30
T. B. Asafa et al.
associated with radiative recombination of charge carriers. This means that the electrons in the valence band (VB) receive sufficient energy to transfer to the conduction
band (CB) whenever light of sufficient energy (longer or equal wavelength to its
band gap) irradiated on it (Giahi et al. 2019). Therefore, emission of energy as PL
radiation occurs when electrons go back from CB to VB. As evident from Fig. 9a,
a strong peak is identified around 356 nm that can be attributed to band–to–band
transition (Giahi et al. 2019). The inset indicates the deconvoluted spectrum for pure
TiO 2 nanoparticles. The small emission noticed at 341 nm could be attributed to
the recombination of electrons–holes in surface defects or surface oxygen vacancies (Shariatzadeh and Moradi 2014). The emission of intermediate band transition
observed in titania could be seen as a shoulder peak at 370 nm. It is observed that
intensity of the peak becomes higher with the increase of the Mg dopants amount.
The room temperature emission PL spectrum of ZnO nanopowder excited at
235 nm is shown in Fig. 9b. It has emission peaks in blue region around 407 nm and
broad blue region around 484 nm. The emission peak at 407 nm emanates from the
recombination of free excitons through an exciton–exciton collision process or due to
intrinsic defects such as oxygen and zinc interstitials (Taunk et al. 2015). The broad
blue emission band at 484 nm is usually attributed to the radiative recombination of a
photo-generated hole with an electron occupying the oxygen vacancy (Shariatzadeh
and Moradi 2014). The possible cause of the visible emission in the ZnO has been
attributed to surface state of the nanomaterials (Taunk et al. 2015). However, it is
accepted that the PL emission is caused by the recombination of excited electrons
and holes, and the lower PL intensity may imply the lower recombination rate of
electrons and holes under light irradiation.
1.5 X-ray Diffraction (XRD) Technique
X-ray diffraction (XRD) is one of the powerful techniques extensively used for
determination of crystal structure, grain size, nature of crystalline phase, and lattice
parameters for nanoparticles based on X-ray radiation (Mourdikoudis et al. 2018).
These high-energy (100 eV–100 keV) radiations are generated when a focused electron beam accelerated across a high voltage field bombards a stationary or rotating
solid target. They penetrate deep into a given material and give information about the
structural arrangement of atoms and molecules (Cullity and Stock 2001). The lattice
parameters of nanomaterials are evaluated by employing the Scherrer equation using
the broadening of the most intense peak from the XRD data. The diffraction angle
and intensity of the peaks of the XRD pattern are then compared to the available data
from Joint Committee on Powder Diffraction Standards (JCPDS, presently known
as the International Center for Diffraction Data, ICDD) database. Common targets
used in X-ray tubes include Cu and Mo, which emits 8 and 14 keV X-rays with
corresponding wavelengths of 1.54 Å and 0.8 Å, respectively.
X-rays primarily interact with electrons in atoms, and during the course of interaction, some photons from the incident beam will be reflected away or diffracted
T. B. Asafa et al.
associated with radiative recombination of charge carriers. This means that the electrons in the valence band (VB) receive sufficient energy to transfer to the conduction
band (CB) whenever light of sufficient energy (longer or equal wavelength to its
band gap) irradiated on it (Giahi et al. 2019). Therefore, emission of energy as PL
radiation occurs when electrons go back from CB to VB. As evident from Fig. 9a,
a strong peak is identified around 356 nm that can be attributed to band–to–band
transition (Giahi et al. 2019). The inset indicates the deconvoluted spectrum for pure
TiO 2 nanoparticles. The small emission noticed at 341 nm could be attributed to
the recombination of electrons–holes in surface defects or surface oxygen vacancies (Shariatzadeh and Moradi 2014). The emission of intermediate band transition
observed in titania could be seen as a shoulder peak at 370 nm. It is observed that
intensity of the peak becomes higher with the increase of the Mg dopants amount.
The room temperature emission PL spectrum of ZnO nanopowder excited at
235 nm is shown in Fig. 9b. It has emission peaks in blue region around 407 nm and
broad blue region around 484 nm. The emission peak at 407 nm emanates from the
recombination of free excitons through an exciton–exciton collision process or due to
intrinsic defects such as oxygen and zinc interstitials (Taunk et al. 2015). The broad
blue emission band at 484 nm is usually attributed to the radiative recombination of a
photo-generated hole with an electron occupying the oxygen vacancy (Shariatzadeh
and Moradi 2014). The possible cause of the visible emission in the ZnO has been
attributed to surface state of the nanomaterials (Taunk et al. 2015). However, it is
accepted that the PL emission is caused by the recombination of excited electrons
and holes, and the lower PL intensity may imply the lower recombination rate of
electrons and holes under light irradiation.
1.5 X-ray Diffraction (XRD) Technique
X-ray diffraction (XRD) is one of the powerful techniques extensively used for
determination of crystal structure, grain size, nature of crystalline phase, and lattice
parameters for nanoparticles based on X-ray radiation (Mourdikoudis et al. 2018).
These high-energy (100 eV–100 keV) radiations are generated when a focused electron beam accelerated across a high voltage field bombards a stationary or rotating
solid target. They penetrate deep into a given material and give information about the
structural arrangement of atoms and molecules (Cullity and Stock 2001). The lattice
parameters of nanomaterials are evaluated by employing the Scherrer equation using
the broadening of the most intense peak from the XRD data. The diffraction angle
and intensity of the peaks of the XRD pattern are then compared to the available data
from Joint Committee on Powder Diffraction Standards (JCPDS, presently known
as the International Center for Diffraction Data, ICDD) database. Common targets
used in X-ray tubes include Cu and Mo, which emits 8 and 14 keV X-rays with
corresponding wavelengths of 1.54 Å and 0.8 Å, respectively.
X-rays primarily interact with electrons in atoms, and during the course of interaction, some photons from the incident beam will be reflected away or diffracted