Design, synthesis and mechanism of green afterglow phosphors Zn4B6O13:Mn2+ doped with Ln3+ (Ln = Sm, Yb, Eu) guided by VRBE

In this work, the construction of host referred binding energy (HRBE) diagram and vacuum referred binding energy (VRBE) diagram is described in detail. The energy gap of Zn 4 B 6 O 13 is calculated by diffuse reflectance spectroscopy and the energy level positions of Eu 3+ in VRBE are determined by the charge transfer (CT) band of Zn 4 B 6 O 13 doped Eu 3+ to construct a complete lanthanide ions VRBE diagram. According to the constructed VRBE of Zn 4 B 6 O 13 system, novel long-afterglow phosphors Zn 4 B 6 O 13 :Mn 2+ co-doped with Ln 3+ (Ln = Sm, Yb, Eu) is designed and synthesized successfully. The influence of B 2 O 3 contents on the crystal structure and luminescence of the Mn 2+ doped zinc borate phosphors were analyzed by XRD and emission spectra. Photoluminescence excitation and emission spectra, persistent luminescence spectra and afterglow decay curve indicate that the doping of lanthanide ions Sm 3+ and Yb 3+ prolonged the afterglow duration of green emission of Mn 2+ effectively. The fitting results of persistent luminescence spectra is consistent with the fast decay process of afterglow decay curve. The energy level depths of Sm 3+ and Yb 3+ traps obtained by thermoluminescence analysis are 0.49 eV and 1.12 eV respectively, which are in good agreement with the results calculated by VRBE. The energy level position of Sm 3+ and Yb 3+ below the conduction band (CB) are suitable trap depth, which can store and release electrons continuously. However, that of Eu 3+ is too deep to enhance the afterglow. According to the VRBE theory, the mechanism of the electron trap is satisfactorily explained, which is important to the subsequent research of system design and mechanism explanation of lanthanide ions doped long afterglow materials. • The VRBE diagram is constructed using the PLE spectrum of Zn 4 B 6 O 13 :Eu 3+ and the DRS data of Zn 4 B 6 O 13 . • According to the guidance of VRBE, the implantation of Sm 3+ and Yb 3+ enhances the afterglow emission in Zn 4 B 6 O 13 :Mn 2+ . • The mechanism of introducing suitable trap to enhance afterglow is consistent with the theoretical design of VRBE.