Heteroanionic LaBrVIO₄ (VI = Mo, W): Excellence in Both Nonlinear Optical Properties and Photoluminescent Properties

Abstract

Five heteroanionic oxybromides, LaBrMoO4, LaBrWO4, (La0.9Sm0.1)BrMoO4, (La0.9Sm0.1)BrWO4, and (La0.9Dy0.1)BrWO4, were grown by a high-temperature salt flux method. Millimeter-sized crystals were collected after salt flux was removed by DI water. The crystal structures were accurately determined by single-crystal X-ray diffraction. LaBrMoO4 is isostructural to LaBrWO4. The substitution of lanthanum for rare earth elements does not change the crystal structure. LaBrWO4 is the first acentric tungsten-containing compound of the REBrVIO4 (RE = Y, La–Lu; VI = Mo, W) system. The bonding picture of LaBrWO4 was understood by crystal orbital Hamilton population calculations (COHP) and electron localization function (ELF) analysis, which confirmed the uncommon 4 + 1 coordination of tungsten surrounded by oxygen atoms. Linear optical properties such as bandgaps, infrared spectrum (IR), and birefringence of the title compounds were recorded in this work. LaBrMoO4 exhibits a moderate second harmonic generation (SHG) response of 0.47× KH2PO4 (KDP) for incident 1064 nm radiation. LaBrWO4 and (La0.9Dy0.1)BrWO4 exhibit superior SHG responses of 1.66× KDP and 3.71× KDP for samples for incident 1064 nm radiation, respectively. All measured samples exhibited type-I phase matching behavior. Density function calculations (DFT) verified that the optical properties of LaBrMoO4 and LaBrWO4 are predominantly controlled by [VIO5]VI = Mo,W units. Via the rare earth elements Sm and Dy doping, LaBrMoO4 and LaBrWO4 emit visible lights of various wavelengths upon UV light excitation. The distortion of lambda-shaped one-dimensional (1D) [VIO5]VI = Mo,W strands plays an important role in enhancing nonlinear optical properties and photoluminescent properties within LaBrWO4 and (La0.9Dy0.1)BrWO4 compared with LaBrMoO4.

Synthesis, crystal and electronic structures, linear and nonlinear optical properties, and photocurrent response of oxyhalides CeHaVIO4 (Ha = Cl, Br; VI = Mo, W)

“…60 CeBrWO 4 is a new compound, which has never been reported. Like CeBrMoO 4 and CeClMoO 4 , CeBrWO 4 is also isotypic to LaBrWO 4 32 and crystallizes in the acentric monoclinic space group Pc (no. 7) with unit cell parameters of a = 9.8783(1) Å, b = 5.9223(1) Å, c = 7.9394(1) Å, and β = 90.008(1)°.…”

“…Our previous bonding picture study of LaBrWO 4 revealed the moderately strong interaction of the elongated W–O interactions of 2.24 Å. 32 The 2D [CeBrO 4 ] 6− strips are built by distorted tetracapped trigonal prisms [CeO 6 Br 3 ], where six oxygen atoms and three bromine atoms surround the central Ce atoms. The Ce–Br interactions fall into the range of 3.1393(16)–3.257(2) Å, which is similar to many compounds that include Ce–Br interactions such as, CeBr 3 (3.108–3.158 Å), 66 CeBrMoO 4 (3.112–3.227 Å), 60 Ce 3 (SiS 4 ) 2 Br (3.101–3.328 Å), 67 etc .…”

“…Oxyhalides, which constitute two anions of oxygen and halogen, have been emerging as important NLO materials, especially for covering the visible or ultraviolet spectrum range, but have been rarely used for IR NLO applications. 32–42 There are two major reasons for this: first, the presence of metal–oxygen bonds, whose intrinsic vibrations are over the spectrum ranges of 3–5 μm and 8–12 μm, resulting in high optical absorption of the desired IR spectrum range; second, the strong ionic metal–halogen interactions, which have tight bonding of valence electrons around anions, generating very large bandgaps. 32–42 A very large bandgap is usually accompanied by a small SHG response.…”

“…32–42 There are two major reasons for this: first, the presence of metal–oxygen bonds, whose intrinsic vibrations are over the spectrum ranges of 3–5 μm and 8–12 μm, resulting in high optical absorption of the desired IR spectrum range; second, the strong ionic metal–halogen interactions, which have tight bonding of valence electrons around anions, generating very large bandgaps. 32–42 A very large bandgap is usually accompanied by a small SHG response. Hence, a good strategy to “push” oxyhalides into the IR spectrum range is necessary.…”

Visualizing the alignment of lone pair electrons in La3AsS5Br2 and La5As2S9Cl3 to form an acentric or centrosymmetric structure

“…Compared with centrosymmetric solids, acentric solids draw growing attention from the research community due to the chance of studying directional physical properties such as second harmonic generation, 1–15 nonreciprocal responses, 16–21 etc. From a chemistry perspective, various strategies have proved efficient to influence the creation of a noncentrosymmetric (NCS) structure, including incorporating second order Jahn–Teller distortion 22,23 and conjugated structure motifs such as distorted FeS 4 14,24 or GeS 4 tetrahedra, 25,26 WO 5 , 27 LaO 6 Br 3 , 28 etc. Another systematic way to influence a NCS structure is through incorporating atoms with stereochemically active lone pairs (SCALPs), including Tl + , Sn 2+ , Pb 2+ , As 3+ , Sb 3+ , Bi 3+ , Te 4+ , etc.…”