A novel Mn(II)-based green phosphor and its self-reduction mechanism

A novel Mn2+ doped Li2CdSiO4 phosphors were synthesized in 1100 degrees C without reducing atmosphere. Their structure, self-reduction mechanism and luminescence properties were evaluated. Oxygen vacancies were confirmed to exist in Li2CdSiO4 by electron spin-resonance spectroscopy and bond volume polarizability of Li2CdSiO4 was calculated to prove the lattice oxygen (O3) may easily form oxygen defect (V-o(center dot)). After different valence Mn source (MnO2 and MnCO3) as raw materials were built into Li2CdSiO4, similar emission bands with a maximal value of 515 nm appeared under 226 nm excitation and it was ascribed that energy transfer occurred from host to Mn2+ ions. Meanwhile, it was demonstrated that a series of redox reactions does happen from MnCO3 to Mn3O4 with increasing calcination temperature. Eventually, Mn-3 (+) (Mn3O4) ions were reduced to Mn2+ through electron transfer from V-o(center dot) to Mn3+. Furthermore, interstitials oxygen (O-i) was detected in Li2CdSiO4: 0.02Mn sample through X-ray photoelectron spectroscopy (XPS) and the special tunnel structure may provide a suitable position to stabilize Oi in air. Direct spectroscopic evidence and the assumed mechanism have been presented for explaining these processes. This research provides a new perspective for defects induced Mn2+ emission in designing broad band green phosphors. More importantly, the present work further deepens the understanding of the self-reduction mechanism of Mn2+.