Origin of visible and near IR upconversion in Yb3+-Tm3+-Er3+ doped BaMgF4 phosphor through energy transfer and cross-relaxation processes

Near infrared and green, red emission through upconversion and energy transfer processes in BaMgF4 doped with Yb3+-Tm3+ and Yb3+-Tm3+-Er3+ excited at 980 nm were investigated. The BaMgF4:Yb3+,Tm3+ phosphor showed a dominating UC emission at 800 nm. The origin of this 800 nm emission peak was explored through different possible cross-relaxation processes. The optimized composition of Yb3+ and Tm3+ was further co-doped with Er3+, these compositions also showed dominating 800 nm emission for lower concentrations of Er3+ which was gradually suppressed at higher Er3+ concentration. The enhancement of the visible emission of Er3+ in the BaMgF4:Yb3+,Tm3+,xEr3+ doped phosphor suggests the efficient energy transfer from Yb3+ to Tm3+ and Tm3+ to Er3+. By tuning the concentrations of the dopants, a near white light emission under infrared excitation was also achieved. © 2019 Elsevier B.V