  In present study, Tetragonal Mn$_3$O$_4$ thin films of different coating
layers of 2, 4, 6, 8, and 10 were prepared on the microscopic glass slides by
the spin-coating method. X-ray diffraction, Raman spectroscopy, and
ultra-violet visible spectroscopy were used to explore the structural and
optical properties of Mn$_3$O$_4$ thin films. XRD patterns and Raman spectra
confirm the phase of all films as tetragonal. The average crystallite size of
films increased from ~17 to ~25 nm with increasing coating layers. Optical
properties such as band gap, skin depth, cutoff wavelength, excitation
coefficient, refractive index, etc, have been studied in detail by using
ultra-violet visible spectroscopy. The direct optical band gap and refractive
index of fabricated films were decreased as increasing the coating layers of
Mn$_3$O$_4$. The refractive index for 2 and 4 coating layers were decreased as
increasing the incident wavelength. While for 6, 8, and 10 coating layers, the
values of refractive index remain constant with respect to incident wavelength.
The optical analyses suggest that prepared Mn$_3$O$_4$ thin films can be used
as a potential candidate for optical semiconductor devices including
photovoltaic cells and optical sensors.
