals and Photodissociation of Vis Centers Into Small Polarons

Kapphan

Kislova

Wierschem

et al. 2003

Radiation Effects and Defects in Solids

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“…The Ce 3+ content can be identified by broad absorption band extending from the visible range to the UV band edge and additional far-infrared bands near 2000 cm - . Illumination with blue Ar + -laser or XBO lamp (with set of filters, 380-480 nm bandpass) light at low temperature creates light-induced absorption bands in the near infrared (NIR) and the visible range (VIS) [8]. The light-induced charge transport from the doping ions and trapping in shallow polaronic states has been identified to constitute the underlying process and first step leading to the build-up of a space charge field (under spatially inhomogeneous illumination).…”

Section: Introductionmentioning

confidence: 99%

Kinetics of light‐induced polaron‐ and VIS‐centers in SBN:Ce single crystals at low temperature

Gubaev

Kapphan

Kislova

et al. 2005

phys. stat. sol. (c)

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The promising photorefractive crystal Sr x Ba 1-x Nb 2 O 6 (SBN, congruent composition x=0.61) can be doped with polyvalent ions like Ce to enhance photorefractive properties. Illumination with blue Ar + -laser light at low temperature creates light-induced NIR and VIS absorption bands. The NIR absorption has been identified as being due to Nb 4+ electron polarons and their properties have been investigated in some detail. The VIS-Centers are less well understood and their nature is still under discussion. It has been shown by our previous measurements that illumination with red Kr + -laser light (647 nm) or red laser diodes (673 nm) leads to a dissociation of the VIS-Centers and a simultaneous build-up of a transient NIR-polaron absorption. We report here some new facts important for the simplified charge transfer model needed to describe quantitatively the equilibrium values and the dynamics of the NIR-polaron and VIS-center absorption. These features give new insight into the dynamic nature of these VIS-centers, which are currently being discussed as either bipolarons (in analogy to LiNbO 3 ) or polarons trapped at charged centers, or charge transfer vibronic exitons (CTVEs) being trapped at charged centers.

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“…In accordance with Refs. [6,12,13], the Nb 4+ polarons absorption in TBS and related crystals is observed around 60007000 cm −1 and is stable only at low temperatures. In such a way it should not be observed in our experiment.…”

Section: Resultsmentioning

confidence: 93%

“…One of the approaches of such study is investigation of the absorption changes induced by ionizing irradiation. Up to now, the induced absorption changes were studied only in SBN:Ce and SBN:Cr under visible light irradiation [5,6].…”

Section: Introductionmentioning

confidence: 99%

Stable Color Centers Induced in Pure and Neodymium Doped Ca_0.28Ba_0.72Nb₂O₆Crystals by Gamma Irradiation

2015

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The work is devoted to investigation of stable coloration induced by gamma radiation from 60 Co (1.25 MeV) in pure and neodymium doped Ca0.28Ba0.72Nb2O6 single crystals. Nature of the induced absorption is discussed. This absorption is due to charge change of native defects or ions forming of crystals (vacancy, niobium ions, etc.). The nature of color centers responsible for induced absorption is discussed.

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Experimental study of NIR absorption due to Nb⁴⁺polarons in pure and Cr- or Ce-doped SBN crystals

Cited by 18 publications

References 40 publications

Light-Induced Polaronic Absorption at Low Temperature in Pure and (Fe, Ce, Cr) Doped Sr_xBa_1-xNb₂O₆or Ba_1-yCa_yTiO₃Crystals and Photodissociation of Vis Centers Into Small Polarons

Light-Induced Polaronic Absorption at Low Temperature in Pure and (Fe, Ce, Cr) Doped Sr_xBa_1-xNb₂O₆or Ba_1-yCa_yTiO₃Crystals and Photodissociation of Vis Centers Into Small Polarons

Kinetics of light‐induced polaron‐ and VIS‐centers in SBN:Ce single crystals at low temperature

Stable Color Centers Induced in Pure and Neodymium Doped Ca_0.28Ba_0.72Nb₂O₆Crystals by Gamma Irradiation

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Experimental study of NIR absorption due to Nb4+polarons in pure and Cr- or Ce-doped SBN crystals

Cited by 18 publications

References 40 publications

Light-Induced Polaronic Absorption at Low Temperature in Pure and (Fe, Ce, Cr) Doped SrxBa1-xNb2O6or Ba1-yCayTiO3Crystals and Photodissociation of Vis Centers Into Small Polarons

Light-Induced Polaronic Absorption at Low Temperature in Pure and (Fe, Ce, Cr) Doped SrxBa1-xNb2O6or Ba1-yCayTiO3Crystals and Photodissociation of Vis Centers Into Small Polarons

Kinetics of light‐induced polaron‐ and VIS‐centers in SBN:Ce single crystals at low temperature

Stable Color Centers Induced in Pure and Neodymium Doped Ca0.28Ba0.72Nb2O6Crystals by Gamma Irradiation

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Product

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Experimental study of NIR absorption due to Nb⁴⁺polarons in pure and Cr- or Ce-doped SBN crystals

Light-Induced Polaronic Absorption at Low Temperature in Pure and (Fe, Ce, Cr) Doped Sr_xBa_1-xNb₂O₆or Ba_1-yCa_yTiO₃Crystals and Photodissociation of Vis Centers Into Small Polarons

Light-Induced Polaronic Absorption at Low Temperature in Pure and (Fe, Ce, Cr) Doped Sr_xBa_1-xNb₂O₆or Ba_1-yCa_yTiO₃Crystals and Photodissociation of Vis Centers Into Small Polarons

Stable Color Centers Induced in Pure and Neodymium Doped Ca_0.28Ba_0.72Nb₂O₆Crystals by Gamma Irradiation