Comparative Investigation of Green and Red Upconversion Luminescence in Er3+ Doped and Yb3+/Er3+ Codoped LaOCl

Pure tetragonal LaOCl:Er3+ and LaOCl:Yb3+/Er3+ samples possessing upconversion (UC) luminescence behavior were synthesized using a simple solid-state reaction method and the structural properties were investigated using X-ray diffraction, crystal structure analysis, and SEM, respectively. The UC spectroscopic properties of Er3+ doped and Yb3+/Er3+ codoped LaOCl were studied in terms of UC emission spectra. The intense green and red emissions around 528, 550, and 662 similar to nm corresponding to the 2H11/2?4I15/2, 4S3/2?4I15/2, and 4F9/2?4I15/2 transitions of Er3+ ions were observed for LaOCl:Er3+ sample under excitation at 980 similar to nm, and the power studies indicated that two-photon processes were responsible for the green and red upconversion luminescence. The bright green emission is visible to the naked eyes for LaOCl:Er3+. A great enhancement of the visible upconversion emissions in Yb3+/Er3+-codoped sample was observed, furthermore, it is interesting to find the bright red emission for LaOCl:Yb3+/Er3+ samples. The mechanisms for the green and red UC luminescence, especially the enhancement of red UC emission were discussed based on the law of UC intensity versus pump power and their lifetimes.