Modulation of radiative defects in MgAl2O4 nanocrystals probed using NMR, ESR, and PL spectroscopies

We have investigated the influence of combustion fuels on radiative defects of MgAl 2O 4 spinel. Monoethanolamine (MEA), glycine, and urea fuels were employed to synthesize three samples of MgAl 2O 4 nanocrystals, choice consequence of which has been observed on cation inversion and various intrinsic defects. Synchrotron powder x-ray diffraction patterns were refined by the Rietveld method. All samples exhibited a spinel structure, with a minor secondary phase of MgO in the sample synthesized by urea fuel. 27Al nuclear magnetic resonance (NMR) inferred the distribution of Al cations among tetrahedral and octahedral sites with structural distortion of interstices. Rietveld, NMR, and diffuse reflectance spectra analyses revealed the presence of antisite defects, cation, and anion vacancies, which may be anticipated to induce F(Mg) defect centers through charge compensation. An electron spin resonance (ESR) study was carried out to investigate the paramagnetic defect centers. Two prominent broad ESR signals, attributed to F + and V - defect centers, originated from the delocalization of paramagnetic spins and their interaction with nearby cations. Photoluminescence studies further confirmed the existence of F(Mg) defect centers, VO-related defects, and Mg Al '</mml:msubsup> and V Mg ''</mml:msubsup> defects in all samples. It was found that the nature of the defects did not change, but the concentration of defects varied significantly with the type of fuel employed and excitation wavelength. The MgAl 2O 4 samples synthesized using glycine, urea, and MEA fuels were found to be rich in F(Mg) defect centers, VO-related defects, and Mg Al '</mml:msubsup>, V Mg '', <mml:msub> V O-related defects, respectively. The tailoring of defect-assisted photoluminescence by varying fuel types in MgAl <mml:msub> 2O <mml:msub> 4 spinel can be exploited in various luminescence applications.