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layered structure with a hexagonal unit cell. It is a highly suitable in
the development of active matrix flat panel imagers (AMFPIs)
which can be used as detectors for X-ray digital radiography using
direct conversion technique, mammography energy range detec-
tion [14e19] in which the X-ray photons are directly converting in
to electronic charge. The other applications of titled material is in
photoconductors, photo-detectors, photovoltaic, co-precipitation
sensors, biological labeling and diagnostic, LEDs including photo
electro co-precipitation solar cells, etc. applications [20]. There are
several reports available in the literature on the synthesis and
fabrication of nanostructures and thin films of PbI2using different
techniques and study their structural, vibrational, optical, dielectric
and electrical properties and shows a great change in the properties
[18,21e29]. Therefore in the current work the authors aim is to
fabricate the nanostructures of PbI2 with well-defined morphology
using different techniques such as co-precipitation at room tem-
perature, hydrothermal and microwave irradiation at low temper-
ature (i.e. 140 ꢀC). It is well know that the microwave technique
delivers homogenous internal and volumetric heating at rapid rates
[30,31] and found to be better than conventional heating. The
fabricated nanostructures have been studied for different proper-
ties such as structural, vibrational, optical and dielectric properties
and compared the obtained results with the existing literature. As a
result we found that microwave irradiation technique is a better
choice other techniques to fabricate the nanorods of the titled
material.
2.2. Characterization techniques
To perform the structural analysis of the synthesized nano-
structures of PbI2 we have recorded the powder X-ray diffraction
(PXRD) patterns using a Shimadzu X-600 Japan powder X-ray
diffractometer (PXRD) having CuKa radiation (40 kV, 30 mA,
l
¼ 0.1543 nm) at the scan rate of 0.02ꢀ/m over the angular range of
5ꢀ ꢁ 2
q
ꢁ 90ꢀ at room temperature. Surface topography of the all
the synthesized nanostructures were examined using scanning
electron microscope (JSM 6360 LA, Japan) equipped with energy
dispersive analytical X-ray unit (EDXS). Before subjecting to SEM
analysis, the samples were sputter coated with 10 nm of platinum
to eliminate charge build up. FT-Raman spectroscopic measure-
ments were carried out to study the vibrational modes/functional
groups of PbI2 nanostructures. In this measurement the laser beam
was made to incident normally on the surfaces of the specimens to
record the spectrum and scattered intensity was collected at room
temperature using THERMO SCIENTIFIC, DXR FT-RAMAN coupled
with microscope using full range grating (3500e100 cmꢂ1). The
used laser power was 0.2 mW (532 nm laser), at estimated reso-
lution 5.1e8.3 cmꢂ1 and the size of the aperture pinhole was kept
50 mm. The UVeVis spectroscopic measurement was done at room
temperature of all synthesized nanostructures of PbI2 in methanol
media on a JASCO V-570 UVeViseNIR spectrophotometer. Using
the recorded data the various optical parameters were calculated.
Using a Shimadzu UVeVis.-NIR spectrophotometer (model UV-
3600),the diffuse reflectance (DR) was recorded in the wide
wavelength range by using an integrating sphere attachment. The
photoluminescence (PL) spectra were recorded for all the prepared
PbI2 nanostructured samples at room temperature under the same
conditions using a Lumina fluorescence spectrometer (Thermo
Fisher Scientific) in the wavelength range of 280e480 nm. The
spectral bandwidth is variable as 0.5, 1.0, 2.5, 5.0, 10, 20 nm for both
excitation and emission monochromators and in the current work
it was chosen 1 nm for emission monochromator. The dielectric
measurements were carried out for all the prepared nanostructures
of PbI2 by making the pallets of similar thickness. The prepared
samples were coated with 10 nm of platinum on both the sides
using a sputter system before subjecting to measurement. The
dielectric constant, loss and ac conductivity were studied in higher
frequency range of 1 kHze10 MHz at room temperature using a
KEITHLEY 4200-SCS system.
2. Experimental
2.1. Synthesis of PbI2 nanostructure
For the synthesis of PbI2 nanostructures we have used all the
reagents of analytical grade of high purity purchased from Alfa
Aesar in the experiment. For the synthesis of PbI2 we have taken
1 M lead acetate (39.987 g) and 50 ml of double distilled water,
50 ml CTAB and 50 ml of PVA in one beaker step by step and 2 M
Sodium Iodide (37.795 g) was dissolved in 50 ml double distilled
water in another beaker and both the solutions were homoge-
neously dissolved at room temperature using highly stable mag-
netic stirrer fixed at 500 rpm. After getting the transparent solution
we have mixed them very slowly in one beaker and stirred
continuously and clear yellow solution was obtained which is
recognized as lead iodide (PbI2). Further the finally prepared so-
lution was divided in three parts one as received and other two for
hydrothermal and microwave irradiation process respectively. One
portion of the resultant product was subsequently transformed in
to a Teflon lined autoclave with a stainless steel shell for hydro-
thermal process and in Teflon vessel for microwave process. The
temperature of the autoclave was maintained at 145 ꢀC for 24 h and
then cooled to room temperature naturally. ANTON PARR Micro-
wave was used to irradiate the samples under fixed power at
800 W, the temperature of the microwave was programmed as rise
in 15 min up to 145 ꢀC and keep constant at the same temperature
for 15 min then cooled in 30 min. The clear yellow products was
obtained by all three techniques which were washed many times
with double distilled water and filtered and dried in vacuum at
75 ꢀC for5 h.The reaction mechanism involved in this experiment is
described in Figure 1S (see supplementary data).
3. Results and discussion
3.1. Structural analysis
The recorded powder X-ray diffraction (PXRD) patterns of the
synthesized nanostructures of PbI2are shown in Fig. 1. It is clear
from the sharpness of the patterns that the synthesized nano-
structures are highly crystalline in nature. The recorded PXRD data
was used as input in POWDERX software and cell parameters were
calculated and the single phase was confirmed. The refined cell
values (Table 1) were found to be of Hexagonal phase of PbI2 pre-
pared by all methods which are in good agreement with the earlier
reported value JCPDS-07-0235.The indexed XRD pattern shows that
it is of a 2H-polytype of PbI2 and also very minute deviation is
observed from that. As clear from Fig. 1 that the presence of 111, 113
and 203 very low intensity reflections indicates a minute amount of
4H-polytype presence as well. No peak due to impurity such as
PbOHI and Pb(OH)2was observed which reveals the high purity of
the synthesized nanostructures of the product.
It is well known in the literature that the reaction media play a
key role in the synthesis of nanostructure materials under hydro-
thermal conditions as well as in microwave process. We have used
CTAB and PVA both as reaction media/surfactants in order to con-
trol the morphology of nanostructures and found that a compact
and perfect structure of PbI2 has been obtained in every process.
The crystallite size of the fabricated PbI2 nanorods was evalu-
0:9l
ated by using Scherer's formula; D ¼
where, the average
b cos q
crystallite size, X-ray wavelength (1.54056 Å) and full width at half