  Morphology plays a crucial role in deciding the chemical and optical
properties of nanomaterials due to confinement effects. We report the
morphology transition of colloidal molybdenum disulfide (MoS$_2$)
nanostructures, synthesized by one pot heat-up method, from mix of quantum dots
(QDs) and nanosheets to predominantly nanorods by varying the synthesis
reaction temperature from 90 to 160 degree C. The stoichiometry and composition
of the synthesized QDs, nanosheets and nanorods have been quantified to be
MoS$_2$ using energy dispersive X-ray spectroscopy and X-ray photoelectron
spectroscopy analysis. Nanostructure morphology transition due to variation in
reaction temperature has resulted in photoluminescence quantum yield
enhancement from zero to 4.4% on increase in temperature from 90 to 120 degree
C. On further increase in temperature to 160 degree C, a decrease in quantum
yield to 2.63% is observed. A red shift of 18 nm and 140 nm in the emission
maxima and absorption edge respectively is observed for the synthesized
nanostructures with increase in reaction temperature from 90 to 160 degree C.
The change in the quantum yield is attributed to the change in shape and hence
confinement of charge carriers. To the best of our knowledge, first-time
microscopic analysis of colloidal MoS$_2$ nanostructures shape and optical
property variation with temperature explained by non-classical growth mechanism
is presented.
