Abstracts 2004

Abstract of Publication No. 487

Pascal Gerner, Christine Reinhard and Hans U. Güdel
Cooperative Near-IR to Visible Photon Upconversion in Yb3+-Doped MnCl2 and MnBr2: Comparison with a Series of Yb3+-Doped Mn2+ Halides
Chem. Eur. J. 10, 4735-4741 (2004)      Full Text (PDF)      DOI-Link     

Abstract: Yb3+-doped MnCl2 and MnBr2 crystals exhibit strong red upconversion luminescence under near-infrared excitation around 10000 cm1 at temperatures below 100 K. The broad red luminescence band is centred around 15200 cm1 for both compounds and identified as the Mn2+ 4T1g6A1g transition. Excitation with 10 ns pulses indicates that the upconversion process consists of a sequence of ground-state and excited-state absorption steps. The experimental VIS/NIR photon ratio at 12 K for an excitation power of 191 mW focused on the sample with a 53 mm lens is 4.1% for MnCl2:Yb3+ and 1.2% for MnBr2:Yb3+. An upconversion mechanism based on exchange coupled Yb3+-Mn2+ ions is proposed. Similar upconversion properties have been reported for RbMnCl3:Yb3+, CsMnCl3:Yb3+, CsMnBr3:Yb3+, RbMnBr3:Yb3+, Rb2MnCl4:Yb3+. The efficiency of the upconversion process in these compounds is strongly dependent on the connectivity between the Yb3+ and Mn2+ ions. The VIS/NIR photon ratio decreases by three orders of magnitude along the series of corner-sharing Yb3+-Cl-Mn2+, edge-sharing Yb3+-(Cl)2-Mn2+ to face-sharing Yb3+-(Br)3-Mn2+ bridging geometry. This trend is discussed in terms of the dependence of the relevant super-exchange pathways on the Yb3+-Mn2+ bridging geometry.

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