posted on 2021-06-23, 16:37authored byYilei Hu, Xingxing Jiang, Chao Wu, Zhipeng Huang, Zheshuai Lin, Mark G. Humphrey, Chi Zhang
Tailored structural modulation to
combine a broad optical band
gap, large nonlinear optical (NLO) effect, and moderate birefringence
in a single molecule is a crucial challenge for functional NLO material
design. In this study, two first fluorinated molybdate fluoroiodates A2MoO2F3(IO2F2) [A = Rb (RMOFI), Cs (CMOFI)] were
successfully accomplished by combining fluorinated d0-transition
metal (TM) octahedra [MoO3F3] with fluoroiodate
group [IO2F2]. These two compounds crystallize
in noncentrosymmetric space group Cmc21 while featuring a zero-dimensional (0D) [MoO2F3(IO2F2)]2– functional motif,
and their respective alkali–metal cations act as linkers in
polyanions. Both RMOFI and CMOFI possess large second-harmonic generation
(SHG) effects (5.0 × KH2PO4 (RMOFI) and
4.5 × KH2PO4 (CMOFI) at 1064 nm), wide
band gaps (3.77 eV (RMOFI) and 3.43 eV (CMOFI)), sufficient birefringences
(0.217 (RMOFI) and 0.204 (CMOFI) at 1064 nm) to achieve phase-matchable
(PM) and broad infrared (IR) transparency region, suggesting that
RMOFI and CMOFI can be promising NLO materials in the IR field. Theoretical
calculations elucidate that the strong SHG responses and enlarged
birefringences of the title compounds originate from the 0D [MoO2F3(IO2F2)]2– functional unit. This is in sharp contrast to the previous work
that most fluoroiodates adopt centrosymmetric structures. Our study
illustrates that introducing fluorinated d0-TM octahedra
into fluoroiodate systems can be a facile method for developing high-performance
nonlinear optical materials.