Figure 3.

Colloidal solutions of NaYF4:20% Yb3+, 2% Er3+ sample in n-hexane. (A) The solution showing its transparency. (B) Visible upconversion luminescence excited by 980 nm laser oxide. (C) Upconversion luminescence emission spectrum.

Shan et al. Nanoscale Research Letters 2011 6:539   doi:10.1186/1556-276X-6-539
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