The study investigates the electronic properties of ultrathin molybdenum disulfide (MoS₂) crystals with varying numbers of monolayers (N = 1, 2, ..., 6). Using optical spectroscopy techniques such as absorption, photoluminescence, and photoconductivity, the researchers trace the effect of quantum confinement on the material's electronic structure. As the thickness decreases, the indirect band gap shifts upwards in energy by more than 0.6 eV, leading to a crossover to a direct-gap material in the single monolayer limit. Unlike the bulk material, the monolayer MoS₂ exhibits strong light emission, with a luminescence quantum efficiency (LQY) increase of over 1000 compared to the bulk. The PL spectra and absorption spectra show distinct features for monolayer and few-layer samples, with the monolayer PL peak at 1.90 eV matching the lower absorption resonance. Photoconductivity measurements further confirm that monolayer MoS₂ is a direct-gap material, while few-layer samples are indirect-gap semiconductors. These findings highlight the unique electronic properties of ultrathin MoS₂ and its potential applications in photostable markers, sensors, photocatalysis, and photovoltaics.The study investigates the electronic properties of ultrathin molybdenum disulfide (MoS₂) crystals with varying numbers of monolayers (N = 1, 2, ..., 6). Using optical spectroscopy techniques such as absorption, photoluminescence, and photoconductivity, the researchers trace the effect of quantum confinement on the material's electronic structure. As the thickness decreases, the indirect band gap shifts upwards in energy by more than 0.6 eV, leading to a crossover to a direct-gap material in the single monolayer limit. Unlike the bulk material, the monolayer MoS₂ exhibits strong light emission, with a luminescence quantum efficiency (LQY) increase of over 1000 compared to the bulk. The PL spectra and absorption spectra show distinct features for monolayer and few-layer samples, with the monolayer PL peak at 1.90 eV matching the lower absorption resonance. Photoconductivity measurements further confirm that monolayer MoS₂ is a direct-gap material, while few-layer samples are indirect-gap semiconductors. These findings highlight the unique electronic properties of ultrathin MoS₂ and its potential applications in photostable markers, sensors, photocatalysis, and photovoltaics.