Strong blue emission from Ti-doped MgAl2O4 crystals

Strong blue emission was observed from Ti-doped spinel crystals. We conclude that Ti ion is located at B-site with D3d symmetry as Ti4+ from the optical and electron spin resonance measurement. The charge-transfer excitation and deexcitation between O2--Ti4+ and O--Ti3+ ion pairs are assigned to these optical absorption and emission processes.