scholarly journals Silicon Nanocrystals: Fundamental Theory and Implications for Stimulated Emission

2008 ◽  
Vol 2008 ◽  
pp. 1-32 ◽  
Author(s):  
V. A. Belyakov ◽  
V. A. Burdov ◽  
R. Lockwood ◽  
A. Meldrum
Keyword(s):  
Energy Transfer ◽  
Silicon Nanocrystals ◽  
Light Emission ◽  
Theoretical Calculations ◽  
Energy Levels ◽  
Optical Gain ◽  
Stimulated Emission ◽  
Recombination Rates ◽  
Physical Mechanisms ◽  
Gain Profile

Silicon nanocrystals (NCs) represent one of the most promising material systems for light emission applications in microphotonics. In recent years, several groups have reported on the observation of optical gain or stimulated emission in silicon NCs or in porous silicon (PSi). These results suggest that silicon-NC-based waveguide amplifiers or silicon lasers are achievable. However, in order to obtain clear and reproducible evidence of stimulated emission, it is necessary to understand the physical mechanisms at work in the light emission process. In this paper, we report on the detailed theoretical aspects of the energy levels and recombination rates in doped and undoped Si NCs, and we discuss the effects of energy transfer mechanisms. The theoretical calculations are extended toward computational simulations of ensembles of interacting nanocrystals. We will show that inhomogeneous broadening and energy transfer remain significant problems that must be overcome in order to improve the gain profile and to minimize nonradiative effects. Finally, we suggest means by which these objectives may be achieved.

Possible Mechanism of the 30–100 Picoseconds Fast and Efficient Photoluminescence From nc-Si/a-SiO2Doped with Transition Metals

1996 ◽  
Vol 452 ◽  
Author(s):  
S. Veprek ◽  
Th. Wirschem ◽  
J. Dian ◽  
S. Perná ◽  
R. Merica ◽  
...  
Keyword(s):  
Thin Films ◽  
Energy Transfer ◽  
Transition Metals ◽  
Comparative Study ◽  
Silicon Nanocrystals ◽  
Light Emission ◽  
Uv Light ◽  
Charge Carriers ◽  
Radiative Center ◽  
Insight Into

AbstractThe nc-Si/a-SiO2composite thin films doped with tungsten show very fast and efficient photoluminescence (PL). In order to obtain insight into the PL mechanism we have performed a comparative study with other metals. The results lend support to the suggested mechanism which includes the photogeneration of charge carriers due to efficient absorption of the excitation UV light in the silicon nanocrystals followed by energy transfer to the Wn+radiative center from which the light emission occurs.

Grains of Porous Silicon Embedded in SiO2:Studies of Optical Gain and Electroluminescence

2004 ◽  
Vol 99-100 ◽  
pp. 31-36 ◽  
Author(s):  
K. Dohnalová ◽  
K. Luterová ◽  
J. Valenta ◽  
Jiří Buršík ◽  
M. Procházka ◽  
...  
Keyword(s):  
Porous Silicon ◽  
Silicon Nanocrystals ◽  
Visible Region ◽  
Optical Gain ◽  
Intrinsic Property ◽  
Stimulated Emission ◽  
Silicon Nanostructures ◽  
Porous Si ◽  
Si Nanocrystals ◽  
Excitation Spot

Recent reports on experimental observation of optical gain in silicon nanostructures in the visible region, performed at several laboratories all over the world, have triggered an extraordinary surge of interest in silicon lasing. However, attempts aimed at reproducing the red stimulated emission from „standard“silicon nanocrystals (sized 3-5 nm) at some other laboratories either failed, or. did not come to definite conclusions. Therefore, more detailed measurements of optical gain in a wider variety of samples containing Si nanocrystals are required in order to unravel whether or not the observation of optical gain is an intrinsic property of Si nanocrystals. We have performed a detailed study of optical gain in layers of densely packed Si nanocrystals in SiO2, prepared on the basis of porous Si, using the variable-stripe-length (VSL) method in combination with the shifted-excitation-spot (SES) method. In selected samples we have observed a distinct difference in behaviour between VSL and SES curves, indicating the occurrence of positive optical gain of ~ 24 cm-1. Preliminary reports on transport and electroluminescence measurements in thin films of SiO2 doped with porous silicon grains, prepared by spin-coating technique, are also discussed.

Optical Gain in Foerster Energy Transfer Based Organic Guest-Host-Systems

2009 ◽  
Vol 1197 ◽  
Author(s):  
Torsten Rabe ◽  
Sebastian Döring ◽  
Niko Hildebrandt ◽  
Thomas Riedl ◽  
Wolfgang Kowalsky ◽  
...  
Keyword(s):  
Energy Transfer ◽  
Cross Section ◽  
Emission Cross Section ◽  
Pump Energy ◽  
Optical Gain ◽  
Stimulated Emission ◽  
Wide Range ◽  
Förster Energy Transfer ◽  
Donor Acceptor ◽  
Stimulated Emission Cross Section

AbstractWe study the optical gain for various doping concentrations in a dye doped polymer (poly-[9,9-dioctylfluorene] with 6,6'-[2,2'-octyloxy-1,1'-binaphthyl] spacer groups (BN-PFO) doped by the stilbene dye 1,4-bis[2-[4-[N,N-di[p-tolyl]amino]phenyl]vinyl-benzene] (DPAVB)). In such a guest-host-system (GHS) the occupation of the upper laser level (dopant site) is due to Förster energy transfer (FET), which strongly depends on the donor acceptor distance and hence on the concentration of the laser dye. Therefore, the doping concentration is varied over a wide range and the gain coefficients are measured at various excitation densities to analyze the stimulated emission cross section.For the investigated GHS maximum gain coefficients up to ∼340 1/cm were found at absorbed pump energy densities of around 50 μJ/cm2. It will be shown that the stimulated emission cross section (σ = 1.8 × 10−16 cm2) is concentration independent which is quite different to a recently investigated small molecule based GHS. These effects will be discussed considering the rate and exciton diffusion constants.

Modification of Visible Light Emission from Silicon Nanocrystals as a Function of Size, Electronic Structure, and Surface Passivation

1998 ◽  
Vol 536 ◽  
Author(s):  
M.V. Wolkin ◽  
J. Jorne ◽  
P.M. Fauchet ◽  
G. Allan ◽  
C. Delerue
Keyword(s):  
Porous Silicon ◽  
Silicon Nanocrystals ◽  
Surface Passivation ◽  
Light Emission ◽  
Electrochemical Etching ◽  
Theoretical Calculations ◽  
Surface Oxidation ◽  
Stain Etching ◽  
Visible Light Emission ◽  
Effect Of Surface

AbstractThe effect of surface passivation and crystallite size on the photoluminescence of porous silicon is reported. Oxygen-free porous silicon samples with medium to ultra high porosities have been prepared by using electrochemical etching followed by photoassisted stain etching. As long as the samples were hydrogen-passivated the PL could be tuned from the red (750nm) to the blue (400nm) by increasing the porosity. We show that when surface oxidation occurred, the photoluminescence was red-shifted. For sizes smaller than 2.8nm, the red shift can be as large as 1eV but for larger sizes no shift has been observed. Comparing the experimental results with theoretical calculations, we suggest that the decrease in PL energy upon exposure to oxygen is related to recombination involving an electron or an exciton trapped in Si=O double bonds. This result clarifies the recombination mechanisms in porous silicon.

scholarly journals Optical Properties and White Light Emission of Dy3+ Doped Alumino Borotellurite Glasses

2019 ◽  
Vol 35 (4) ◽  
Author(s):  
Phan Van Do
Keyword(s):  
Optical Properties ◽  
Light Emission ◽  
Transition Probability ◽  
Emission Cross Section ◽  
Optical Gain ◽  
Emission Feature ◽  
Stimulated Emission ◽  
Luminescence Spectra ◽  
Intensity Parameters ◽  
Chromaticity Coordinates

Dy3+ doped alumino borotellurite (ABT) glasses xB2O3+(80-x)TeO2+10Al2O3+10CaO+ 0.5Dy2O3 (where x = 35; 45 and 55) have been prepared by melting method. Their optical properties were studied through absorption, luminescence spectra and decay time measurements. Judd-Ofelt (JO) intensity parameters (Ωλ, λ = 2, 4 and 6) have been determined using absorption spectra and are been used to calculate the radiative parameters like transition probability, stimulated emission cross-section, branching ratios, gain band width and optical gain for the 4F9/2→6H13/2 transition in Dy3+ ions. The chromaticity coordinates is used to estimate the emission feature of prepared glasses.

Optical gain and stimulated emission in silicon nanocrystals

2002 ◽  
Vol 738 ◽  
Author(s):  
L. Dal Negro ◽  
M. Cazzanelli ◽  
Z. Gaburro ◽  
P. Bettotti ◽  
L. Pavesi ◽  
...  
Keyword(s):  
Silicon Nanocrystals ◽  
Chemical Vapour ◽  
Optical Gain ◽  
Pump Intensity ◽  
Stimulated Emission ◽  
Thin Layers ◽  
Threshold Behaviour ◽  
Time Resolved ◽  
Emission Signal ◽  
Length Measurements

ABSTRACTTime-resolved luminescence measurements on silicon nanocrystal waveguides have revealed a fast recombination dynamics, related to population inversion which leads to net optical gain. The waveguide samples were obtained by thermal annealing of plasma enhanced chemical vapour deposited thin layers of silicon rich oxide Variable stripe length measurements performed on the fast emission signal have shown an exponential growth of the amplified spontaneous emission, with net gain values of about 10 cm-1. Both the fast component intensity and its temporal width revealed threshold behaviour as a function of the incident pump intensity. A modelling of the decay dynamics is suggested within an effective four level rate equation treatment including the delicate interplay among stimulated emission and Auger recombinations.

Pump-Probe Measurements Using Silicon Nanocrystal Waveguides

2003 ◽  
Vol 770 ◽  
Author(s):  
Nathanael Smith ◽  
Max J. Lederer ◽  
Marek Samoc ◽  
Barry Luther-Davies ◽  
Robert G. Elliman
Keyword(s):  
Probe Beam ◽  
Time Resolution ◽  
Pump Beam ◽  
Silicon Nanocrystals ◽  
Continuous Wave ◽  
Optical Gain ◽  
Optical Pump ◽  
Time Resolved ◽  
Pump Probe ◽  
Probe Measurements

AbstractOptical pump-probe measurements were performed on planar slab waveguides containing silicon nanocrystals in an attempt to measure optical gain from photo-excited silicon nanocrystals. Two experiments were performed, one with a continuous-wave probe beam and a pulsed pump beam, giving a time resolution of approximately 25 ns, and the other with a pulsed pump and probe beam, giving a time resolution of approximately 10 ps. In both cases the intensity of the probe beam was found to be attenuated by the pump beam, with the attenuation increasing monotonically with increasing pump power. Time-resolved measurements using the first experimental arrangement showed that the probe signal recovered its initial intensity on a time scale of 45-70 μs, a value comparable to the exciton lifetime in Si nanocrystals. These data are shown to be consistent with an induced absorption process such as confined carrier absorption. No evidence for optical gain was observed.

Thymine Dimerization Induced by Oxidative DNA Lesions and Epigenetic Intermediates via Triplet-Triplet Energy Transfer

2020 ◽  
Author(s):  
Mauricio Lineros-Rosa ◽  
Antonio Francés-Monerris ◽  
Antonio Monari ◽  
Miguel Angél Miranda ◽  
Virginie Lhiaubet-Vallet
Keyword(s):  
Energy Transfer ◽  
Excitation Energy ◽  
Transient Absorption ◽  
Theoretical Calculations ◽  
Dna Lesions ◽  
Transient Absorption Spectroscopy ◽  
Triplet Energy ◽  
Pyrimidine Dimers ◽  
Triplet Energy Transfer ◽  
Dna Nucleobases

Interaction of nucleic acids with light is a scientific question of paramount relevance not only in the understanding of life functioning and evolution, but also in the insurgence of diseases such as malignant skin cancer and in the development of biomarkers and novel light-assisted therapeutic tools. This work shows that the UVA portion of sunlight, not absorbed by canonical DNA nucleobases, can be absorbed by 5-formyluracil (ForU) and 5-formylcytosine (ForC), two ubiquitous oxidative lesions and epigenetic intermediates present in living beings in natural conditions. We measure the strong propensity of these molecules to populate triplet excited states able to transfer the excitation energy to thymine-thymine dyads, inducing the formation of the highly toxic and mutagenic cyclobutane pyrimidine dimers (CPDs). By using steady-state and transient absorption spectroscopy, NMR, HPLC, and theoretical calculations, we quantify the differences in the triplet-triplet energy transfer mediated by ForU and ForC, revealing that the former is much more efficient in delivering the excitation energy and producing the CPD photoproduct. Although significantly slower than ForU, ForC is also able to harm DNA nucleobases and therefore this process has to be taken into account as a viable photosensitization mechanism. The present findings evidence a rich photochemistry crucial to understand DNA photodamage and of potential use in the development of biomarkers and non-conventional photodynamic therapy agents.

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