Breakdown of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>k</mml:mi></mml:math>-Conservation Rule in Si Nanocrystals

Kovalev, D.; Heckler, H.; Ben‐Chorin, M.; Polisski, G.; Schwartzkopff, M.; Koch, F.

doi:10.1103/physrevlett.81.2803

Cited by 290 publications

(180 citation statements)

References 18 publications

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“…[1][2][3][4][5] In photoluminescence, upon illumination, incoming photons are predominantly absorbed by band-to-band transitions in Si NCs. Since the indirect band structure of Si is preserved also in the nanocrystalline form, 6 electron-hole pairs generated in this way are characterized by a relatively long lifetime. This enables energy transfer to Er 3+ ions located in vicinity of Si NCs.…”

Section: Introductionmentioning

confidence: 99%

Energy transfer in Er-dopedSiO2sensitized with Si nanocrystals

et al. 2008

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We present a high-resolution photoluminescence study of Er-doped SiO 2 sensitized with Si nanocrystals ͑Si NCs͒. Emission bands originating from recombination of excitons confined in Si NCs, internal transitions within the 4f-electron core of Er 3+ ions, and a band centered at Ϸ 1200 nm have been identified. Their kinetics were investigated in detail. Based on these measurements, we present a comprehensive model for energy-transfer mechanisms responsible for light generation in this system. A unique picture of energy flow between the two subsystems was developed, yielding truly microscopic information on the sensitization effect and its limitations. In particular, we show that most of the Er 3+ ions available in the system are participating in the energy exchange. The long-standing problem of apparent loss of optical activity in the majority of Er dopants upon sensitization with Si NCs is clarified and assigned to the appearance of a very efficient energy exchange mechanism between Si NCs and Er 3+ ions. Application potential of SiO 2 : Er, sensitized by Si NCs, was discussed in view of the newly acquired microscopic insight.

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Section: Introductionmentioning

confidence: 99%

Energy transfer in Er-dopedSiO2sensitized with Si nanocrystals

et al. 2008

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“…4 The Si-nc mediated energy transfer offers an effective excitation cross section of~10 −16 cm 2 , 5,6 much higher than the 10 −21 −10 −19 cm 2 cross section of resonant excitation for Er 3+ in SiO 2 . 5,7 In this heterogeneous medium ͑SiO 2 : Si-nc, Er͒ the incoming photons are captured in Si-nc due to efficient bandto-band absorption, 8 and subsequently, the excitation energy is transferred to Er 3+ ions located preferably outside Si-nc. 9,10 In this way, an efficient channel for nonresonant excitation leading to temperature-stable Er 3+ emission is realized.…”

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confidence: 99%

Sensitization of Er luminescence by Si nanoclusters

et al. 2004

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“…17,18 A few electronic structure calculations on alkylated SiNCs have been made using density functional methods: these calculations include Si 29 clusters passivated with CH 3 or CH 2 ͑Ref. 19͒ and, more recently, alkyl monolayers up to C 4 H 9 on cluster sizes from Si 20 to Si 142 .…”

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confidence: 99%

Optical luminescence from alkyl-passivated Si nanocrystals under vacuum ultraviolet excitation: Origin and temperature dependence of the blue and orange emissions

Chao

Houlton

Horrocks

et al. 2006

Applied Physics Letters

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The origin and stability of luminescence are critical issues for Si nanocrystals which are intended for use as biological probes. The optical luminescence of alkyl-monolayer-passivated silicon nanocrystals was studied under excitation with vacuum ultraviolet photons ͑5.1-23 eV͒. Blue and orange emission bands were observed simultaneously, but the blue band only appeared at low temperatures ͑Ͻ175 K͒ and with high excitation energies ͑Ͼ8.7 eV͒. At 8 K, the peak wavelengths of the emission bands were 430± 2 nm ͑blue͒ and 600± 2 nm ͑orange͒. The orange and blue emissions originate from unoxidized and oxidized Si atoms, respectively. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2216911͔Silicon nanostructures have attracted great interest since the observation of their efficient visible photoluminescence at room temperature in the early 1990s. 1-4 Silicon nanocrystals ͑SiNCs͒ are potential building blocks of future electronic and photonic devices. They also have promise as luminescent labels in biological applications, 5-9 because they show red-orange luminescence at small particle sizes ͑ca. 2 nm diam͒ and are not expected to show some aspects of the toxicity of cadmium-based semiconductors. However, the stability of SiNCs towards O 2 and H 2 O is a concern. Recently, several groups, including ourselves, have prepared alkyl-passivated silicon nanocrystals. [5][6][7][8][9][10][11][12][13][14][15][16] These are SiNCs whose surface is capped by a monolayer of saturated hydrocarbon molecules and anchored to the Si core via covalent Si-C bonds. Although the particles contain a little oxide from their preparation, the alkyl monolayer protects the Si core and they are not oxidized further under ambient conditions. 6 The reaction used to prepare the capping monolayer is sufficiently general to allow manipulation of the chemical functionality on the particle surface, e.g., for synthesis of DNA strands. 6 However, it is also important to characterize the physical properties, especially the luminescence, of these systems because the utility of the particles depends on their luminescence upon insertion into biological cells.Compared to the generally weak IR luminescence of bulk silicon ͑observed at low temperatures͒, the efficiency of photoluminescence ͑PL͒ from Si nanostructures is strongly increased due to the greater overlap of the electron and hole wave functions and the decrease in efficiency of nonradiative pathways. 17,18 A few electronic structure calculations on alkylated SiNCs have been made using density functional methods: these calculations include Si 29 clusters passivated with CH 3 or CH 2 ͑Ref. 19͒ and, more recently, alkyl monolayers up to C 4 H 9 on cluster sizes from Si 20 to Si 142 . 20 Theoretical work suggests that the band gap of SiNCs is little changed upon alkylation of the hydrogen-terminated particle surface, but the positions of the band edges are shifted significantly towards the vacuum level and the properties of the excited states are affected. 20 Experimental studies of the PL mechanism o...

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Breakdown of thek-Conservation Rule in Si Nanocrystals

Cited by 290 publications

References 18 publications

Energy transfer in Er-dopedSiO2sensitized with Si nanocrystals

Energy transfer in Er-dopedSiO2sensitized with Si nanocrystals

Sensitization of Er luminescence by Si nanoclusters

Optical luminescence from alkyl-passivated Si nanocrystals under vacuum ultraviolet excitation: Origin and temperature dependence of the blue and orange emissions

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