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CHAPTER 6
SUMMARY AND SUGGESTIONS FOR FUTURE WORK
6.1 SUMMARY
Growth of high quality single crystals from aqueous solution with fewer
defects is one of the very important techniques in the optical industry involving
the production of large crystals. As the growth process is closer to room
temperature, this technique results in the formation of high quality crystals for
device applications. Materials having moderate solubility can be grown by low
temperature solution growth method by slow evaporation technique. In the recent
years, growth of a metal organic single crystals play a vital role in nonlinear
optical applications due to high laser damage threshold, stronger physiochemical
stability and high second order nonlinear optical property.
Optical properties of the semiorganic materials make them suitable for
optical switching devices, optical data storage technology and laser fusion
experiments. Zinc tris thiourea sulphate (ZTS) is a well known semiorganic
nonlinear optical material, which is popular for nonlinear optical applications. The
thesis deals with synthesis, growth and characterizations of 1 mole % and
2 mole % potassium iodide (KI), sodium chloride (NaCl), glycine (C2H5NO2) and
magnesium sulphate (MgSO4) doped ZTS single crystals were grown from
solution growth method especially slow evaporation technique at room
temperature. Grown crystals were characterized by various characterizations
studies like powder X-ray diffraction studies, Fourier transform infrared studies,
UV-Visible studies, micro hardness studies, TGA/DSC studies, EDX analysis and
SHG studies.
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The lattice parameters of the Pure, 1 mole % and 2 mole % potassium
iodide (KI), sodium chloride (NaCl), glycine (C2H5NO2) and magnesium sulphate
(MgSO4) doped ZTS single crystals were calculated by using powder X-ray
diffraction studies. The grown pure and doped crystals belong to orthorhombic
system with space group Pca21 and the crystallinity was confirmed by well defined
sharp peaks of powder X-ray diffraction pattern. It is clearly inferred for XRD
pattern of doped crystals that the lattice parameters are slightly varied due to
addition of KI, NaCl, C2H5NO2 and MgSO4 and at the same time the total crystal
system was not altered from the original orthorhombic system. The presence of
functional groups and modes of vibrations were identified by Fourier transform
infrared studies. The FTIR spectrum of 1 mole % and 2 mole % of KI, NaCl,
C2H5NO2 and MgSO4 doped ZTS crystals showed that the slight shift in the
characteristic vibrational frequencies compared with pure ZTS which may be due
to the incorporations of dopants in ZTS single crystals.
The estimated band gap of the grown Pure, 1 mole % and 2 mole % of KI,
NaCl, C2H5NO2 and MgSO4 doped ZTS crystals are 4.184 eV, 4.20 eV, 4.246 eV,
4.32 eV, 4.36 eV, 4.465 eV, 4.374 eV, 4.185 eV and 4.199 eV respectively. These
results confirmed that the Pure and doped materials belong to the category of
typical insulating materials. The as grown pure, 1 mole % and 2 mole % of KI,
NaCl, C2H5NO2 and MgSO4 doped ZTS crystals are found to be thermally stable
up to 236.92˚C, 238.77˚C, 242.52˚C, 237.12˚C, 238.64˚C, 239.08˚C, 238.83˚C,
241.07˚C and 241.53˚C and decomposition starts only after this stability level. All
the grown crystals have good thermal stability which was studied by TGA. The
thermal stability of the materials clearly indicates that it can be exploited for
nonlinear optical applications up to stable temperature. 2 mole % of KI doped ZTS
crystal possesses high melting point and second harmonic generation efficiency.
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Mechanical properties of the grown crystals were studied by using
HMV-2T model Vicker’s microhardness tester. Microhardness studies confirmed
that the grown crystals belong to the category of soft materials and hence it is
concluded that the crystals prove to be a good engineering material for second
harmonic generation device applications and laser fusion experiments. The
elemental compositions of the grown pure and doped ZTS crystals were measured
by EDX analysis.
6.2 SUGGESTIONS FOR FUTURE WORK
A semiorganic Pure, 1 mole % and 2 mole % of KI, NaCl, C2H5NO2 and
MgSO4 doped ZTS crystals were grown from low temperature solution growth
method by slow evaporation technique at room temperature and the grown crystals
were characterised by various studies such as Powder X-ray diffraction, Fourier
transform infrared (FTIR) studies, UV absorbance and Transmittance studies,
Vicker’s microhardness studies, Thermo gravimetric analysis and Differential
scanning calorimetry (TGA/DSC) studies, EDX analysis, SHG studies and the
results have been elucidated in this thesis. All the grown crystals possess
promising NLO properties. Zinc tris thiourea sulphate (ZTS) single crystals is a
potential nonlinear optical material for generation of green light by doubling the
frequency of Q switched Nd-YAG laser. The KI doped ZTS crystals were found to
have better properties. Zinc tris thiourea sulphate (ZTS) single crystals doped with
other metal ions and amino acids can be tried and their properties can be
compared. Attempts can be made to optimize the growth parameters to improve
the atmospheric stability.
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