title: "Energy Relay Center" for doped mechanoluminescence materials: a case study on Cu-doped and Mn-doped CaZnOS.
abstract: We unraveled the mechanisms of transition metal-doped mechanoluminescent materials through a case study of CaZnOS. We found that the native point defect levels in Cu or Mn-doped CaZnOS system acted as energy relay centers for luminescence energy transfer. In combination with native point defect levels, discussed in a previous study [Phys. Chem. Chem. Phys., 2016, 18, 25946], we found that phosphor luminescence belongs to two different mechanisms. For Cu-doping, it occurs by the path via the conduction band minimum to the Cu-t2glevel of the 3d orbital localized in the band gap. The hole-drifting effect was found to support the reported red-shifting of the emission. Both reversible and irreversible mechanical quenching were attributed to the spatially separated electrons recombining with the hole localized on the Cu-t2glevel within the gap at levels below or above respectively. For Mn-doping, this occurs by a collaborative luminescence assisted by native point defects, and the excited states of Mn2+overlap with the conduction band edge. The coexistence of MnZnand MnCawas confirmed, but was relatively low in MnCa. The concentration quenching effect, as well as the red-shift of absorption, shows a strong correlation with native point defect levels and the relative position of the 4T1(4G) state for both MnZnand MnCa. Further simplified approximations were used for modeling such concentration quenching effects.
authors.affiliation: Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SAR, China. bhuang@polyu.edu.hk.
authors.forename: Bolong
authors.identifier: http://orcid.org/0000-0002-2526-2002
authors.initials: B
authors.lastname: Huang
authors.affiliation: Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing 100083, P. R. China. cfpan@binn.cas.cn.
authors.forename: Dengfeng
authors.initials: D
authors.lastname: Peng
authors.affiliation: Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing 100083, P. R. China. cfpan@binn.cas.cn.
authors.forename: Caofeng
authors.initials: C
authors.lastname: Pan