Molybdenum blues with tunable light absorption synthesized by femtosecond laser irradiation of molybdenum trioxide in water/ethanol mixtures

Molybdenum blues (MBs) have attracted increasing attention due to their tunable structures and properties, which make them applicable in numerous fields. In this work, a novel strategy to synthesize MB nanorings by irradiating MoO₃ suspended in water/ethanol mixtures with intense femtosecond laser pulses is demonstrated. It is found that the MoO₃ can be dissolved in the water during laser irradiation to form molybdic acid, which provides an acidic environment for the formation of MB. Concentrations of ethanol as low as 1% result in the formation of MB and by adjusting the concentration of ethanol in the solvent, the absorption band can be tuned due to the modification of Mo^VOMo^VI entities. The MB synthesized in 30% ethanol appears the darkest blue and assembly of vesicles 115 nm in size is observed. At high concentrations of ethanol (>70%), H_XMoO₃ and MoO_3-X are preferentially formed instead of MB. The photothermal conversion efficiency of the MBs synthesized in 1% and 30% ethanol is above 40%.