Upconversion and downconversion photoluminescence and optical limiting in colloidal MoS2 nanostructures prepared by ultrasonication

Nano structures of MoS2 are trending up as a smart optoelectronic material nowadays. Photoluminescence, linear and non-linear optical properties of highly crystalline MoS2 quantum dot (QD)-nano flake (NF) colloidal dispersion in de-ionized water prepared by cost effective mechanical grinding assisted bath ultrasonication and centrifugation is reported in this article. Particle size, which varies with the sonication time and centrifuging speed, is confirmed by TEM and dynamic light scattering (DLS) analysis. The absorbance spectra show characteristic A, B, C and D excitonic transitions of NFs and high energy E peaks of QDs. MoS2 QD-NF dispersion exhibits appreciable photon upconversion and down conversion photoluminescence (PL) that are applicable to solar cells. The photoluminescence emission red shifts with red shift in excitation wavelength. Time correlated fluorescence decay measurement estimates the life time and it varies with the particle size. Raman spectra of spin coated MoS2 dispersion confirm the hexagonal structure and formation of few layered MoS2 in-plane (E12g) and out-of-plane (A1g) vibrational modes. Selective area diffraction patterns confirm the crystallinity and hexagonal nature of the grown nanostructures. Non-linear optical studies of the samples exhibit reverse saturable absorption (RSA) which is applicable to optical limiting devices.