  The sensitive correlation between optical parameters and strain in Mo$S_2$
results in a totally different approach to tune the optical properties.
Usually, an external source of strain is employed to monitor the optical and
vibrational properties of a material. It is always challenging to have a
precise control over the strain and its consequences on material properties.
Here, we report the presence of a compressive strain in Mo$S_2$ crystalline
powder and nanosheets obtained via the process of ball-milling and probe
sonication. The diffraction peaks in the X-ray diffraction pattern shift to
higher 2$\theta$ value implying a compressive strain that increases with the
processing time. The absorption spectra, photoluminescence and Raman modes are
blue-shifted w.r.t the bulk unprocessed sample. The observed blue-shift is
attributed to the presence of compressive strain in the samples. Whereas in
thin nano-sheets of Mo$S_2$, it is very likely that both quantum confinement as
well as strain result in the observed blue-shift. These results indicate that
by optimizing the processing conditions and/or time, a strain of desired amount
and hence tunable shift in optical properties of material can be achieved.
