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+ 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.