Nanocrystalline Lu3Sc2Ga3O12 garnet powders doped with different concentrations of trivalent ytterbium (Yb3+) ions have been prepared by sol-gel method. These garnet nano-powders have been characterized for their structural and luminescence properties using X-ray diffraction, diffuse reflectance and luminescence spectra. Near-infrared and blue cooperative upconversion luminescence spectra and decay curves of Yb3+ ions in these nano-garnets have been measured as a function of the optically active ion concentration. Quenching of near infrared and cooperative luminescence intensity beyond 5.0 mol% of Yb3+ ion concentration have been observed. Variation of blue cooperative luminescence intensity with pump power has also been discussed.