Optical properties of strictly monolayer MoS2 films, which are grown on c-sapphire substrates using microcavity based CVD route, have been investigated by temperature dependent absorption and temperature as well as excitation intensity dependent photoluminescence (PL) spectroscopy. Our study reveals a high intensity broad luminescence band appearing at similar to 1.7 eV along with the usual free exciton/trion peak (similar to 1.86 eV). The investigation furthermore attributes this broad transition to excitons bound to two types of defects, whose binding energies are found to be similar to 11 and similar to 118 meV. Integrated intensity of this feature decreases with the increase in the impinging sulfur flux during growth and by post-growth annealing in sulfur atmosphere suggesting that these defects must be related to sulfur deficiency. Interestingly, exciton-phonon coupling for these defect bound excitons is found to be much stronger than that is associated with free excitons/trions. (C) 2018 Elsevier B.V. All rights reserved.