Looking Back the Nonlinear Optical Crystals in a Functionalized Unit's Perspective

Abstract Nonlinear optics, signifying a revolutionary paradigm change within the realm of optics, has ushered in a transformative era by employing the nonlinear optical crystals to manipulate and harness the laser power for at least six decades. The most exciting aspects of nonlinear optical (NLO)crystal is the repercussions of bonding over extended functionalized units to external force and how slight alterations at the atomic scale can result in huge changes in the macroscopic properties. However, to date, precisely controlling the functionalized unit and its potential to induce directed property is, yet, not fully realized. Here, the NLO crystals are explored and prospected from the viewpoint of a functionalized unit, with an emphasis on the application of functionalized units in material design to control and regulate key optical properties and start regulating their functions. An introduction of anionic group theory is started here, which considers the functional unit to be primary, then turns to a discussion of functionalized unit modification through emerging design strategies and how this facilitates the design of new NLO materials. Additional breakthroughs in rational design strategy to fully functionalize the groups are covered, including integration, preferential arrangement induction, microcosmic performance maximization for functionalized units as well as the supports of these for new materials discovery with a theoretical method. Beyond the gratifying achievements made, some future perspectives to move NLO crystals a step forward are finally provided.