Tuning structural and optical characteristics with Mn2+ introduced into ZnAl2O4:Cr3+ nanophosphors: Energy transfer process and cations rearrangement

Cr3+/Mn2+ co-doped ZnAl2O4 (ZAO) phosphors were synthesized by using common sol-gel method. The crystallinity and particle morphology of the product samples were analyzed by using X-ray diffraction and scanning electron microscope. The atomic occupation was characterized by using X-ray photoelectron spectroscopy, indicating that the inversion defects were absent with Mn2+ entering the spinel lattices. The characteristic red quintuplets of Cr3+ were observed in singly doped ZAO phosphors, and became dual emissions at 685 nm and 690 nm with 1 nm of full width at half maximum in Mn2+/Cr3+ co-doped ZAO phosphors. The energy transfer from Mn2+ to Cr3+ was present with 96% of energy transfer efficiency. Mn2+ ions reduced the inversion defects and enhanced the electrons transition probability related to R line. The maximum enhancement factor of red emission was about 70. The CIE suggested that the co-doped samples exhibited yellow emissions with blue light (427 nm) excitation. ZAO:Mn2+,Cr3+ phosphors are proved to be promising candidates for red laser and white LED driving with green light.