Green and red light emission by upconversion from the near-IR in Yb3+ doped CsMnBr3

Direct near-IR excitation of Yb3+ F-2(7/2)-->F-5/2 levels at 10126, 10138, and 10596 cm(-1) in CsMnBr3:0.5%Yb3+ leads to three types of luminescence at cryogenic temperatures: near-IR Yb3+ emission and green and red upconverted luminescence. The green luminescence around 20000 cm(-1) is identified as cooperative Yb3+ pair upconversion. The broad red upconversion luminescence band centered at 14700 cm(-1) is ascribed to the T-4(1g)--> (6)A(1g) transition of Mn2+. Pulsed measurements indicate a sequence of ground-state absorption and excited-state absorption steps. for the red upconversion process. One- and two-color excitation experiments support this, and we conclude that the red upconversion occurs by an exchange mechanism involving Yb3+ and Mn2+. The Yb3+ F-2(5/2)-->F-7/2 near-IR emission around 10000 cm(-1) is also observed after Mn2+ excitation at 21838 cm(-1). This is indicative of a Mn2+ T-4(1g)--> Yb3+ F-2(5/2) relaxation process, which is a potential loss process for upconversion efficiency.