Two Metal Phosphate Nonlinear Optical Materials Simultaneously Exhibiting Ultraviolet Transparence and a Large Birefringence

Abstract

For phosphate nonlinear optical (NLO) materials, how to improve their small birefringence is confronted with a great contradiction of their weak optical anisotropy of tetrahedral PO4 groups. Herein, by introducing La3+ with a closed-shell structure and Cd2+ with a d10 electronic configuration, two NLO materials with a large birefringence, namely, La­(PO3)3 (0.040@1064 nm) and β-Cd­(PO3)2 (0.059@1064 nm), have been synthesized by a high-temperature solution method. In particular, for β-Cd­(PO3)2, it possesses the largest birefringence among the known deep-ultraviolet (DUV) phosphates to date, which is attributed to cooperative effects of strong covalence of Cd–O groups and P–O pseudolayers similar to those of a plane. Meanwhile, β-Cd­(PO3)2 exhibits the shortest cutoff edge (<190 nm) among the reported Cd-based inorganic compounds and realizes a balance between DUV transparence and a large birefringence. This insight provides a new opportunity to design high-performance NLO materials using metal phosphates.

Structure and optical property evolution in PbM(PO4)X (M = Zn, Sn; X = halogen): SHG effect and birefringence

“…[13][14][15][16] Currently, metal phosphates are an important source for NLO material applications due to their structural advantages and good physicochemical properties, with familiar KTiOPO 4 (KTP) and KH 2 PO 4 (KDP) being reported and successfully commercialized in the 1970s. In recent years, a series of novel metal phosphates were successfully explored as promising NLO materials, such as LiPbPO 4 (about 3 × KDP, 0.021@1064 nm), 17 Cs 2 LiPO 4 (1.8 × KDP), 18 LiHgPO 4 (11 × KDP, 0.068@1064 nm), 19 KMg(H 2 O)PO 4 (about 1.14 × KDP, 0.017@1064 nm), 20 Rb 3 PbBi(P 2 O 7 ) 2 (2.5 × KDP, 0.025@1064 nm), 21 Bi 32 Cd 3 P 10 O 76 (about 4 × KDP), 22 β-Cd(PO 3 ) 2 (0.25 × KDP, 0.059@1064 nm), 23 Na 3 Sc 2 (PO 4 ) 2 F 3 (0.26 × KDP, 0.0978@546.1 nm), 24 CsMgPO 4 •6H 2 O (1.36 × KDP, 0.0060@1064 nm), 25 K 4 Mg 4 (P 2 O 7 ) 3 (1.3 × KDP, 0.0108@1064 nm), 26 and K 2 Sb(P 2 O 7 )F (4.0 × KDP, 0.157@546 nm). 27 However, the microscopic second-order multiplicity coefficients of the PO 4 group, the basic structural unit of phosphates, is much smaller than that of the BO 3 group, and the rigid PO 4 group also exhibits weak anisotropy, which greatly hampers the availability of phosphates in the field of NLO materials.…”

Cd(NH2SO3)2·xH2O (x= 0, 2): new sulfamates with a unique coordination environment and reversible phase transitions

“…, phosphates, borophosphates, sulfates and silicates, are also important and well-developed owing to their large HOMO–LOMO gaps and wide transparency windows. Many crystals found in these systems, including but not limited to La(PO 3 ) 3 , 37 Ba 5 P 6 O 20 , 38 Ba 3 (ZnB 5 O 10 )PO 4 , 39 A 2 BeS 2 O 8 (A = NH 4 , K, Rb, Cs) 40 and Cs 2 B 4 SiO 9 , 41 also exhibit outstanding SHG performances. Furthermore, polar anionic tetrahedra with enhanced anisotropy such as [BO 3 F], [PO 3 F] and [SO 3 F] were employed to form advanced deep-UV NLO materials such as CsB 4 O 6 F, 42 SrB 5 O 7 F 3 , 43 (NH 4 ) 2 PO 3 F 44 and C(NH 2 ) 3 SO 3 F. 45 In recent years, several sulfamates have been considered, including Sr(NH 2 SO 3 ) 2 , 46 Ba(NH 2 SO 3 ) 2 and KNO 3 SO 3 NH 3 , 47 which exhibit promising NLO properties.…”

“…On the other hand, NLO materials composed of tetrahedral anionic groups, i.e., phosphates, borophosphates, sulfates and silicates, are also important and well-developed owing to their large HOMO-LOMO gaps and wide transparency windows. Many crystals found in these systems, including but not limited to La(PO 3 ) 3 , 37 45 In recent years, several sulfamates have been considered, including Sr(NH 2 SO 3 ) 2 , 46 Ba(NH 2 SO 3 ) 2 and KNO 3 SO 3 NH 3 , 47 which exhibit promising NLO properties. In addition, a new non-π-conjugated tetrahedral [NH 2 SO 3 ] has been proposed as a promising functional unit for designing novel NLO materials.…”

Controlling the Nonlinear Optical Behavior and Structural Transformation with A‐Site Cation in α‐AZnPO4 (A = Li, K)

“…For phosphate NLO crystals, [PO 4 ] 3− and [PO 4‐x F x ] (x−3)‐ ( x = 1, 2) have been proved to be promising entities with wide band gaps ( E g ) and small chromatic dispersion, which means more moderate demands for birefringence. [ 10 ] So far, some phosphates and fluorophosphates, involving MNaMgP 2 O 7 (M = Rb, Cs), [ 11 ] LiCs 2 PO 4 , [ 12 ] LiHgPO 4 , [ 13 ] Ba 2 NaClP 2 O 7 , [ 14 ] M 4 Mg 4 (P 2 O 7 ) 3 (M = K, Rb), [ 15 ] A 3 BBi(P 2 O 7 ) 2 (A = Rb, Cs; B = Pb, Ba), [ 16 ] β‐CdP 2 O 6 , [ 17 ] (NH 4 ) 2 PO 3 F, [ 18 ] NaNH 4 PO 3 F·H 2 O, [ 19 ] K 2 Sb(P 2 O 7 )F, [ 20 ] were reported with promising NLO properties. However, how to obtain phosphates with large second harmonic generation (SHG) and short cut‐off edge is always a hot topic.…”