Functional assembly of nonlinear optical (NLO) motifs
with a large
optical anisotropy is vital to the development of advanced NLO and
birefringent materials. In this work, we highlight that, in addition
to heteroatomic NLO motifs, homoatomic anionic clusters formed by
aggregated anions (S, Se, Te) exhibit diverse chain-, ring-, and cage-like
chemical structures as well as one-, two-, and three-dimensional motif
alignments. The rich structural chemistry enables homoatomic polychalcogenides
(HAPCs) to exhibit asymmetric structural features and anisotropic
optical properties, with great potential for NLO and birefringent
performance. Focusing on totally 55 binary HAPCs A2Q
n
(n = 2, 3, 4, 5; A = Na, K,
Rb, Cs; Q = S, Se, Te) and their ternary analogues, we employ the
state-of-the-art first-principles approach to systematically investigate
the modulation evolution of their NLO and birefringent properties.
Remarkably, Rb2Te3 and Na2TeSe2 exhibit rarely colossal birefringence (>1.0@10 μm)
and NLO effects (>20 × AgGaS2), much larger than
conventional
NLO chalcogenides. Na2Te3 presents the largest
birefringence to date (∼3.48@1, 2.72@2, 2.34@10 μm),
indicating the unique structural superiority of HAPC in terms of ultra-large
birefringence. By mining the intrinsic mechanism, the HAPC anionic
groups are identified as novel mid-infrared NLO “material genes”,
furnishing unique NLO and birefringent performance for the design
of novel optoelectronic materials.