The cubic system Cs2NaEr(NO2)6 provides an interesting comparison with the corresponding hexachloroelpasolite, having a similar structure but, in addition, there are high frequency phonons present since the one phonon spectrum extends up to 1 600 cm-1. The absorption spectrum at low temperatures shows a beautiful progression in the NO2 bending mode in the near UV in addition to the typical f-f erbium centered transitions. Under red excitation at 80 K into the 4I15/2 yields 4F9/2 transition strong, but short lived emission is observed from both the 4F9/2 and 4I9/2 states. At high irradiation densities intense emission is also observed in the blue at 21 460 and 21 280 cm-1 and at other wavenumbers in the UV and green regions. These emissions have different complex decay curves and appear to arise from energy migration to defect sites followed by up- conversion at those sites. In the up-conversion process, the luminescent defect sites are destroyed but appear to regenerate on long term storage of the crystals at room temperature.
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