Efficient down- and up-conversion of Pr 3+–Yb 3+ co-doped transparent oxyfluoride glass ceramics

Abstract

Pr 3+ and/or Yb 3+ doped transparent oxyfluoride glass ceramics (GCs) containing CaF 2 nanocrystals were fabricated and characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Judd–Ofelt (J–O) intensity parameters, radiative transition probability, radiative lifetimes, and branching ratios of Pr 3+ have been calculated from the absorption spectra. Upon 470 nm excitation, Pr 3+ doped GCs yield intense visible-near infrared (NIR) luminescence corresponding to the 3P 0 → 3H 6, 3P 0 → 3F 2,3,4, 3P 1 → 1G 4, 1D 2 → 3H 5, and 1D 2 → 3F 4 transitions, respectively. With the addition of Yb 3+ ions, NIR down-conversion (DC) emissions at 976 nm ( 2F 5/2 → 2F 7/2) were achieved, due to efficient energy transfer (ET) from Pr 3+ to Yb 3+. Underlying mechanism for the NIR-DC is analyzed in terms of static and dynamic photoemission and monitored excitation spectra. The maximum quantum efficiency from Pr 3+: 3P 0 to Yb 3+: 2F 5/2 is calculated to be 153%. In comparison, intense up-conversion emissions at 489, 545, 606, and 651 nm have been obtained in Pr 3+–Yb 3+ codoped glass and GCs under 980 nm excitation, which is ascribed to be two-photon involved ET from Yb 3+ to Pr 3+.