Temperature-induced crossover between bright and dark exciton emission in silicon nanoparticles

Lüttjohann, Stephan; Meier, Cedrik; Offer, Matthias; Lorke, Axel; Wiggers, Hartmut

doi:10.1209/0295-5075/79/37002

Cited by 15 publications

(32 citation statements)

References 32 publications

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“…9.5. When the temperature is lowered even further, the photoluminescence intensity decreases again without being fully quenched when approaching T → 0 K [20]. A similar behavior was reported for silicon nanocrystals in a SiO 2 layer by Brongersma et al [21].…”

Section: Recombination Dynamicssupporting

confidence: 77%

“…From this model, we obtain, as shown in Fig. 9.10, that for temperatures below T = 35 K, the recombination rate from the dark state is higher than that from the bright state [20]. This elucidates the competition between the contributions from these two states to the total recombination and this is also the reason why the intensity exhibits such a non-monotic behavior.…”

Section: R R (T ) ∝ I (T ) · R Plmentioning

confidence: 71%

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Optical Properties of Silicon Nanoparticles

Meier

Lorke

2012

Nanoparticles From the Gasphase

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This chapter reviews recent results on optical spectroscopy on silicon nanoparticles. The quantum confinement effect causing a spectral shift of the photoluminescence together with an intensity enhancement is discussed. The small spatial dimensions lead not only to a change of the electronic states, but affect also the vibronic spectrum as is seen in results on first-and second-order Raman scattering. Using time-resolved spectroscopy, the excitonic fine structure of silicon nanoparticles is investigated and a crossover of bright and dark exciton states is found. The analysis of the recombination dynamics allows to determine the size-dependence of the oscillator strength, which is in the order of 10 −5 and increases with decreasing particle size. Finally, we demonstrate an electroluminescence device based on silicon particles using impact ionization. IntroductionDue to the fact that most physical, chemical, and mechanical properties of nanostructured materials are determined by their structure, especially by geometry and size, many applications have been developed based on fundamental research in this field. The reasons for the novel effects in such nanomaterials are manifold, ranging from surface effects, e.g., in nanoparticle based gas sensors, to quantum confinement effects in sufficiently small structures. Among the inorganic materials used

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Section: Recombination Dynamicssupporting

confidence: 77%

Section: R R (T ) ∝ I (T ) · R Plmentioning

confidence: 71%

Optical Properties of Silicon Nanoparticles

Meier

Lorke

2012

Nanoparticles From the Gasphase

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“…As a result, the spontaneous emission of the BB level (maybe including the N B level) begins to decrease although the photogenerated carrier population continues to increase with increase of excitation density [also see Figs. [9][10][11].…”

Section: Stimulated Emission At High Excitation Densitiesmentioning

confidence: 99%

“…Although the dark state itself has been reported to radiatively relax at low temperatures (e.g., by releasing phonons), slow radiative recombination does take place since the dark exciton can undergo a thermal activation (or spin-flip) process thereby transferring into the bright state. 11,12 Furthermore, few reports address the relaxation dynamics (especially for the fast recombination process) if the excitation is increased by several orders of magnitude as compared to that in the regular spontaneous emission measurement, e.g., for investigating lasing from this kind of material. 13 Note that fast recombination at high densities (such as Auger process) has been mainly addressed for PbSe QDs.…”

Section: Introductionmentioning

confidence: 99%

Spontaneous and stimulated emission dynamics of PbS quantum dots in a glass matrix

2013

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Optical properties and relaxation mechanisms of PbS quantum dots in glass matrix (PbS:Glass) have been systematically investigated by transmission and (steady-state and transient) photoluminescence spectroscopy. Key parameters are determined by combining the data with semiempirical expressions, based on which the recombination mechanisms including spontaneous and stimulated emissions have been discussed as a function of temperature by referring to a multilevel model including intrinsic (or band-to-band transition), bright, dark, and ground states. The results disclose that (i) the existence of a dark exciton state is the main reason for thermal quenching of the emission even at low temperatures due to the strong multiacoustic phonon coupling, (ii) the "intrinsic" spontaneous emission related to the intrinsic state is observed with an approximately nanosecond lifetime, in contrast to the "regular" spontaneous emission from the bright exciton state with an approximately microsecond lifetime, and (iii) stimulated emission, which has a lifetime of 20-40 ps and shows power-dependence of excitation density (or temperature), only appears from the intrinsic state but not the (bright) exciton state when enough accumulation of photogenerated carriers is reached. Furthermore, we find that the thermal conductivity will become crucial for future PbS:Glass related optoelectronic device applications.

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“…͑4͒ and we cannot determine ⌫ B,rad and ⌫ D,rad on an absolute scale but only the ratio, R = ⌫ D,rad / ⌫ B,rad , as was also pointed out previously. [4][5][6] However, the ratio, A f / A s = ͓͑1 / 2͒͑1−R͒͑1−e −⌬/kT ͔͒ / ͑R + e −⌬/kT ͒, is independent on the specific experimental setup. Information about the total decay rates, ⌫ B and ⌫ D , and the spin-flip rates, ⌫ BD and ⌫ DB , can be extracted from ␥ s and ␥ f , respectively.…”

mentioning

confidence: 99%

Thermalization of exciton states in silicon nanocrystals

Julsgaard

Balling

et al. 2009

Applied Physics Letters

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Self-trapped excitons in silicon nanocrystals with sizes below 1.5 nm in Si/SiO 2 multilayers Silicon nanocrystals are studied by time-resolved fluorescence spectroscopy. After laser excitation the bright and dark exciton ground state levels are populated at random, but subsequently the decay curves reveal a thermalization between these levels. The characteristic thermalization time is found to be approximately 100 ns for temperatures below 100 K and surprisingly increases for higher temperatures. The decay curves are analyzed using a simple two-state model for the bright and dark exciton ground states.

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Temperature-induced crossover between bright and dark exciton emission in silicon nanoparticles

Cited by 15 publications

References 32 publications

Optical Properties of Silicon Nanoparticles

Optical Properties of Silicon Nanoparticles

Spontaneous and stimulated emission dynamics of PbS quantum dots in a glass matrix

Thermalization of exciton states in silicon nanocrystals

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