Optical spectroscopy of the Nd3+ and Nd3+-Gd3+/Yb3+ centres in BaF2 single crystals and calculations on lanthanide-doped BaF2

Absorption and site-selective laser spectroscopy of BaF2 single crystals homogeneously doped with Nd3+ ions as well as heterogeneously doped with Nd3+ and either Gd3+ or Yb3+ ions, performed at 10 K, is presented. In each case a single centre, assigned to be of C3v symmetry, is dominant. A heterogeneous Nd3+-RE3+ (RE being either Nd or Yb) is also present in each of the double doped crystals. Energy levels for six multiplets of the single Nd3+ centre and for three multiplets for each Nd3+-RE3+ centre are presented together with the 4F3/2 (R) multiplet fluorescence lifetime for each centre. Calculations give comparable solution energies for C3v and C4v symmetry Nd3+ centres in BaF2; the C3v symmetry configuration has lower energy for the preceding lanthanides while C4v is favoured from Sm3+ onwards.