Spectroscopic properties of Nd3+ in MgAl2O4 spinel nanocrystals

Highlights: ► Synthesis of the nanocrystalline powders of magnesium aluminate (MgAl2O4) spinel doped with neodymium(III) ions by modified Pechini synthesis. ► Spectroscopic-quality parameter values are above 3 for all samples. ► The 4F3/2 → 4I9/2 transition of neodymium dominates in emission spectra in spinel lattice. ► Very effective cross relaxation rate indicates rapid donor–donor transfer. - Abstract: Nd3+ doped MgAl2O4 spinel nanocrystals have been prepared by the sol–gel method. Their size decreases from 12 to 7 nm with increasing Nd3+ concentration from 0.1 to 5%, respectively. Some crystal field components of the Nd3+ energy levels in MgAl2O4 spinel were found from the 300 K reflectance absorption and the 77 K emission spectra. The 4F3/2 → 4I9/2 transition dominates in the emission spectra and accordingly spectroscopic-quality parameter (SQP) is equal to 3.3 for all samples. Decay time of the emission from the 4F3/2 level in MgAl2O4:Nd3+ (0.1%) nanocrystals is equal to 90 μs, and decreases with increasing neodymium concentration due to very efficient cross-relaxations. The slope of cross-relaxation rate is close to 2 which indicates fast donor–donor transfer.