Pulse-induced transient blue absorption related with long-lived excitonic states in iron-doped lithium niobate

Messerschmidt, Simon; Bourdon, B.; Brinkmann, David; Krampf, Andreas; Vittadello, Laura; Imlau, Mirco

doi:10.1364/ome.9.002748

Cited by 8 publications

(14 citation statements)

References 30 publications

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“…Indeed, room-temperature transient absorption measurements on a series of Mg-doped and nominally pure LN samples by Conradi et al [26] also concluded that the primary signal at 785 nm stems from Nb 4+ free small polarons. Furthermore, subsequent work only found a secondary relatively weak and slow decay that most likely results from the recombination of self-trapped excitons pinned at various defects [29,31]. As shown in Figure 1, a single KWW function provides a satisfactory fit to our low-temperature data.…”

Section: Combining the Decay Of Lithium Niobate's Induced Absorption mentioning

confidence: 58%

“…The transient near infra-red absorption in LN is primarily due to small polarons [6,28]. Other optical phenomena are also associated with self-trapped charge carriers and excitons [29][30][31][32][33] We explore the transient absorption from 10 −7 to 10 5 s for temperatures between 45 K and 225 K. A simple model enables us to relate the observed decay rate of the absorption to the temperature-dependent small-polaron jump rate. Analysis of the small-polaron jump rate through the observed temperature range yields plausible estimates of the activation energy for small-polaron hopping and distinctively, the characteristic atomic-vibration frequency.…”

Section: Introductionmentioning

confidence: 99%

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Small-Polaron Hopping and Low-Temperature (45–225 K) Photo-Induced Transient Absorption in Magnesium-Doped Lithium Niobate

et al. 2020

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A strongly temperature-dependent photo-induced transient absorption is measured in 6.5 mol% magnesium-doped lithium niobate at temperatures ranging from 45 K to 225 K. This phenomenon is interpreted as resulting from the generation and subsequent recombination of oppositely charged small polarons. Initial two-photon absorptions generate separated oppositely charged small polarons. The existence of these small polarons is monitored by the presence of their characteristic absorption. The strongly temperature-dependent decay of this absorption occurs as series of thermally assisted hops of small polarons that facilitate their merger and ultimate recombination. Our measurements span the high-temperature regime, where small-polaron jump rates are Arrhenius and strongly dependent on temperature, and the intermediate-temperature regime, where small-polaron jump rates are non-Arrhenius and weakly dependent on temperature. Distinctively, this model provides a good representation of our data with reasonable values of its two parameters: Arrhenius small-polaron hopping’s activation energy and the material’s characteristic phonon frequency.

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Section: Combining the Decay Of Lithium Niobate's Induced Absorption mentioning

confidence: 58%

Section: Introductionmentioning

confidence: 99%

Small-Polaron Hopping and Low-Temperature (45–225 K) Photo-Induced Transient Absorption in Magnesium-Doped Lithium Niobate

et al. 2020

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“…In their revised excitation and relaxation model, different excitation paths entailing pinned-STE formation are proposed, which have recently been confirmed experimentally for Fe-doped crystals 30 . One of these paths is the band-to-band generation of electron-hole-pairs subsequently forming self-trapped excitons, which in turn migrate through the crystal until they are pinned on a defect.…”

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confidence: 79%

Superposed picosecond luminescence kinetics in lithium niobate revealed by means of broadband fs-fluorescence upconversion spectroscopy

Krampf

Messerschmidt

Imlau

2020

Sci Rep

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Various manifestations of small polarons strongly affect the linear and nonlinear optical properties of the oxide crystal lithium niobate (LiNbO 3 , Ln). While related transient absorption phenomena in Ln have been extensively studied in recent decades, a sound microscopic picture describing the blue-green (photo)luminescence of lithium niobate single crystals is still missing. in particular, almost nothing is known about: (i) the luminescence build-up and (ii) its room temperature decay. We present here the results of our systematic experimental study using nominally undoped and Mg-doped LN crystals with different Mg concentration. Picosecond luminescence was detected by means of femtosecond fluorescence upconversion spectroscopy (FLUPS) extended to the inspection of oxide crystals in reflection geometry. Two distinct luminescence decay components on the picosecond time scale are revealed. While a short exponential decay is present in each sample, a longer non-exponential decay clearly depends on the crystal composition. Since transient absorption spectroscopy excludes geminate small polaron annihilation as microscopic cause of the luminescence, both decay components are discussed in the context of self-trapped exciton (Ste) transport and decay. ABO 3 perovskite-like ferroelectrics exhibiting unique electronic properties 1 are important materials for optical frequency converters 2 , THz pulse generation 3 or promise advances in the fields of photovoltaics 4 , oxide electronics 5 and electroluminescent devices 6. In these materials, strong charge carrier-phonon coupling often lead to pronounced photo-induced polaronic effects manifesting in, e.g., laser-induced bulk damage 7,8 , and broad photoluminescence bands emitted from BO 6 octahedra 9-11. Lithium niobate is a frequently studied example of ferroelectric perovskite-like oxides, known for its rich defect structure leading to a conglomeration of intrinsic and extrinsic small polarons 7. Whereas light-induced phenomena in LN, such as transient absorption, have been extensively studied in recent decades relating them with formation and transport of small polarons 12-23 , a sound microscopic picture describing the blue-green (photo)luminescence of lithium niobate single crystals is still missing. While recently geminate small polaron annihilation has been proposed to lead to a two component luminescence decay in Mg-doped lithium niobate at low temperatures 24 , Messerschmidt et al. showed that low temperature luminescence and absorption decay on very different time scales 25. They revived the idea of radiatively decaying self-trapped excitons located at niobium-oxygen octahedra, which has been introduced over thirty years ago in the pioneering work of Blasse et al. 9,26-29. They concluded that an effect of STE formation on the light-matter interaction at elevated temperatures could per se no longer be neglected. In fact, no absorption feature of intrinsic self-trapped excitons has been reported so far, while Messerschmidt et al. related long-lived STEs pinned on ...

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“…In this work we critically summarize and partially reinterpret existing experimental results on UV-excited luminescence, time-resolved PL and TA in undoped and Mg or Fe-doped LiNbO 3 crystals taking into account also recent crucial data of Messerschmidt et al [28] on the selective excitation of long TA. We also present better resolved, fs-pulse-induced PL results, together with detailed temperature dependences of the reinterpreted parameters.…”

Section: Introductionmentioning

confidence: 90%

Excitonic hopping-pinning scenarios in lithium niobate based on atomistic models: different kinds of stretched exponential kinetics in the same system

Corradi

Krampf

Messerschmidt

et al. 2020

J. Phys.: Condens. Matter

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Based on a model of coupled processes with differently time-dependent decay kinetics we present a critical review on photoluminescence (PL) and transient absorption (TA) experiments in undoped and Mg or Fe-doped LiNbO 3 , together with a comprehensive interpretation of visible radiative and parallel non-radiative decay processes on timescales ranging from 50 ns up to minutes. Analogies and peculiarities of the kinetics of mobile self-trapped and pinned excitons are investigated and compared with those of hopping polarons in the same system. Exciton hopping with an activation energy of ≈0.18 eV is shown to govern the lifetime and quenching of the short PL component above 100 K. Strong interaction between excitons and dipolar pinning defects explains the exorbitant lifetimes and large depinning energies characterizing delayed TA components in doped LiNbO 3 , while restricted hopping of the pinned excitons is proposed to play a role in strongly delayed PL in LiNbO 3 :Mg exhibiting a narrowed emission band due to locally reduced electron-phonon coupling. Atomistic models of pinned excitons are proposed corresponding to charge-compensated dipolar defects predicted by theories of dopant incorporation in LiNbO 3 and are systematically assigned to absorption bands observed near the UV edge. Excitation in these bands is shown to lead directly to pinned exciton states confirming also the previously proposed two-step exciton-decay scenario in LiNbO 3 :Fe. Weak intrinsic sub-80 ns luminescence in congruent LiNbO 3 is explained as an opposite effect of enhanced electron-phonon coupling for excitons pinned on Nb Li antisite defects. The comparison of the different observed stretching behaviors in the paradigmatic system LiNbO 3 provides an intuitive picture of the underlying physical processes. The findings are relevant not only for holographic and non-linear optical applications of LiNbO 3 but are of general interest also for the treatment of stretched exponential or other time-dependent kinetics in complex condensed systems ranging from nanocrystals and polymers to liquids and biophysical systems.

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Pulse-induced transient blue absorption related with long-lived excitonic states in iron-doped lithium niobate

Cited by 8 publications

References 30 publications

Small-Polaron Hopping and Low-Temperature (45–225 K) Photo-Induced Transient Absorption in Magnesium-Doped Lithium Niobate

Small-Polaron Hopping and Low-Temperature (45–225 K) Photo-Induced Transient Absorption in Magnesium-Doped Lithium Niobate

Superposed picosecond luminescence kinetics in lithium niobate revealed by means of broadband fs-fluorescence upconversion spectroscopy

Excitonic hopping-pinning scenarios in lithium niobate based on atomistic models: different kinds of stretched exponential kinetics in the same system

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