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.