From what I have been studying so far,
Burn down charts : tells you remaining work to complete , it is hard to measure team productivity because more work can be added (remember Agile encourages changes, so more work can be added)
Burn up charts: can measure development team productivity, number of story points they completed in "each" of the past iterations
I would note that the appropriate Information Radiator to measure Agile Team productivity is use of "Burn Up Charts". Remember Agile Manifesto #7 : Working Software is the primary measure of progress.