An experimental technique using powders is described which permits the rapid classification of materials according to(a) magnitude of nonlinear optical coefficients relative to a crystalline quartz standard and(b) existence or absence of phase matching direction(s) for second‐harmonic generation.Results are presented for a large number of inorganic and organic substances including single‐crystal data on phase‐matched second‐harmonic generation in HIO3, KNbO3, PbTiO3, LiClO4·3H2O, and CO(NH2)2. Iodic acid (HIO3) has a nonlinear coefficient d14∼1.5×d31 LiNbO3. Since it is readily grown from water solution and does not exhibit optical damage effects, this material should be useful for nonlinear device applications.

A Powder Technique for the Evaluation of Nonlinear Optical Materials

Publisher Summary A number of recent crystal structure determinations on compounds of the nonmetals have discovered intramolecular distances that are much longer than normal bonds, and intermolecular distances that are much shorter than van der Waals distances. In this chapter, these interactions are examined and a qualitative explanation is attempted. It will become clear that in most of them an approximately linear arrangement is found, Y-A—X where Y-A is a normal bond and A—X is a short intermolecular distance. It is with these approximately linear interactions that we are particularly concerned, and it will be our contention that they are the result of directed forces and that their behavior is sufficiently regular and understandable for the name secondary bond to be appropriate. The only conclusive method of establishing the presence of secondary interactions is by crystal structure determinations. An intermolecular interaction can be recognized as being significant by being shorter than the expected intermolecular (van der Waals) distance, but if it is the result of directed forces— that is, bonds rather than electrostatic or nondirectional van der Waals forces.

Secondary Bonding to Nonmetallic Elements

By combination of Nb5+ (having a d0 electronic configuration) and the lone-pair-containing iodate anion, a new SHG material, BaNbO(IO3)5, has been prepared. It exhibits a very large SHG response (∼14 times that of KH2PO4 and ∼660 times that of α-SiO2) and is phase-matchable. The material has high thermal stability and a wide transparent region.

BaNbO(IO3)5: a new polar material with a very large SHG response.

Clear, transparent (0.5–5.0 μ), solution‐grown, single crystals of negative uniaxial LiIO3 show no optically induced damage and remain stable in the temperature range 20°–256°C. The crystals are of point group 6 and are optically active and pyroelectric. We have measured the linear electrooptic coefficients in the visible and the optical activity in the infrared. For λ1=1.0845 μ phase‐matched second harmonic generation (PMSHG) occurred at θm=28.9° and this angle changed by less than 0.3° in the range 20–256°C. PMSHG was employed to determine the single domain quality of the crystals and to measure | d31(LiIO3)/d36(KDP) |=11. At 1.06 μ we have measured the coherence lengths and the ratio of the nonlinear coefficients | d33/d31 |=0.8.

Optical Nonlinearities in LiIO3

2-amino-5-nitropyridinium dihydrogen monophosphate exemplifies a new crystal engineering strategy combining mineral and organic moieties towards enhanced quadratic nonlinear optical properties. This strategy is meant to combine the advantages of mineral ionic structures (cohesion, stability, optical and other damage resistance) with those of organic molecules (structural flexibility, high optical polarizability). This organic inorganic material is designed so as to favour mutual dipolar interactions between the 2-amino-5-nitropyridinium cations and the (H2PO4−)n subnetwork interlocked by hydrogen bonding in the same crystalline lattice. This approach rests on the structural features and chemical properties of (H2PO4−)n polyanion. The 2A5NPDP structure reveals a polar layered arrangement. The high powder SHG efficiency of 2A5NPDP, comparable to that of state-of-the-art purely organic 3-methyl-4-nitropyridine-1-oxide (POM) crystals, confirms the validity of this approach, currently generalized to a large variety of mixed organo-mineral crystals.

A new approach in the design of polar crystals for quadratic nonlinear optics exemplified by the synthesis and crystal structure of 2-amino-5-nitropyridinium dihydrogen monophosphate (2A5NPDP)

http://journals.iucr.org/q/issues/1966/06/00/a05127/a05127.pdf

B. Morosin

Papers

A reinvestigation of the crystal structure of LiIO3