  Rare-earth (Yb/Gd) complexes with neutral organophosphorus ligands are
briefly discussed for their application in liquid scintillation technique. To
evaluate the principle feasibility of a high rare-earth loaded scintillator,
the ytterbium chloride complexes with tri-isoamylphosphine oxides were
synthesized. Relative scintillation efficiency (RSE) for two Yb concentrations
(78 and 88 g/L) was measured by means of the internal conversion electron
exitation from Cs-137. The results obtained were 50 and 40% respectively.
