In this masters project, the literatures survey of pure chromium oxide and aluminum (Al) doped chromium (III) oxide (Cr2O3) nanoparticles are summarized. The band gap and crystal size are determined by the Brus equation, the input values are the experimental values in the literature survey The experimental band gap energy in range 3.48 to 1.90 eV, the calculated average crystal size for these doped materials is in the range of 13.84 to 7 nm. And the calculated energy band gap ranges 3.59 to 2.09 eV. The absorption peak readings of UV- Vis spectrometer is on the range of 248nm to 308nm wavelength, the calculated values of the optical band gap are 5eV to4.02Ev.