Investigations of Mn,
Ni, Fe and Pb
doped zinc sulphide
nanoparticles
A thesis submitted to the
FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY IN Physics
Pramod H. Borse
Department
of Physics
Pune 411 007
December,
1999
Prof. A.W. Joshi Prof.(Mrs.) S.K. Kulkarni P.H.Borse
Head of the Department Research
Guide Research Student
Center for Advanced Studies in Materials Science and
Department of Physics,
There is a growing interest in the semiconductor nanoparticles for
the past few years. Semiconductor nanoparticles also known as semiconductor
clusters or quantum dots form a special class of new materials for
which size dependent properties are observed. Size dependent properties occur
when the size of the particles is comparable or smaller than Bohr radius of exciton for that material. For most of the semiconductors
the Bohr radius is few nanometers. Therefore nanoparticles of interest are in
the span of a few nanometers. Synthesis and physico-chemical characterization
of nanoparticles is therefore considered to be a difficult task as analytical
methods for the bulk material often fail in case of nanoparticles. Nevertheless
due to their novel optical and electronic properties observed so far, many
groups have undertaken research programmes on
nanoparticles all over the world.
In my Ph.D. thesis, work on undoped zinc sulphide
and Mn, Fe, Ni and Pb doped
zinc sulphide nanoparticles was carried out. There
are large number of methods now to synthesize nanoparticles with some
advantages and disadvantages. A chemical method, has
been adopted in this work i.e. the zinc sulphide
nanoparticles in the size range of 1 to 5 nm are stabilized using organic
molecules. Advantages of this method are relative simplicity, inexpensiveness,
short synthesis time etc. whereas disadvantages are low thermal
stability and need of depositing on some substrate if they are to be used in making
some device. This forms then another step. However due to strearic
hinderance offered by the organic molecules, the
particles do not coalesce to form bigger molecules. However characterization of
nanoparticles is quite a difficult task, Therefore several techniques need to
be judiciously employed in order to unambiguously understand their properties.
Various techniques like UV absorption spectroscopy, X-ray diffraction,
photoluminescence, atomic absorption spectroscopy, electron spin resonance and
photoelectron spectroscopy have been used in this work. Particles are
stabilized using organic molecules. The molecules used in the synthesis have a thiol group at one end, which interacts with zinc sulphide perhaps through the sulphur
end. Thermal stability of the particles has been investigated. The organically
capped particles are found to be stable even above 573 K. When some metal ions
are incorporated fluorescence is known to occur in different regions of visible
spectrum producing violet, green, yellow, red etc. light. Different colour shades and brightness also can be obtained. This
makes zinc sulphide a widely used phosphor material.
Here an attempt was made to see how doped nanoparticles will behave. Thus
effect of dopants, their concentration, synthesis parameters etc. has
been thoroughly investigated and their effect on luminescence properties
studied. In case of manganese doped zinc sulphide an
attempt is made to give a model about effect of manganese concentration on
photoluminescence. Quenching effect due to iron and nickel dopants has been
observed and discussed to some extent. Effect of lead doping also has been
investigated to a good length. All these results are presented in the thesis in
view of the current interest.
Pramod H. Borse