Researchers at Australia's Griffith University have discovered a fascinating mechanism, that may allow the design of a new class of composite materials for light harvesting and optoelectronics. The team has found a quantum-confined bandgap narrowing mechanism, where UV absorption of the graphene quantum dots and TiO2 nanoparticles can easily be extended into the visible light range.

According to the scientists, real life application of this would be high efficiency paintable solar cells and water purification using sun light. In addition, the team states that "this mechanism can be extremely significant for light harvesting. What's more important is we've come up with an easy way to achieve that, to make a UV absorbing material to become a visible light absorber by narrowing the bandgap."

Many efforts have been made to improve titania's absorption of visible light or develop visible-light sensitive materials in general. Methods used for titania usually require strict conditions to obtain the modified TiO2 such as elevated temperature or high pressure. In their innovative paper, the researchers observed that when TiO2 particles are mixed with graphene quantum dots, the resulting composite absorbs visible light by a quantum-confined bandgap narrowing mechanism.

When two materials were mixed together, they started to absorb in the visible range, more significantly, the bandgap can be tuned by the size of graphene quantum dots. The team named the phenomenon 'quantum-confined bandgap narrowing' and this mechanism may be applicable to all semiconductors, when they are linked with graphene quantum dots.