Pascal Gerner

Broad-band Cr5+-sensitized Er3+ luminescence in YVO4

Abstract In nominally 2% Cr5+ and 10% Er3+ co-doped YVO4, a highly efficient nonradiative energy transfer Cr5+ 2B2→Er3+ 4I13/2 is active, which is competitive with the multiphonon relaxation of Cr5+. A new type of near-infrared-to-visible upconversion process is identified. It consists of a Cr5+ 2A1→2E excitation, nonradiative 2E to 2B2 relaxation, energy transfer to Er3+ 4I13/2 and finally excited state absorption processes on Er3+ 4I13/2→4S3/2, 4F7/2, 2H11/2. In addition, Er3+ 4I11/2→Cr5+ 2B2 energy transfer occurs. The pathway through Cr5+ 2B2 leads to an enhanced nonradiative relaxation rate from the Er3+ 4I11/2 to the laser relevant 4I13/2 energy level. The rate constants of the energy transfer processes are estimated.

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

Abstract Crystals of Yb 3+ doped Rb 2 MnCl 4 and CsMnBr 3 show orange–red Mn 2+ 4 T 1 g → 6 A 1 g upconverted luminescence under near-infrared Yb 3+ 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 Yb 3+ and Mn 2+ . The efficiency of the UC process is dependent on the structural nature of the Yb 3+ –Mn 2+ connection. It is three orders of magnitude more efficient in Rb 2 MnCl 4 : Yb 3+ with a corner-sharing Yb 3+ –Cl–Mn 2+ arrangement than in the face-sharing Yb 3+ –Br 3 –Mn 2+ arrangement of CsMnBr 3 : Yb 3+ .