Yan Zhan, Ting Geng, Yingliang Liu, Chaofan Hu, Xuejie Zhang, Bingfu Lei, Jianle Zhuang, Xu Wu,* Di Huang,* Guanjun Xiao,* and Bo Zou, “Near-ultraviolet to near-infrared fluorescent nitrogen-doped carbon dots with two-photon and piezochromic luminescence”