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

Crystals of Yb3+ doped Rb-2 MnCl4 and CsMnBr3 show orange-red Mn2+ T-4(1g) --> (6)A(1g) 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+-Br-3-Mn2+ arrangement of CsMnBr3 : Yb3+. (C) 2001 Elsevier Science B.V. All rights reserved.