Optical emission spectra of chromium doped nanocrystalline zinc gallate

Optical emission spectra of nanocrystalline zinc gallate (ZnGa2O4) and trivalent chromium ion doped zinc gallate (ZnGa2O4:Cr3+) are reported for different concentrations of the dopant ion. The measurements have been carried out over the temperature range between 77 and 296 K. The emission spectrum of nanocrystalline ZnGa2O4 shows two broad peaks. The intensity variation in these peaks, with temperature, is indicative of the effect of symmetry breaking in the electronic band structure of ZnGa2O4 in nanocrystalline samples. In addition, we find that the relative intensities of the sharp spectral lines of Cr3+ in nanocrystalline ZnGa2O4:Cr3+) are quite different from those reported for corresponding bulk samples. The spectral profiles of the so-called R1, R2, N1, and N2 lines have also been studied. The data are analyzed using crystal field theory, which includes an exchange interaction between the nearest neighbor Cr3+ pairs in ZnGa2O4. We estimate the exchange parameters for Cr3+ in nanocrystalline ZnGa2O4:Cr3+) Though, in the literature, there exist reports on optical properties of the corresponding bulk spinel, our approach and consequent results on nanocrystalline ZnGa2O4: Cr3+ are not only interesting from the physics point of view but also can be of use in nanotechnology. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3224866]