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Page 45
Nano Research & Applications
ISSN: 2471-9838
Advanced Nanotechnology 2019
EuroSciCon Conference on
Advanced Nanotechnology
I
n this paper, we conduct a first trial to study the dependence of photoluminescence (PL) emission, and optical absorption edge
of Zn
0.78
Cd
0.22
S quantum dots on thermally induced - poly to single crystalline structural phase transition and morphological
changes, along with excitation wavelength. It is found that, increasing annealing temperature (Ta) results in two structural
phase transitions: firstly, from polycrystalline cubic to crystalline hexagonal Zn
0.78
Cd
0.22
S structures at Ta 500
o
C, secondly,
from polycrystalline cubic to single crystalline predominant ZnO hexagonal structure at 600
o
C, accompanied by an increase
in XRD peaks intensity, sharpness, the crystallite size, the reduction of the internal local strain and the dislocation density, and
consequently red shift of the optical gap. In addition, analysis of HRTEM images and SAED patterns, FTIR and Raman spectra
indicates good agreement with XRD results. Moreover, the deconvoluted PL emission spectra at excitation wavelength 325 nm
of the as-prepared and annealed nanoparticles up to 500
o
C demonstrate UV- blue emission bands at 362, 395, 443, and 523 nm,
which quenched and red shifted to 402, 469, 509, 540 nm with increasing ex to 370 nm, along with the evolution of new emission
bands at 594, 637, and 685 nm. In addition, the as-synthesized Zn
0.78
Cd
0.22
S colloidal solution at ex of 325 nm reveals multiple
broad emission bands associated with quenching and red shift in the PL intensity with increasingex to 370 nm. Increasing Ta
up to 500 oC at ex of 370 nm results in quenching and red shift of the overall PL spectra, whereas at ex of 325 nm, no change
is observed. Moreover, Zn
0.78
Cd
0.22
S nanopowder at either 600 or 700 oC at ex 370 nm reveal new and red shifted PL emission
bands, along with a drastic increase in PL intensity by one order of magnitude higher than that observed at ex 325 nm. The
unusual excitation wavelength dependent enhancement and blue shift of PL in Zn
0.78
Cd
0.22
S nanopowder has demonstrated.
Trapping and recombination radiative levels have been identified and the corresponding energy band diagrams are suggested.
prof.m_osman@aun.edu.egInfluence of Thermally Induced Poly to Single
Crystalline Structural Phase Transition on
Photoluminescence and Optical Absorption
behavior of Zn0.78Cd0.22S Quantum Dots for
Photo electronic applications
M. A. Osman, A. G. Abd-Elrahim
Physics Department, Faculty of Science, Assiut University
Nano Res Appl 2019, Volume:5
DOI: 10.21767/2471-9838-C2-034