Size-dependent structural phase transitions and their correlation with photoluminescence and optical absorption behavior of annealed Zn0.45Cd0.55S quantum dots

Journal Article · Mon Oct 15 00:00:00 EDT 2018 · Materials Characterization

DOI:https://doi.org/10.1016/J.MATCHAR.2018.07.020· OSTI ID:22805792

Abd-Elrahim, A. G.; Othman, A. A. ^[1]

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1. Physics Department, Faculty of Science, Assiut University, Assiut 71515 (Egypt)

Highlights: • Thermal Induced Structural Phase transition in nanostructured Zn{sub 0.45}Cd{sub 0.55}S. • Low temperature structural phase transition from cubic to hexagonal structure. • Thermal annealing effect on FTIR and Raman Spectra. • Thermal annealing effect on optical absorption of Zn{sub 0.45}Cd{sub 0.55}S nanoparticles. • Excitation-wavelength dependent photoluminescence emission spectra. - Abstract: In this paper, we investigate the effect of thermally induced structural phase transitions on the photoluminescence (PL) and optical absorption behaviour of Zn{sub 0.45}Cd{sub 0.55}S nanoparticles (NPs). Analysis of X-ray diffraction (XRD) patterns and high-resolution electron microscope (HRTEM) images reveal that the as-synthesized sample possesses zinc-blende-type cubic structure. In addition, at annealing temperature (T{sub a}) 400 °C, the cubic structure transforms completely into the wurtzite-type hexagonal structure. Furthermore, the second phase transition of the as-synthesized sample has observed at 700 °C, where the cubic structure has transformed into mixed polycrystalline phases of hexagonal ZnO, cubic CdO, monoclinic CdSO{sub 3}, and orthorhombic ZnSO{sub 4} structures. These new phases have also confirmed from the analysis of Raman and FTIR spectra. Analysis of UV–visible optical absorption spectra demonstrates that Increasing T{sub a} results in the decrease of optical band gap due the improvement in crystallinity accompanied by the increase in the particle size. The PL emission bands at an excitation energy of 3.818 eV exhibit redshift and a decrease in the intensity with increasing T{sub a} up to 500 °C. Meanwhile, further increase in T{sub a} up to 700 °C results in the enhancement of green emission intensity. On the other hand, PL emission spectra at 3.354 eV and T{sub a} 700 °C, reveal a dramatic increase in the emission intensity nearly by one-order of magnitude with respect to its value of the as-synthesized sample. This behaviour is ascribed to the incorporation of oxygen-related defects via thermal annealing in air, which act as additive radiative centers. Also, we have interpreted the observed spectral blue shift of PL emission spectrum with increasing excitation energy.

• OSTI ID: 22805792
• Journal Information: Materials Characterization, Vol. 144; Other Information: Copyright (c) 2017 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 1044-5803
• Country of Publication: United States
• Language: English

Related Subjects

77 NANOSCIENCE AND NANOTECHNOLOGY
ABSORPTION
ABSORPTION SPECTRA
ANNEALING
CADMIUM COMPOUNDS
CRYSTAL STRUCTURE
CRYSTAL-PHASE TRANSFORMATIONS
EMISSION SPECTRA
FOURIER TRANSFORMATION
INFRARED SPECTRA
NANOPARTICLES
PHOTOLUMINESCENCE
POLYCRYSTALS
QUANTUM DOTS
RAMAN SPECTRA
RAMAN SPECTROSCOPY
RED SHIFT
SULFUR COMPOUNDS
TRANSMISSION ELECTRON MICROSCOPY
X-RAY DIFFRACTION
ZINC COMPOUNDS