Effect of Zr4+ concentration on optical properties and defect structure of Zr:Ho:LiNbO3 crystals Li Dai, Shuo Shi, Zhipeng Huang and Xianbiao Li Eur. Phys. J. D, 78 4 (2024) 35 Published online: 02 April 2024 DOI: 10.1140/epjd/s10053-024-00819-5