Two Mixed-Alkali-Metal Selenates as Short-Wave Ultraviolet Nonlinear-Optical Materials

Abstract

Two novel mixed-alkali-metal selenate nonlinear-optical (NLO) crystals, Na 3 Li(H 2 O) 3 (SeO 4 ) 2 •3H 2 O (I) and CsLi 3 (H 2 O)(SeO 4 ) 2 (II), have been successfully synthesized by an aqueous solution evaporation method. Both compounds feature the unique layers constructed of the same functional moieties including SeO 4 and LiO 4− layers in II. The titled compounds display wide optical band gaps of 5.62 and 5.66 eV, respectively, according to the UV−vis spectra. Interestingly, they exhibit significantly different second-order nonlinear coefficients (0.34 × KDP and 0.70 × KDP, respectively). Detailed dipole moment calculations manifest that the large disparity can be attributed to the difference in the dipole moment of the crystallographically independent SeO 4 and LiO 4 groups. This work confirms that alkalimetal selenate system is an excellent candidate for short-wave ultraviolet NLO materials.

Na7(SeO4)3(IO3) and K2(SeO4)[IO2(OH)]: two new iodate-selenates with short-wave UV cutoff edge and large birefringence

“…Due to the introduction of highly polarizable polyhedra ([IO 3 ]/[IO 2 (OH)]), the birefringence values are significantly greater than those of some reported alkali/alkaline earth metal crystals containing only tetrahedral anion groups, e.g. , Na 3 Li(H 2 O) 3 (SeO 4 ) 2 ·3H 2 O (0.001@546 nm), 25 NH 4 NaLi 2 (SO 4 ) 2 (0.008@1064 nm), 20 LiCs 2 PO 4 (0.008@1064 nm), 24 K 4 Mg 4 (P 2 O 7 ) 3 (0.0108@1064 nm), 23 CsLi 3 (H 2 O)(SeO 4 ) 2 (0.02@546 nm), 25 Li 8 NaRb 3 (SO 4 ) 6 ·2H 2 O (0.021@1064 nm), 21 and NaNH 4 PO 3 F·H 2 O (0.053@589 nm). 60…”

“…Thus, the birefringence was calculated as 0.087 and 0.101 at 546 nm, respectively. Due to the introduction of highly polarizable polyhedra ([IO 3 ]/[IO 2 (OH)]), the birefringence values are significantly greater than those of some reported alkali/alkaline earth metal crystals containing only tetrahedral anion groups, e.g., Na 3 Li(H 2 O) 3 (SeO 4 ) 2 Á3H 2 O (0.001@546 nm), 25 NH 4 NaLi 2 (SO 4 ) 2 (0.008@1064 nm), 20 LiCs 2 PO 4 (0.008@1064 nm), 24 K 4 Mg 4 (P 2 O 7 ) 3 (0.0108@1064 nm), 23 CsLi 3 (H 2 O)(SeO 4 ) 2 (0.02@546 nm), 25 Li 8 NaRb 3 (SO 4 ) 6 Á2H 2 O (0.021@1064 nm), 21 and NaNH 4 PO 3 FÁH 2 O (0.053@589 nm). 60 In order to investigate the origin of the large birefringence ulteriorly, we calculated the cosy values of the angle between the optical principal axis (n min ) and the orientation of the lone pair of electrons (K i ).…”

“…24 Now, the selenate optical crystals are also gradually being studied, as the 4s and 4p orbitals of the Se atom in the [SeO 4 ] tetrahedral group are more diffuse than the 3s and 3p orbitals of the S atom, leading to a more deformable electron cloud. However, relying solely on the [SeO 4 ] tetrahedral group, the birefringence and the SHG effect cannot be perfected while ensuring a short cutoff edge, e.g., CsLi 3 (H 2 O)(SeO 4 ) 2 (219 nm, 0.020@546 nm, 0.7 Â KDP), 25 Na 3 Li-(H 2 O) 3 (SeO 4 ) 2 Á3H 2 O (221 nm, 0.001@546 nm, 0.34 Â KDP), 25 and Na 5 (SeO 4 )(HSeO 4 ) 3 (H 2 O) 2 (347 nm, 0.037@1064 nm, 1.6 Â KDP). 26 So it is urgent to have a suitable strategy to improve the overall optical performance of selenate crystals.…”

“…However, relying solely on the [SeO 4 ] tetrahedral group, the birefringence and the SHG effect cannot be perfected while ensuring a short cutoff edge, e.g. , CsLi 3 (H 2 O)(SeO 4 ) 2 (219 nm, 0.020@546 nm, 0.7 × KDP), 25 Na 3 Li(H 2 O) 3 (SeO 4 ) 2 ·3H 2 O (221 nm, 0.001@546 nm, 0.34 × KDP), 25 and Na 5 (SeO 4 )(HSeO 4 ) 3 (H 2 O) 2 (347 nm, 0.037@1064 nm, 1.6 × KDP). 26 So it is urgent to have a suitable strategy to improve the overall optical performance of selenate crystals.…”

SrCl2·6H2O: An Alkaline-Earth-Metal Chloride Hexahydrate as Deep-Ultraviolet Nonlinear-Optical Crystal with the {[Sr(H2O)6]2+}∞ Cationic Framework

“…The peaks at 3356, 1656, and 1630 cm –1 indicate the presence of H 2 O molecules, which contain the stretching and vibration of O–H bonds. The peaks of 710–546 cm –1 show the bend vibration of Sr–O bonds. , …”