Downconversion in Cs 2 NaErCl 6

The room temperature downconversion emission of Er 3+ in the low phonon energy, low band-gap host Cs2NaErCl6 upon synchrotron radiation excitation is rationalized. Energy transfer cross-relaxation schemes are proposed following the interpretation of the vacuum ultraviolet and ultraviolet excitation and emission spectra. The highest energy emission from Er 3+ occurs from the 2 I11/2 multiplet term (� 40600 cm � 1 ). The behaviour of Er 3+ in Cs2NaYCl6:Er 3+ is also discussed and interpreted.