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

In nominally 2% Cr5+ and 10% Er3+ co-doped YVO4, a highly efficient nonradiative energy transfer Cr5+ B-2(2) --> Er3+ I-4(13/2) 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+ Al-2 --> E-2 excitation, nonradiative E-2 to B-2(2) relaxation, energy transfer to Er3+ I-4(11/2) and finally excited state absorption processes on Er3+ I-4(13/2) --> S-4(3/2) F-4(7/2), H-2(11/2). In addition, Er3+ I-4(11/2), --> Cr5+ B-2(2) energy transfer occurs. The pathway through Cr5+ B-2(2) leads to an enhanced nonradiative relaxation rate from the Er3+ I-4(11/2) to the laser relevant I-4(13/2) energy level. The rate constants of the energy transfer processes are estimated. (C) 2002 Elsevier Science B.V. All rights reserved.