Self-reduction Of Mn And Valence-control Of The Luminescence Of Mn²⁺/Mn⁴⁺

Transition metal/rare earth ions doped inorganic luminescent materials have been widely applied in the fields of illumination,displays and optical communications,etc.Their luminescent properties are not only related to the crystal structure and composition of the hosts,but also highly associated with the valence state of the doping ions.To obtain the luminescence of active ion with lower valence states,reducing atmosphere is always required to realize the control of valence state.However,some low-valenced rare earth ions RE²⁺ can be obtained through the abnormal self-reduction possess of RE3+?RE²⁺ in air in some specific hosts.At present,the research about this phenomenon is away focused on lanthanide ions especially Eu,while little attention has been paid to transition metal like Mn.Thus in this dissertation,the self-reduction of Mn and the valence control of Mn²⁺/Mn⁴⁺ in some selected germanates and aluminates were investigated in detail.The main research results of this dissertation are as follows:?1?Zn₂GeO₄:Mn phosphors were prepared by the traditional high temperature solid state reaction method in air.The luminescence of green emissions in 536 nm originated from the 4T1?4G??6A1?6S?transition of Mn²⁺ were obtained even with the variation of doping concentrations,Mn sources and synthetic temperatures.The Mn⁴⁺/Mn7+?Mn²⁺ self-reduction phenomenon can be confirmed based on photoluminescence spectra,EPR and XPS.This abnormal phenomenon was explained by the charge compensation mechanism and defects in view of the composition and crystal structure of Zn₂GeO₄ as well as the properties of Mn itself.In addition,this phenomenon can be extended to other germanates like A2BGeO4:Mn?A=Li,Na;B=Zn,Mg?.We also discussed the long-persistent luminescence properties of Zn₂GeO₄:Mn prepared with different Mn sources,and put forward the possible relevant mechanism.?2?Mn doped hexaaluminate Ba0.75Al11O17.25 samples containing both AlO4 tetrahedrons and AlO6 octahedrons were prepared by high temperature solid-state reaction process with different Mn sources,Mn concentrations and atmospheres,all of which exhibited 512 nm green emissions of Mn²⁺,even if the sample was prepared with Mn O2 in pure oxygen atmosphere.Thus Ba0.75Al11O17.25 was proved to be an appropriate host for Mn self-reduction,which can be can be attributed to the Reidinger defects in itself.The valence control of Mn²⁺/Mn⁴⁺ in Ba0.75Al11O17.25 could be regulated by the change of solid solution composition from Ba0.75Al11O17.25 to BaMgAl10O17,which could be explained by the variation of defects in the hosts.As for the composition BaMgAl10O17 with no Reidinger defects in view of crystal structure,the self-reduction of a small number of Mn ions was related to the defects formed in the high temperature preparation process.