Phase Matching Achieved by Bandgap Widening in Infrared Nonlinear Optical Materials[ABa_(3)Cl_(2)][Ga_(5)S_(10)](A=K,Rb,and Cs)

Large nonlinear optical(NLO)coefficient(d_(ij)),high laser damage threshold(LDT),and phase matching(PM)are crucial for the practical applications of IR NLO crystals.A great number of IR NLO materials with high dij have been explored,but many of them suffer from non-PM,which dramatically decreases their ultimate NLO output efficiencies.To settle this problem,we have developed a new strategy involving modulating normal dispersion via bandgap(E_(g))widening to achieve PM in this work.We synthesized successfully three new wide E_(g)(∼4.0 eV)IR NLO salt-inclusion sulfides[ABa_(3)Cl_(2)][Ga_(5)S_(10)](A=K,1;Rb,2;and Cs,3)with PM behaviors,mainly ascribed to the PM cut-off wavelength blue shift that originated from the wide Eg values,with less contribution from birefringence enhancement.All the compounds possessed large second-harmonic-generation(SHG)efficiency(∼1×AgGaS_(2))and hitherto the highest LDTs(188–200 MW/cm^(2),at 1.06μm,10 ns pulse width)for known chalcogenides with SHG efficiencies comparable to that of commercial silver gallium sulfide(AgGaS_(2))crystal.