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QQ4.03 - A New Mechanism for Energy Transfer Upconversion in NaYF4: Yb3+,Er3+ 
April 23, 2014   9:15am - 9:30am

We propose that the production of blue and red upconversion luminescence in the popular NaYF4: Yb3+,Er3+ nanophosphor occurs via a very different mechanism than that which is commonly accepted. We find that both blue and red are produced through energy transfer upconversion from Yb3+ to Er3+ wherein the Er3+ is promoted from 2H11/2, 4S3/2 up to the high-lying 2K,4G manifold of states, which then rapidly populates the blue emitting state (through multiphonon relaxation) and the red emitting state (through back energy transfer). This new mechanism also impacts the green upconversion luminescence because it removes population from the 2H11/2, 4S3/2 green emitting states. Rate equations simulations based on this model give a quantitative match to experimentally measured luminescence decay curves, relative emission intensities, power dependences, and quantum efficiencies. The model also accurately reflects the optical changes which occur in going from the bulk phosphor to nanomaterials.

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Keynote Address
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