RELAXATION OF THE S-4(3 2) LEVEL OF ER3+ IN CS2NAERCL6/

Octahedral (O-h) symmetry of the RE(3+) sites in the Cs(2)NaRECl(6) cr ystals removes all of the electric dipole intensity from the 4f-4f tra nsitions. Thus the decay of luminescence originating in the excited st ates of RE ions is governed by phonon assisted (vibronic) transitions, multiphonon relaxation and phonon assisted energy transfer (cross rel axation and energy migration to impurities). Contribution of these pro cesses to the decay of the S-4(3/2) State of erbium in CS2NaErCl6 has been studied in the 4.2-300 K temperature region. It has been conclude d that at low temperatures the S-4(3/2) state decays exclusively by vi bronic transitions. At about 100 K the cross relaxation via the I-4(9/ 2) state becomes operative. Efficiency of this process grows strongly with increasing temperature, reducing the S-4(3/2) lifetime by almost three orders of magnitude. No evidence has been found that multiphonon relaxations contribute to the decay of the S-4(3/2) state.