We have studied the spectroscopic properties of four nano-powder samples of Y3Al5O12: Cr particles with diameters ranging from 28 nm to 250 nm. For each sample we have measured accurately the emission spectrum in a wide range of temperatures ranging from 30 to more than 600 K. The spectra generally consisted of the R-lines narrow spectral emission and of the accompanying vibronic side-bands. We noted the increase of the vibronic emission intensity with respect to the R-line intensity going from the larger to the shorter diameter powders. For each sample we have also measured the decay patterns of the excited Cr ions following a pulsed excitation. These measurements were conducted in the same temperature range (30-600 K) in order to fully characterize the samples examined.