Fotoluminescência no infravermelho da cerâmica galato de magnésio dopada com cromo trivalente

Polycrystalline MgGa2O4 samples doped with Cr3+ are investigated by luminescence and excitation spectroscopy at 4.2 K, 77 K and room temperature. In the spectra we observe photoluminescence bands in red and near infrared spectral regions, associate to the 2E(2G)® 4A2(4F) and 4T2(4F)® 4A2(4F) electronic transitions of trivalent chromium ions in octahedral sites.  The luminescence spectra of  the MgGa2O4 with 1% of Cr3+ present narrow peaks in the higher energy region and some structures on a wide band in the lower energy region.  The peaks are attributed to the spin forbidden 2E(2G)® 4A2(4F) electronic transition and the broad bands are associates to the spin allowed 4T2(4F)®4A2(4F) electronic transition of  Cr3+ in octahedral sites. In the emission spectra narrow lines appear at high energy region and are attributed to the presence of the b-Ga2O3:Cr3+ compound. The excitation spectra show two broad bands. The lower energy band is identified with the 4A2(4F)® 4T2(4F) while the higher energy  band is associated to 4A2(4F)®4T1(4F) electronic transition. From the excitation bands energy positions we calculate the crystal field Dq = 1780 cm-1 and Racah B = 630 cm-1 and C = 2820 cm-1 parameters. The results show that the material presents both high and intermediate crystal-fields for these ions.