Structural defect-induced white light emission from synthetic Zn-rich trioctahedral smectite

Abstract

In this research work, AlIII substituted by MgII and ZnII atoms in smectites (Sm) of the formula [Na0.7Mg2.5-xZnxLi0.3Si4O10(OH)2] were synthesized. Its structural and intrinsically highly photoluminescent (PL) properties were reported. The complex distributions of MgII and ZnII atoms were observed in both octahedral and tetrahedral sites in the synthesized Sm (as evident with XRD, XPS, and ESR studies). The visible white light emission was observed when excited with UV light (250 nm). The observed strong photoluminescence (PL) was attributed to the electronic transition from oxygen vacancy to acceptor atoms induced by isomorphous substitution in both tetrahedral and octahedral sites (MgAl′,MgSi′′,ZnAl′,ZnSi′′). With introduction of ZnII atom, there was an increase in MgAl′andMgSi′′defects energy levels that resulted in bathochromic shifts in VO∙∙→MgAl′′, VO∙∙→MgSi′′ and VO∙∙→VO emission lines. Moreover, two additional emission lines in blue and red-light regions were observed due to two new ZnAl′,ZnSi′′ defect centers that led to VO∙∙→ZnAl′ and VO∙∙→ZnSi′′ electronic transitions.