  We report the colloidal synthesis of strongly fluorescent CsPbBr3 perovskite
nanowires (NWs) with rectangular section and with tuneable width, from 20 nm
(exhibiting no quantum confinement, hence emitting in the green) down to around
3 nm (in the strong quan-tum-confinement regime, emitting in the blue), by
introducing in the synthesis a short acid (octanoic acid or hexanoic acid)
together with alkyl amines (octylamine and oleylamine). Temperatures below 70
{\deg}C promoted the formation of monodisperse, few unit cell thick NWs that
were free from byproducts. The photoluminescence quantum yield of the NW
samples went from 12% for non-confined NWs emitting at 524 nm to a maximum of
77% for the 5 nm diameter NWs emitting at 497 nm, down to 30% for the thinnest
NWs (diameter ~ 3nm), in the latter sample most likely due to aggregation
occurring in solution.
