Comment on 'Energy transfer and upconversions in cubic Cs2NaYCl6:Er+3 and Cs2NaErCl6'

Abstract

Well-resolved luminescence from the crystal-field level 2H(2)9/2 aΓ8 at 36236 cm-1 to 34 lower levels has been observed for Cs2NaErCl6 upon pulsed laser excitation at 273.9 nm. The assignments enable the location and identification of the upconversion luminescence state in the study of Hasan et al. [Phys. Rev. B 56, 4518 (1997)] and support a two-photon vibronic excitation mechanism in the latter case. The experimentally determined energy for the 2H(2)9/2 aΓ8 state differs considerably from the calculated value. The temporal behavior of blue upconverted luminescence from the 2G9/2 state is reproduced from an analytical expression, and it is shown that the alternative fitting procedure does not enable the two-ion upconversion rate W to be well determined.