Environmental and energy issues are the two main challenges that hinder the sustainable development of human society. [1][2][3][4][5][6] Solar energy has attracted urgent attention due to

It is still challenging to design a stable and efficient catalyst for visible‐light CO2 reduction. Here, Er3+ single atom composite photocatalysts are successfully constructed based on both the special role of Er3+ and the special advantages of Zn2GeO4/g‐C3N4 heterojunction in the photocatalysis reduction of CO2. Especially, Zn2GeO4:Er3+/g‐C3N4 obtained by in situ synthesis is not only more conducive to the tight junction of Zn2GeO4 and g‐C3N4, but also more favorable for g‐C3N4 to anchor rare‐earth atoms. Under visible‐light irradiation, Zn2GeO4:Er3+/g‐C3N4 shows more than five times enhancement in the catalytic efficiency compared to that of pure g‐C3N4 without any sacrificial agent in the photocatalytic reaction system. A series of theoretical and experimental results show that the charge density around Er, Ge, Zn, and O increases compared with Zn2GeO4:Er3+, while the charge density around C decreases compared with g‐C3N4. These results show that an efficient way of electron transfer is provided to promote charge separation, and the dual functions of CO2 molecular activation of Er3+ single atom and 4f levels as electron transport bridge are fully exploited. The pattern of combining single‐atom catalysis and heterojunction opens up new methods for enhancing photocatalytic activity.