Manipulating the singular red emission in GdOF:Yb/Er nanosheets via defect engineering

Efficient tailoring of red emission in a selectively emitting Yb3+/Er3+ up-conversion (UC) system is of great significance for optical applications. In this study, we adopted a facile and effective method to obtain a pure red emission by defect engineering in GdOF:Yb3+/Er3+ (6/x mol%) nanosheets. It was observed that the defect engineering was realized by NaF etching of the precursors in a low-temperature water bath reaction. As a result, the probability of multi-phonon relaxation processes was increased, resulting in a red to green (R/G) ratio higher than 19 for all samples. The products perfectly inherited the sheet-like morphology of the precursors. Furthermore, the effect of calcination temperature on the UC emission selectivity was demonstrated in GdOF:Yb3+/Er3+ nanocrystals. The R/G ratio of the samples obtained at 500 °C was increased by about 3–4 times compared with the samples obtained at different calcination temperatures. By combining the results with the outcomes of spectroscopic analyses, we simulated the role of defects in improving the R/G ratio of GdOF:Yb3+/Er3+ samples using a model. The exciting discovery of the ability of defect engineering to modulate UC emission selectivity not only provides a general method to tailor red emission in a Yb3+/Er3+ UC system, but also facilitates multicolor displays, anti-counterfeiting, and tissue bioimaging.