Near-Unity Internal Quantum Efficiency of Luminescent Silicon Nanocrystals with Ligand Passivation

Sangghaleh, Fatemeh; Sychugov, Ilya; Yang, Zhenyu; Veinot, Jonathan G. C.; Linnros, Jan

doi:10.1021/acsnano.5b01717

Cited by 123 publications

(154 citation statements)

References 47 publications

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“…We obtain the single-particle eigenstates {ε i ; ψ i (r)} of the Si NCs from direct diagonalization, in a basis set of plane-wave functions, of the Schrödinger equation [24]:…”

Section: B Atomistic Theorymentioning

confidence: 99%

“…Since Coulomb interactions bound an electron and a hole to form an exciton, excitonic states are admixture of electron and hole. Giving the dipole matrix and energy levels of exciton states, we are ready to obtain the absorption spectrum in many-body level [24]. For the modelling of matrix a fictitious, lattice-matched barrier material having a wide band gap and large type-I band offsets with respect to bulk Si was introduced.…”

Section: B Atomistic Theorymentioning

confidence: 99%

“…[24]. Since the modeling of the matrix is a fictitious, lattice-matched barrier, there is no need to relax the atomic positions.…”

Section: B Atomistic Theorymentioning

confidence: 99%

“…A 1 nm edge-to-edge distance is large enough to avoid the effects of supercell size even for as small as 2 nm diameter Si NC [24].…”

Section: B Atomistic Theorymentioning

confidence: 99%

“…The PL peak position is close to the calculated band gap (green peak at 1.88 eV). A typical featureless ensemble absorption [24] is also given for comparison (dashed line).…”

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confidence: 99%

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Single-dot absorption spectroscopy and theory of silicon nanocrystals

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“…We obtain the single-particle eigenstates {ε i ; ψ i (r)} of the Si NCs from direct diagonalization, in a basis set of plane-wave functions, of the Schrödinger equation [24]:…”

Section: B Atomistic Theorymentioning

confidence: 99%

Section: B Atomistic Theorymentioning

confidence: 99%

“…[24]. Since the modeling of the matrix is a fictitious, lattice-matched barrier, there is no need to relax the atomic positions.…”

Section: B Atomistic Theorymentioning

confidence: 99%

“…A 1 nm edge-to-edge distance is large enough to avoid the effects of supercell size even for as small as 2 nm diameter Si NC [24].…”

Section: B Atomistic Theorymentioning

confidence: 99%

“…The PL peak position is close to the calculated band gap (green peak at 1.88 eV). A typical featureless ensemble absorption [24] is also given for comparison (dashed line).…”

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confidence: 99%

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Single-dot absorption spectroscopy and theory of silicon nanocrystals

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Luminescent Transparent Wood

Veinot

et al. 2016

Advanced Optical Materials

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(1 of 5) 1600834 transition, where different nanocrystal materials were tested. Under blue/UV excitation the resulting 2 × 2 × 0.2 cm slabs exhibited diffused red and green luminescence arising from the embedded Si and CdSe QDs, respectively. Structures containing Si QDs offer a unique opportunity to evaluate scattering losses because the optically active Si QDs have negligible reabsorption at the emission wavelength. [15] The scattering strength of the luminescence was found to be dependent on the wood fiber direction, consistent with the original wood structure being preserved. High scattering values (i.e., up to ≈ 10 dB cm −1 ) indicate strong suppression of the total internal reflection required for emitted light propagation. This luminescent transparent wood nanocomposite offers interesting possibilities for applications, which can benefit from its unique structural and optical properties. Examples would be furniture for general lighting or luminescent solar concentrators for building integration, [16][17][18][19] where the proven mechanical strength of this transparent wood [11] is a clear advantage. The nontoxicity and material abundance of Si QDs further enables sustainable and large scale manufacturing of this new luminescent material.Silicon QDs were synthesized upon processing of hydrogen silsesquioxane by thermal annealing. [20] The resulting nanocrystal-containing silicon oxide composites were treated with ethanolic hydrofluoric acid to extract hydride terminated nanocrystals. It was followed by surface passivation using wellestablished hydrosilylation procedures described elsewhere. [21,22] Toluene dispersions of the resulting alkyl-passivated Si QDs feature external photoluminescence quantum yields in the range 30%-60%. [23] Samples used here had peak positions in the red (720 nm) and near infrared (870 nm) spectral range. To demons trate the possibility of incorporating different types of QDs commercially available CdSe/ZnS core/shell quantum dots with green emission (540 nm, Evident Technologies) were used.The wood template was obtained by delignification of wood veneer (balsa, Ochroma pyramidale, purchased from Wentzels Co. Ltd, Sweden) with dimension of 2 × 2 × 0.2 cm to remove the main light-absorbing component. [24] The thickness direction of the veneer is the tangential direction of the cross-section of the tree stem. Specifically, wood veneer was treated using 1 wt% of sodium chlorite (NaClO 2 , Sigma-Aldrich) in acetate buffer solution (pH 4.6) at 80 °C. The reaction was stopped when the wood appeared almost uniformly white. The delignified samples were washed with deionized water and kept in water until further use. Prior to polymer infiltration, wood samples were dehydrated upon sequential exposure to ethanol and acetone with each solvent exchange step repeated three times. The MMA monomer was pre-polymerized before mixing with QDs. The prepolymerization was completed by heating the MMA at 75 °C for 15 min with 0.3 wt% 2,2′-azobis (2-methylpropionitrile) followed by cooling to room temp...

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Erbium‐Hyperdoped Silicon Quantum Dots: A Platform of Ratiometric Near‐Infrared Fluorescence

Wang

2022

Advanced Optical Materials

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Hence, ratiometric near-IR (NIR) fluorescence has been recently proposed to realize the full potential of ratiometric fluorescence for sensing. [8,9] Among all kinds of materials that have ratiometric NIR fluorescence, quantum dots (QDs) hold great promise because of their facilely tunable emission and excellent stability against photobleaching. [10,11] Over the past decade, various types of QDs such as CdTe QDs, [12,13] carbon dots (CDs), [14] and silicon carbide QDs (SiC QDs) [15] have been explored to realize ratiometric NIR fluorescence. However, there exists spectral overlap between the absorption and emission of quantum dots that often contain Cd or Pb because of their direct bandgap. [4,16] The spectral overlap seriously reduces the signal-to-noise ratio (S/N) of ratiometric NIR fluorescence through reabsorption. [17] In addition, the separation between the dual NIR emission of Cd-or Pb-based QDs is usually small, [4] giving rise to mutual interference during the signal collection of ratiometric NIR fluorescence. [18] Therefore, the development of ratiometric NIR fluorescence without reabsorption and signal interference by designing and fabricating novel QDs are highly desired.It is well known that silicon QDs (Si QDs) are composed of non-toxic and earth-abundant Si, [19][20][21] which may efficiently emit NIR light at the wavelengths shorter than ≈1100 nm. [22,23] Given their quantum confinement and indirect bandgap, Si QDs only efficiently absorb UV light. [24][25][26] Hence, absorptionemission overlap and the resulting reabsorption do not occur to Si QDs. [27] Up to now, Si QDs have been extensively studied for bioimaging [28] and ions sensing. [29] Owing to the biocompatible and biodegradable properties of Si QDs they have potential to take the place of Cd-or Pb-based QDs, especially in biomedical fields. [28] In the meantime, erbium (Er) is known to be traditionally used to enable Si QDs to emit NIR light at the wavelength of ≈1540 nm ( 4 I 13/2 → 4 I 15/2 ), which is of importance for telecom systems. [30,31] Moreover, Er has the electronic configuration [Xe]4f 12 6s 2 . When incorporated in the host material, this configuration is changed to [Xe]4f 11 that is shielded from external fields by 5s 2 and 5p 6 electrons. [32] Therefore, the intra-4f luminescence are largely insensitive to the environment. [33] If Er 3+ is coupled with Si QDs, dual NIR emission without mutual interference can be obtained. Owing to the negligible reabsorption and emission signal interference, the Er-Si QDs coupled system may be a powerful platform of ratiometric NIR Ratiometric near-infrared (NIR) fluorescence holds great promise for important applications such as temperature sensing, food safety detection, and biological imaging owing to its self-calibration and contactless measurements in the NIR region. For ratiometric NIR fluorescence, the suppression of optical reabsorption and signal interference is crucial. In this work, freestanding erbium (Er)-hyperdoped silicon quantum dots (Si QDs) with UV absorption and NIR emi...

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Near-Unity Internal Quantum Efficiency of Luminescent Silicon Nanocrystals with Ligand Passivation

Cited by 123 publications

References 47 publications

Single-dot absorption spectroscopy and theory of silicon nanocrystals

Single-dot absorption spectroscopy and theory of silicon nanocrystals

Luminescent Transparent Wood

Erbium‐Hyperdoped Silicon Quantum Dots: A Platform of Ratiometric Near‐Infrared Fluorescence

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