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2014-06-24T03:16:55+05:30
The colour of lanthanide ions due to f-f transition from one 4f to another 4f orbital.
number of unpaired electron ions in Ce3+ and Yb3+ is 1 and no f-f transition for the f1 and f13 as there no 4f upper state so they absorb in the visible region and appear colourless . 
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