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

Temperature-Dependent Photoluminescence and Energy-Transfer Dynamics in Mn 2+ -Doped (C 4 H 9 NH 3 ) 2 PbBr 4 Two-Dimensional (2D) Layered Perovskite

Reported here are the low-temperature photoluminescence (PL), energy-transfer mechanism, and exciton dynamics of Mn 2+ -doped two-dimensional (2D) perovskites that show interesting differences from their three-dimensionally doped counterpart. Dopant emission in 2D system shows increased PL intensity and shortened lifetime with increase of temperature and strong dopant emission even at low temperatures. Transient absorption (TA) spectroscopy reveals the dominant role of "hot" excitons in dictating the fast energy-transfer timescale. The operative dynamics of the generated hot excitons include filling up of existing trap states (shallow and deep) and energy-transfer channel from hot excitons to dopant states. Global analysis and target modeling of TA data provide an estimate of excitons (hot and band edge) to a dopant energy-transfer timescale of 330 ps, which is much faster than the band edge exciton lifetime (2 ns). Such fast energy-transfer timescale arises due to enhanced carrier exchange interaction resulting from higher exciton confinement, increased covalency, and involvement of hot excitons in the 2D perovskites. In stark contrast to three-dimensional systems, the high energy-transfer rate in 2D system results in high dopant emission intensity even at low temperatures. Increased intrinsic vibronic coupling at higher temperatures further supports efficient Mn 2+ sensitization that ultimately dictates the observed temperature dependence of the dopant emission (intensity, lifetime). © 2019 American Chemical Society