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

Well-resolved luminescence from the crystal-held level H-2(2)(9/2) a Gamma( 8) at 36236 cm(-1) to 34 lower levels has been observed for Cs2NaErCl6 upon pulsed laser excitation at 273.9 nn. The assignments enable the location a nd identification of the upconversion luminescence state in the study of Ha san et nl. [Phys. Rev. B 56, 4518 (1997)] and support a two-photon vibronic excitation mechanism in the latter case. The experimentally determined ene rgy for the H-2(2)(9/2) a Gamma(8) state differs considerably from the calc ulated value. The temporal behavior of blue upconverted luminescence from t he (2)G(9/2) state is reproduced from an analytical expression, and it is s hown that the alternative fitting procedure does not enable the two-ion upc onversion rate W to be well determined. [S0163-1829(99)13143-6].