Heteroanionic $LaBrVIO_{4}$ (VI = Mo, W): Excellence in Both Nonlinear Optical Properties and Photoluminescent Properties

Abstract

Five heteroanionic oxybromides, $LaBrMoO_{4}$, $LaBrWO_{4}$, $(La_{0.9}Sm_{0.1})BrMoO_{4}$, $(La_{0.9}Sm_{0.1})BrWO_{4}$, and $(La_{0.9}Dy_{0.1})BrWO_{4}$, 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. $LaBrMoO_{4}$ is isostructural to $LaBrWO_{4}$. The substitution of lanthanum for rare earth elements does not change the crystal structure. $LaBrWO_{4}$ is the first acentric tungsten-containing compound of the $REBrVIO_{4}$ (RE = Y, La–Lu; VI = Mo, W) system. The bonding picture of $LaBrWO_{4}$ 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. $LaBrMoO_{4}$ exhibits a moderate second harmonic generation (SHG) response of 0.47× $KH_{2}PO_{4}$ (KDP) for incident 1064 nm radiation. $LaBrWO_{4}$ and $(La_{0.9}Dy_{0.1})BrWO_{4}$ 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 $LaBrMoO_{4}$ and $LaBrWO_{4}$ are predominantly controlled by $[VIO_{5}]_{VI} = _{Mo,W}$ units. Via the rare earth elements Sm and Dy doping, $LaBrMoO_{4}$ and $LaBrWO_{4}$ emit visible lights of various wavelengths upon UV light excitation. The distortion of lambda-shaped one-dimensional (1D) $[VIO_{5}]_{VI} = _{Mo,W}$ strands plays an important role in enhancing nonlinear optical properties and photoluminescent properties within $LaBrWO_{4}$ and $(La_{0.9}Dy_{0.1})BrWO_{4}$ compared with $LaBrMoO_{4}$.