THE LUMINESCENCE OF EUROPIUM IN STRONTIUM BORATES

At 300 K the Eu2+ ion luminesces efficiently in SrB4O7, and to a lesse r extent in SrB6O10 and Sr3B2O6. In the last compound the lowest 4f-5d absorption band is at extremely low energy for Eu2+. Due to this and a large Stokes shift, the EU2+ emission band has its maximum at 590 nm . From a comparison with the luminescence of Ce3+ and Pb2+ in this lat tice it is concluded that a strong non-cubic crystal field splits the 5d excited state, causing the lowest f-d absorption transition to be a t a low energy position. In SrB2O4 and Sr2B2O5 only Eu3+ was found. An explanation for this is proposed on the basis of a charge-compensatio n mechanism for Eu3+; the luminescence of this ion is discussed as wel l.