Upconversion phenomena in the Yb3+ doped transition metal compounds Rb2MnCl4 and CsMnBr3

Crystals of Yb3+ doped Rb2MnCl4 and CsMnBr3 show orange–red Mn2+ 4T1g→6A1g upconverted luminescence under near-infrared Yb3+ excitation. By short 10 ns pulse excitations the upconversion (UC) process for both compounds has been determined to consist of a sequence of ground and excited-state absorption steps. This mechanism can gain nonzero probability by assuming an exchange mechanism between Yb3+ and Mn2+. The efficiency of the UC process is dependent on the structural nature of the Yb3+–Mn2+ connection. It is three orders of magnitude more efficient in Rb2MnCl4 : Yb3+ with a corner-sharing Yb3+–Cl–Mn2+ arrangement than in the face-sharing Yb3+–Br3–Mn2+ arrangement of CsMnBr3 : Yb3+.