Granular phosphors are commonly used in several applications in biomedical imaging and instrumentation. The structural and optical properties of phosphor materials affect the optical signal transferred out and play a critical role in the quality of the final signal or image. In recent years, following developments in materials science and technology, several new methods have been successfully implemented for the preparation of nanosized phosphors. It is of interest to investigate whether nanophosphors could replace existing micro phosphors for next generation high-performance displays and imaging devices. The purpose of the present study was to investigate the variation of the optical parameters (e.g. light extinction coefficient mext, probability of light absorption p, light anisotropy factor g) in the sub-micron and nano scale under the variability of light wavelength (400-700 nm) and refractive index (e.g., two limiting values were used 1.4 and 2.0). For the case of low refractive index (1.4), by increasing the grain diameter: (a) the light extinction increases, (b) the light absorption probability decreases and (c) the anisotropy factor increases in the whole range or gran sizes (2-1000 nm). However, for the high value of the refractive index (2.0), the light extinction coefficient was found to increase up to a maximum for grain diameter: (a) 200 nm (at 400 nm light wavelength) and (b) 600 nm (at 700 nm light wavelength). Finally, at 400 nm grain diameter, the probability of light absorption was found to decrease down to a minimum while the anisotropy factor was found to increase up to maximum for all light wavelengths considered.