Experimental and theoretical studies on luminescent mechanisms and different visual color of the mixed system composed of MgGeO3:Mn, Eu and Zn2GeO4:Mn

摘要

In this work, the mixed system composed of Zn2GeO4: Mn and MgGeO3: Mn, Eu was synthesized by the high temperature solid phase method. Under the external excitation, visual color of samples was yellow. However, after the excitation was completed, visual color turned to be red. From luminescence spectrum, it was found that Zn2GeO4: Mn emitted green fluorescence of 534 nm under the excitation of 375 nm light. At the same time, MgGeO3: Mn, Eu emitted both fluorescence and persistent luminescence (PersL) of 668 nm. Moreover, the properties of PersL present samples were superior to other red PersL materials. Fine band structures from density functional theory (DFT) indicated that there were different luminescent mechanisms of Zn2GeO4: Mn and MgGeO3: Mn, Eu. When Zn2GeO4: Mn was excited, electron transitioned from VB to CB directly. Through CB, the electron was captured by the 4T2(D) of Mn ion, then the electron jumped from T-4(2)(D) to VB and recombined at once with the previous hole and emitted a 534 nm photon. When MgGeO3: Mn, Eu was excited, electron transitioned from (6)A(1)(S) of Mn ion to CB and left a hole. Through CB, electron was captured by F-7(6) levels of Eu3+ and remained metastable for a long time, which slowed down the recombined rate between electron and hole. Under thermal stimulation, the captured electron returned to CB from F-7(6) levels and was recaptured by the T-4(2)(D) of Mn. The electron transitioned down toward (6)A(1)(S) and recombined with the hole immediately, then emitted a photon with 668 nm.