Due to the quantum size effect and other unique photoelectric properties,quantum dots (QDs) have attracted tremendous interest in nanoscience,leading a lot of milestone works.Meantime,the scope and scientific connotation of QDs are constantly expanding,which demonstrated amazing development vitality.Besides the well-developed Cd-containing Ⅱ-Ⅵ semiconductors,QDs of environmentally friendly Ⅰ-Ⅲ-Ⅵ (Ⅰ =Cu,Ag;Ⅲ =Ga,In;Ⅵ =S,Se) chalcogenides have been a hot spot in the QDs family,which are different from traditional Ⅱ-Ⅵ QDs in terms of multi-composition,complex defect structure,synthetic chemistry and optical properties,bringing a series of new laws,new phenomena and new challenges.The composition of Ⅰ-Ⅲ-Ⅵ chalcogenides and their solid solutions can be adjusted within a very large range while the anion framework remains stable,giving them excellent capability of photoelectric property manipulation.The important features of Ⅰ-Ⅲ-Ⅵ QDs include wide-range bandgap tuning,large Stokes shift and long photoluminescence (PL) lifetime,which are crucial for biological,optoelectronic and energy applications.This is due to the coexistence of two or more metal cations leading to a large number of intrinsic defects within the crystal lattice also known as deep-donor-acceptor states,besides the commonly observed surface defects in all QDs.However,a profound understanding of their structure and optoelectronic properties remains a huge challenge with many key issues unclear.On one hand,the achievements and experience of traditional QD research are expected to provide vital value for further development of Ⅰ-Ⅲ-Ⅵ QDs.On the other hand,the understanding of the emerging new QDs,such as carbon and other 2D materials,are even more challenging because of the dramatically different composition and structure from Ⅱ-Ⅵ semiconductors.For this,Ⅰ-Ⅲ-Ⅵ QDs,as a close relative to Ⅱ-Ⅵ QDs but with much more complex composition and structure variation,provide a great opportunity as a gradual bridge to make up the big gap between traditional QDs and emerging new QDs,such as carbon dots.Here,we hope to compare the research progress of Ⅰ-Ⅲ-Ⅵ QDs and Ⅱ-Ⅵ QDs,in an effort to comprehensively understand their structure,synthetic chemistry,optical electronic and photocatalytic properties.We further give insights on the key potential issues of Ⅰ-Ⅲ-Ⅵ QDs from the perspective of bridging between traditional QDs and emerging carbon dots,especially the profound principles behind synthetic chemistry,PL mechanism and optoelectronic applications.