We report on organic-inorganic nanocomposites with combined properties of quantum cutting and down shifting of solar UV spectrum. They cut a single high energy UV photon of solar radiation in two near-IR (NIR) low energy photons and use the energy of the UV photon to produce low energy visible photons. The applications include solar spectrum down-convertors and luminescent solar concentrators (LSCs). The nanocomposites were made of organic hosts filled the nanoparticles of Lanthanide doped fluoride phosphor NaYF4:Yb3+, Er3+. As an organic host for the nanoparticles in an LSC simulator 1-Propanol was used. The particles of the synthesized phosphor powder were ball-milled to an average size of~ 200-nm. The LSC filled with the phosphor nanocolloid produced 130% more electric power than in case of pure 1-Propanol. This effect was not observed when the LSC was illuminated with an incandescent light bulb with no UV component in its radiation spectrum. The LSC performance was thus due to down shifting and quantum cutting of the UV spectral component of solar radiation by the phosphor nanoparticles into visible and NIR radiation matching the spectral response of the silicon PV solar cells. The results are of interest for green solar power.