Abstract: Lithium niobate (LiNbO₃, LN) is an artificial crystal with excellent physical properties, such as acousto-optic, electro-optic, piezoelectric, and photorefractive, etc. It was not only regarded as "optical silicon", but also proposed that human beings are entering the era of "Lithium Niobate Valley". Its excellent optoelectronic properties have a wide prospect of applications in emerging fields, such as artificial intelligence and photoelectric hybrid module. Photorefractive was found and proved to be an important property of lithium niobate crystal. With the development of optoelectronic devices based on lithium niobate to micro- and nano- scale, photorefractive effect has gradually appeared. Single crystal lithium niobate is the basic material for preparing various devices based on lithium niobate on insulator (LNOI). The photorefractive properties can be adjusted by doping appropriate impurity ions. Comparing with normal ions (Valence < +5 valence of niobium ions), it has been found that the incorporation of high-valence ions (Valence ≥ +5 valence of niobium ions) can be more beneficial to improve the photorefractive performances of lithium niobate crystals in recent years. This paper summarizes the research progress of high-valence ion-doped lithium niobate crystals. The generalization and summarization show that doping V, Mo, U, Bi ions can be effective methods to adjust photorefractive properties of lithium niobate, which can be beneficial in micro-ring resonator, optically programmable photonic components, nonlinear photonic device, and other micro- and nano- scale devices based on LN. Meanwhile, it is proposed that further research based on high-valence ions doped lithium niobate can be carried out in four aspects: high-quality and size crystal growth, photorefractive mechanism, other ion doping with lone-pair electrons, and exploration of optoelectronic devices based on them.

Key words: lithium niobate, high valence ions, photorefractive performance, review