Figure 4.

Upconverted emission and absorption spectra of the upconverter in PMMA layer. The emission spectrum is obtained when the upconverter shows no saturation and only emission peaks from the 4S3/2, 2H11/2 (510 to 560 nm), and 4F9/2 (650 to 680 nm) states are observed.

van Sark et al. Nanoscale Research Letters 2013 8:81   doi:10.1186/1556-276X-8-81
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