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Shang, Xiaoying; Chen, Ping; Jia, Tianqing; Feng, Donghai; Zhang, Shian; Sun, Zhenrong; Qiu, Jianrong . (2015). Upconversion luminescence mechanisms of Er <sup>3+</sup> ions under excitation of an 800 nm laser. Phys. Chem. Chem. Phys., 17(17), 11481–11489. doi:10.1039/C5CP00057B 
An interview with Sci-Hub Founder Alexandra Elbakyan,Who exactly should pay for academic research