Photoluminescence silicon nanocrystals

Figure 8 Schematic diagram of experimental setup and image of microplasma reactor with VHF source developed for the synthesis of photoluminescent silicon nanocrystals at room temperature (Nozaki et al, 2007a reproduced with permission). M.B. is a matching electrical circuit.

D. Riabinina, C. Durand, M. Chaker, and F. Rosei, Photoluminescent silicon nanocrystals synthesized by reactive laser ablation, Appl. Phys. Lett., 88, 073105-073108 [2006],... 

Germanenko et al. [153] suggested an explosive detector based on the photolumines-cence of silicon nanostructures. Silicon nanocrystals are first prepared by laser vaporization (LVCC). After suspension in methanol, the silicon nanocrstyals are excited by a laser at 355 nm, resulting in photoluminescence. They found that nitrotoluenes quench the photoluminescence from the silicon nanocrystals. Quenching rate constants for a number of nitro-compounds were presented. 

Warner JH, Tilley RD. Synthesis of water-soluble photolumines-cent germanium nanocrystals. Nanotechnol. 2006 17 3745-3749. Warner J, Hoshino A, Yamamoto K, Tilley R. Water-soluble photoluminescent silicon quantum dots. Angewandte Chemie-Internat. Ed. 2005 44 2-6. 

Silicon nanocrystals embedded into Si02 matrix demonstrate strong photoluminescence (PL) at room temperature in the range of 700-800 nm, whereas in sapphire such PL is not observed [1,2]. 

During the last few years, we have studied silicon nanocrystals produced by CO2 laser pyrolysis of silane and we have been able to show that, in these experiments, the PL characteristics can be unambiguously explained in terms of quantum confinement effects.However, to observe the photoluminescence with the naked eye, we had to wait a few hours or even a few days. It appeared that the silicon nanocrystals were passivated by natural aerial oxidation and that, with time, the photoluminescence became more and more intense. 

Figure 23.5. Mechanism of photoluminescence from nc-Si/Si02 nanocomposites Left pictorial illustration, right energy levels involved in (1) the photogeneration of electron-hole pairs in the silicon nanocrystals, the band gap and transition probabilities of which increase with decreasing crystallite size, which is followed by an energy transfer to localized radiative centers, such as (2) a non-bridging oxygen hole center (NBOHC) in the Si02 layer or (2 ) a metallic impurity.

The mechanism of the photoluminescence from nc-Si/Si02 nanocomposites includes a quantum confinement controlled photogeneration of electron-hole pairs within the silicon nanocrystals, followed by an energy transfer to nonbridging oxygen hole centers within the passivating Si02 matrix. The relatively inefficient and slow PL from such radiative centers is of little interest. A variety of other PL that have been reported in the literature and attributed to radiative recombination within the Si nanocrystals are most probably due to impurities. Several examples are shown to illustrate that extreme care has to be taken in order to avoid such artefacts. 

Takeda E, Nakamura T, Fujii M, Miura S, Hayashi S (2006) Surface plasmon polariton mediated photoluminescence from excitons in silicon nanocrystals. Appl Phys Lett 89(10) 101907 Tsybeskov L, Duttagupta SP, Fauchet PM (1995) Photoluminescence and electroluminescence in partially oxidized porous silicon. Solid State Commun 95(7) 429-433 Tsybeskov L, Duttagupta SP, Hirschman KD, Fauchet PM (1996) Stable and efficient electroluminescence from a porous silicon-based bipolar device. Appl Phys Lett 68(15) 2058-2060 Valenta J, Lalic N, Linnros J (2004) Electroluminescence of single silicon nanocrystals. Appl Phys Lett 84(9) 1459-1461... 

Optical gain 1-2, 4 in porous silicon 4 in silicone nanocrystals 2 Photoluminescence of porous silicon 3 Shifted-excitation-spot (SES) measurement 3 Stimulated emission 1-2 in silicon nanocrystals 2 Variable stripe length (VSL) technique 3... 

The photoluminescence of mesoporous silicon and silicon nanocrystals has received enormous study over the last 25 years. The spectroscopic nature and efficiency of various emission bands from the near-infrared to the ultraviolet are briefly reviewed, as are mechanistic studies on individual nanocrystals. Improvements in surface passivation and size control of sihcon nanocrystals have led to impressive photoluminescence quantum efficiencies in the visible range. 

The demonstration in 1990 that porous silicon could emit efficient tunable visible photoluminescence (PL) at room temperature and attributed to quantum-size effects in crystalline silicon (Canham 1990) has induced considerable worldwide research activities in order to (i) identify the various PL bands and their respective properties and emission mechanisms, (ii) optimize the PL efficiency, (iii) optimize the PL stability, and (iv) tailor the PL spectrum (peak wavelength and FWHM). This chapter reviews briefly the specificities of porous silicon PL measurements, the PL of individual silicon nanocrystals from porous silicon, and the PL of porous silicon layers. 

Ledoux G, Guillois O, Porterat D, Reynaud C, Huisken F, Kohn B, Paillard V (2000) Photoluminescence properties of silicon nanocrystals as a function of their size. Phys Rev B 62(23) 15942-15951... 

Hannah DC, Yang J, Podsiadlo P, Chan MKY, Demortiere A, Gosztola DJ, Prakapenka VB, Schatz GC, Kortshagen U, Schaller RD (2012) On the origin of photoluminescence in silicon nanocrystals pressure-dependent structural and optical studies. Nano Lett 12 4200 205 Harun NA, Horrocks BR, Fulton DA (2011) A miniemulsion polymerization technique for encapsulation of silicon quantum dots in polymer nanoparticles. Nanoscale 3 4733-4741 Heinrich JL, Curtis CL, Credo GM, Kavanagh KL, Sailor MJ (1992) Luminescent colloidal silicon suspensions from porous silicon. Science 255 66-68 Heitmaim J, Mueller F, Zacharias M, Goesele U (2005) Silicon nanocrystals size matters. Adv Mater 17 795-803... 

Henderson EJ, Shuhendler AJ, Prasad P, Baumann V, Maier-Flaig F, Faulkner DO, Lemmer U, Wu XY, Ozin GA (2011) Colloidally stable silicon nanocrystals with near-infrared photoluminescence for biological fluorescence imaging. Small 7 2507-2516... 

Gongalsky MB, Konstantinova EA, Osminkina LA, Timoshenko VY (2010) Deteetion of singlet oxygen in photoexcited porous silicon nanocrystals by photoluminescence measurements. Semiconductors 44 89-92... 

Photoluminescence of Silicon Nanocrystals. Si nanocrystals have also been synthesized. In this case laser vaporization of a Si target takes place in a pure He... 

Silicon nanocrystals coated with amphiphilic polymers Stable and bright photoluminescence in the pH range of 7-10 for biological tissue imaging Hessel et al. (2010)... 

Interestingly, it has been argued that nanoparticulate formation might be considered as a possibility for obtaining new silicon films [379]. The nanoparticles can be crystalline, and this fact prompted a new line of research [380-383], If the particles that are suspended in the plasma are irradiated with, e.g., an Ar laser (488 nm), photoluminescence is observed when they are crystalline [384]. The broad spectrum shifts to the red, due to quantum confinement. Quantum confinement enhances the bandgap of material when the size of the material becomes smaller than the radius of the Bohr exciton [385, 386]. The broad PL spectrum shows that a size distribution of nanocrystals exists, with sizes lower than 10 nm. 

P. M. Fauchet, Porous Silicon Photoluminescence and Electroluminescent Devices C. Delerue, G. Allan, and M. Lannoo, Theory of Radiative and Nonradiative Processes in Silicon Nanocrystallites L. Bros, Silicon Polymers and Nanocrystals... 

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