Figure 6.

The photograph of green UCL emissions. (a,b,c) the photograph of 80 μg/mL colloidal solution of as-prepared ILs-UCNP, Cit-UCNP, and SDS-UCNP samples dispersed in ethanol in dark field, the insert in (a) displays solution in bright field (d,e,f,g,h) the photograph of the five kinds of UCNPs powder in bright field (Under the excitation of 980-nm laser diode with power density of 4 W/cm2).

Zhou et al. Nanoscale Research Letters 2013 8:518   doi:10.1186/1556-276X-8-518
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