  A low temperature hydrothermal route has been developed, and pure phase
Ba$_2$Ni$_3$F$_{10}$ nanowires have been successfully prepared under the
optimized conditions. Under the 325 nm excitation, the Ba$_2$Ni$_3$F$_{10}$
nanowires exhibit three emission bands with peak positions locating at 360 nm,
530 nm, and 700 nm, respectively. Combined with the first-principles
calculations, the photoluminescence property can be explained by the electron
transitions between the t2g and eg orbitals. Clear hysteresis loops observed
below the temperature of 60 K demonstrates the weak ferromagnetism in
Ba$_2$Ni$_3$F$_{10}$ nanowires, which has been attributed to the surface strain
of nanowires. Exchange bias with blocking temperature of 55 K has been
observed, which originates from the magnetization pinning under the cooling
field due to antiferromagnetic core/weak ferromagnetic shell structure of
Ba2Ni3F10 nanowires.

Materials Science;Mesoscale and Nanoscale Physics