Abstract
Two nonlinear optical crystals, BaVO(IO3)5 and BaTaO(IO3)5, are designed by substituting Nb with V and Ta, respectively, in BaNbO(IO3)5, which is itself a recently synthesized infrared nonlinear optical (NLO) material. The designs of BaVO(IO3)5 and BaTaO(IO3)5 from BaNbO(IO3)5 are based on the following motivation: BaVO(IO3)5 should have a larger second-harmonic generation (SHG) coefficient than BaNbO(IO3)5, as V will result in a stronger second-order Jahn-Teller effect than Nb due to its smaller ion radius; at the same time, BaTaO(IO3)5 should have a larger laser-damage threshold, due to the fact that Ta has a smaller electronegativity leading to a greater band-gap. Established on reliable first-principle calculations, it is demonstrated that BaVO(IO3)5 has a much larger SHG coefficient than BaNbO(IO3)5 (23.42 × 10−9 vs. 18.66 × 10−9 esu); and BaTaO(IO3)5 has a significantly greater band-gap than BaNbO(IO3)5 (4.20 vs. 3.55 eV). Meanwhile, the absorption spectra and birefringences of both BaVO(IO3)5 and BaTaO(IO3)5 are acceptable for practice, suggesting that these two crystals can both be expected to be excellent infrared NLO materials.
Highlights
Great effort has been made in searching for new second-order nonlinear optical (NLO) materials for their increasingly important role in many advanced scientific and technological areas, especially in laser technology [1,2,3,4,5,6,7]
As the NLO crystals used in the infrared region are inadequate for applications at present [13,14,15], BaNbO(IO3 )5 has been widely studied [16,17] since it was first synthesized
BaMO(IO3 )5 unit is illustrated in Figure 1, in which the anionic group MO(IO3 )5 2− shows a typical “zero-dimensional” structure: the M atom is in the center of a MO6 octahedron, and it links to five oxygen atoms in iodate groups and one terminal oxygen atom. This anionic group plays the main role in the second-order Jahn-Teller (SOJT) effect the second-harmonic generation (SHG) response [18], and in affecting Eg of the crystal, while the
Summary
Great effort has been made in searching for new second-order nonlinear optical (NLO) materials for their increasingly important role in many advanced scientific and technological areas, especially in laser technology [1,2,3,4,5,6,7]. Metal iodates attract a lot of attention as several them have shown large second-harmonic generation (SHG) coefficients, high laser-damage thresholds (LDT), wide transparent wavelength regions, and good thermal stability [8,9,10,11]. Materials 2018, 11, 1809 the general criteria for the scientific research and industrial application of a NLO crystal are that the SHG coefficient should be 10 times larger than that of KDP (1.1 × 10−9 esu) [9], and Eg should be greater than 3.0 eV. As the NLO crystals used in the infrared region are inadequate for applications at present [13,14,15], BaNbO(IO3 ) has been widely studied [16,17] since it was first synthesized
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