Colouration process of colloidal tungsten oxide nanoparticles in the presence of hydrogen gas

► Tungsten oxide nanoparticles were prepared by pulsed laser ablation (PLA). ► Hydrogen catalyst (Pd) was deposited on tungsten oxide nanoparticles surface. ► After exposing the colloidal nanoparticles to hydrogen gas coloration occurs. ► An absorption peaks (1.6 eV) appeared at the initial moments of hydrogen exposing. ► Two other peaks (1.26, 1.97 eV) become dominant at long hydrogen exposure times.