Optimizing Cr^(3+) concentration and evaluating energy transfer from Cr^(3+) to Nd^(3+) in Cr,Nd:GGG nanocrystals prepared by sol-gel method

Nanopowder of Cr：GGG and nanopowder of Cr,Nd：GGG with different concentrations of Cr3＋ ranging from 0.1 at.% to 1.5 at.% were synthesized by the sol-gel method using acetic acid and ethylene glycol. Thermal gravimetric analysis and differential scanning calorimetry （TGA-DSC）, X-ray diffraction （XRD） and photoluminescence spectroscopy were used to characterize the powder. The crystallite size was about 58 nm when treated at 1000 oC for 2 h. Cr3＋ photoluminescence spectrum in GGG showed a broad band emission around 730 nm. The intensity of this band decreased when co-doped with Nd, indicating an efficient energy transfer from Cr3＋ to Nd3＋. Photoluminescence intensity of Nd in Cr,Nd：GGG at 1.06μm showed that the optimum concentration of Cr3＋ was about 1 at.% （more or less） for 1 at.% Nd3＋. This result was also confirmed by chromium fluorescence decay rate analysis. Energy transfer efficiency was found to be about 84% for 1 at.% concentration of each chromium and neodymium.