Luminescence and excitation spectra of Cr3+:MgAl2O4 nanoceramics

The effect of the applied sintering pressure on luminescence and excitation spectra of Cr3+ doped MgAl2O4 nanoceramics was investigated. It was found that the intensity of 2E → 4A2 phosphorescence decreased significantly when pumped directly into 4T1 band. The effect was extremely strong for nanoceramics sintered at higher pressures. Moreover, the intensity of 4A2 → 4T1 band in excitation spectra drastically decreased with sintering pressure compared to 4A2 → 4T2 band. This behavior was related to trigonal distortion of Oh symmetry of Cr3+ ion which increases with decreasing the size of nanocrystals resulting in enhancement of the 4T1 → 4T2 nonradiative pathway due to decrease of ΔE (4T1, 4T2) energy gap.