A solar energy conversion niobium oxynitride microcone and a method of the synthesis and use of niobium oxynitride microcones are provided. The material is useful for solar energy conversion, optics, photocatalysis, electrochromics, sensors and biomedical applications. According to one embodiment, Nb205 microcones are formed by anodization of (1M NaF and 1 wt. % HF electrolyte −40 V −20 min), they were annealed in ammonia gas to allow their doping with nitrogen. Nitridation of the micro cones shifts the absorption edge from 450 nm for the oxide form to 777 nm for the oxynitride form.