Three-dimensional phonon confinement in CdSe microcrystallites in glass

Rodden, W S O; Torres, C. M. Sotomayor; Ironside, C. N.

doi:10.1088/0268-1242/10/6/011

Cited by 30 publications

(25 citation statements)

References 14 publications

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“…37 Consequently light scattering takes place from quasi-zonecentre optical phonons with wave vectors q up to /d. This is in fact valid only for weak phonon localization and not for completely confined phonons.…”

Section: The Gaussian Confinement Modelmentioning

confidence: 99%

“…In many investigations, quantitative fitting of the phonon line shape has also been carried out. 37,40,78 The results are grouped into four subsections.…”

Section: Isolated and Compacted Nanoparticles And Nanocompositesmentioning

confidence: 99%

“…The system CdS x Se 1 x exhibits a two-mode behaviour, and both CdSe-like and CdS-like confined LO phonons are observed. 37 On the other hand, the Cd 1 x Zn x S system exhibits the one-mode behaviour. The blue-shift of the LO phonon wavenumber during the late stage of annealing of Cd 1 x Zn x S nanoparticles dispersed in oxide glass host that contained 20% ZnO has been attributed to a change in the stoichiometry (x) from 0.16 to 0.23 in the nanoparticle.…”

Section: Semiconductor-doped Glasses and Mixed Crystalsmentioning

confidence: 99%

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Raman spectroscopy of optical phonon confinement in nanostructured materials

Arora

Rajalakshmi

Ravindran

et al. 2007

J Raman Spectroscopy

358

294

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If the medium surrounding a nano-grain does not support the vibrational wavenumbers of a material, the optical and acoustic phonons get confined within the grain of the nanostructured material. This leads to interesting changes in the vibrational spectrum of the nanostructured material as compared to that of the bulk. Absence of periodicity beyond the particle dimension relaxes the zone-centre optical phonon selection rule, causing the Raman spectrum to have contributions also from phonons away from the Brillouin-zone centre. Theoretical models and calculations suggest that the confinement results in asymmetric broadening and shift of the optical phonon Raman line, the magnitude of which depends on the widths of the corresponding phonon dispersion curves. This has been confirmed for zinc oxide nanoparticles. Microscopic lattice dynamical calculations of the phonon amplitude and Raman spectra using the bond-polarizability model suggest a power-law dependence of the peak-shift on the particle size. This article reviews recent results on the Raman spectroscopic investigations of optical phonon confinement in several nanocrystalline semiconductor and ceramic/dielectric materials, including those in selenium, cadmium sulphide, zinc oxide, thorium oxide, and nano-diamond. Resonance Raman scattering from confined optical phonons is also discussed.

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Section: The Gaussian Confinement Modelmentioning

confidence: 99%

“…In many investigations, quantitative fitting of the phonon line shape has also been carried out. 37,40,78 The results are grouped into four subsections.…”

Section: Isolated and Compacted Nanoparticles And Nanocompositesmentioning

confidence: 99%

Section: Semiconductor-doped Glasses and Mixed Crystalsmentioning

confidence: 99%

See 1 more Smart Citation

Raman spectroscopy of optical phonon confinement in nanostructured materials

Arora

Rajalakshmi

Ravindran

et al. 2007

J Raman Spectroscopy

358

294

View full text Add to dashboard Cite

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“…(5, a,b). A strong first order longitudinal optical (1LO) phonon mode of S3 and S1 centered at 209 cm 1 and 204 cm 1 with a small asymmetry in S1 are identified and are red shifted by 1 cm 1 and 6 cm 1 respectively from the standard CdSe bulk samples whose 1LO appears at 210 cm 1 [33]. One of the important factor, responsible for the observed 1LO phonon frequency decrease with size reduction, is the contribution non-zero wavevector phnons due to Raman selection rule relaxation caused by phonon confinement in a small nanocrystal volume.…”

Section: Intensity (Arb Units)mentioning

confidence: 96%

“…The phonon confinement not only results phonon frequency decrease but also in a line shape asymmetry more in the low frequency wing. The position of 1LO phonon mode can be calculated using the relation [34], w = w 0 -8.87/ R 2 where w 0 is the standard bulk phonon mode of CdSe= 210 cm 1 [33], R is the radius of the nanocrystal. Here, the photon (laser) beam diameter for Raman scattering measurement is 10 μm and the nanocrystal size regimes for S1 and S3 are 4 to 15 nm.…”

Section: Intensity (Arb Units)mentioning

confidence: 99%

Effect of Bimodal Size Distribution on Optical Properties of CdSe Nanocrystals

Sarangi

Hussain²,

Sahu

2011

CNANO

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Effect of bimodal size distribution (BSD) on optical properties of electrodeposited CdSe nanocrystalline thin films is reported. Grazing angle X-ray diffraction identifies two different nanocrystalline size regimes with both compressive and tensile strains coexisting in the same sample. The two size regimes change their size with the change of electrodeposition current density or temperature. Optical absorption studies reveal two absorption edges corresponding to the two different sizes. Presence of two well separated photoluminescence (PL) bands due to excitonic recombination supports the presence of BSD in the sample which is also confirmed from temperature dependent PL measurements. The origin of the two PL bands are attributed to the transfer of thermally activated carriers between two size regimes accompanied by excitonic recombination. Micro Raman scattering of nanocrystalline CdSe at 300K showed softening of Raman phonon modes due to small size nanocrystallites but do not reflect the BSD effect. INTRODUCTIONIn recent years, considerable research efforts have been made towards the fabrication, characterization and exploitation of semiconductor nanocrystals (NCs) for possible application in electroluminescent devices [1,2], biosensors [3,4] and imaging based on their optical properties [5]. However, the NC optical properties are often influenced by their size, shape, strain and their bimodal/ multimodal size distribution. Semiconductor NCs [6] with size less than or comparable to Bohr exciton [7] radius exhibit size quantization effect (SQE) where one can observe blue shifts in their optical absorption because of the discritization of electronic energy levels within the band gap. Some of the important optical properties associated with semiconductor NCs are as under:With increasing NC size, the absorption threshold shifts to longer wavelength [8]. Photoluminescence (PL) properties are size, size distribution and shape dependent. Large size NCs show band edge [9] PL i.e the carrier recombination is between the conduction band electrons and valence band hole where as for very small NCs, the PL exibit excitonic effect with a stokes shift. The PL involves a nonradiative transition of photoexcited electrons from the conduction band maxima to sub-bands followed by radiative transition from sub-band to valence band maxima. Hence, excitonic transitions in semiconductor NCs are generally observed at lower energies compared to the absorption edge. Due to large surface to volume ratio, a large hydrostatic pressure is being exerted on the NCs by which the crystalline lattices are strained and the effects can be observed in their optical properties. PL is red shifted in case of strained large NC and blue shifted for strained small NCs [10] along with a large blue shift in absorption too. Furthermore, at low temperature, different thermal contraction [11] between a substrate and NC thin film on it, affects the PL properties due to differential strain at low temperature [12,13]. However, the NC growth conditions are such t...

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