Photoluminescence and multiphonon resonant Raman scattering in low-temperature grown ZnO nanostructures

Abstract

The authors report on the optical properties of nanocrystalline ZnO grown at 200°C by radio-frequency magnetron sputtering. The nanocrystalline nature of the films was confirmed by cross-sectional transmission electron microscopy. In these films, ZnO nanocrystals with an average size of about 3–5nm were embedded in an amorphous matrix. The photoluminescence spectra from such nanostructured thin films show the near-band-edge emissions around 3.3eV. A redshift of about 8–11cm−1 is observed in the case of first-order longitudinal-optical (LO) phonon of ZnO in such nanostructures when compared to the LO phonon peak of bulk ZnO. The ultraviolet resonant Raman excitation at 77K shows multiphonon LO modes up to eighth order.

Resonant Raman scattering of ZnS, ZnO, and ZnS/ZnO core/shell quantum dots

“…A large number of periodical peak repetitions is attributed to multiple-phonon Raman scattering (up to ninth order) and indicates the very high crystalline quality of the fabricated nanostructures. To the best of our knowledge, multiphonon LO modes in ZnO QDs were observed up to eighth order at low temperature (77 K) while a strong band edge free excitonic photoluminescence near 4000 cm −1 prevents the observation of multiphonon modes at room temperature [12]. In our case, this photoluminescence is suppressed most probably by defect states at the QD surfaces as well as by minimization of laser excitation power and spectrometer slits.…”

“…Most of the published data on the phonon spectra of QDs by a variety of fabrication methods were obtained by Raman scattering. Optical and surface optical phonon modes as well as multiphonon modes in CdS, PbS, CuS, and Ag 2 S QDs were observed in a number of resonant and non-resonant Raman experiments [3,4,6,12].…”

“…Therefore the knowledge of the phonon spectra of nanomaterials is of a great importance. Several experimental techniques including methods of the wet chemistry [3][4][5] or combination of evaporation techniques with wet chemistry [6], colloidal chemistry [7][8][9], preparation of QDs in polymer matrices [10], sputtering techniques [11,12], and sol-gel methods [13] are known to be used for the formation of ZnS and ZnO QDs. Among those the Langmuir-Blodgett (LB) technique is considered as a versatile, relatively simple, fast, and low-cost method for QD fabrication of II-VI and IV-VI materials with controllable QD areal density on different substrates [14][15][16][17][18].…”

Visible emission characteristics from different defects of ZnS nanocrystals

“…The appearance of the multiple Resonance Raman peaks indicates that these ZnS samples have a large value of Huang-Rhys parameter and a good optical quality. 39,40 Electron-phonon coupling is an important issue in semiconductor materials, because it has significant influence on the optical and electrical properties of semiconductors, such as the phonon replicas of excitons and the energy relaxation rate of excited carriers in the luminescence spectra. The 2LO/1LO ratio is the parameter to specify the strength of the electronphonon interaction.…”

Novel Fork Architectures of Ag₂S Nanoparticles Synthesized through <i>In Situ</i> Self-Assembly inside Chitosan Matrix

“…4(a), spectral deformation band at 3400 cm -1 for the OH -groups, convoluted peak at 2900 cm -1 for the -CH 2 backbone, 1650-1690 cm -1 for the amide I (C=O) bands, there is another convoluted spectral peak at around 1650 -1550 cm -1 ,which are assigned to amine (-NH 2 ), convoluted The fundamental and overtone modes correspond to these vibrations match well with vibrations of low temperature α-Ag 2 S phase [35]. The observation of multiple resonant Raman peaks indicates that the yielded Ag 2 S nanoparticles possess good optical quality [39] and good crystalinity [40].…”