Uniform upconversion film with large area prepared by improved confined-space synthesis method

We prepared uniform and large-scaled upconversion films with the greatly enhanced fluorescence using a modified confined-space synthesis method. The diffusion of NaYF₄:20%Yb, 0.5%Tm precursors into the confined-space that was constructed by three overlapping silica glass substrates was facilitated by designing open channels into the upper substrate. A uniform upconversion film with an area of 4 cm × 4 cm was prepared, which can transfer the near-infrared light of 980 nm into 346, 361, 452, 475, 646, and 802 nm. In comparison with the film prepared without open channels, the fluorescence intensity of the upconversion film here was increased by 20 times.