A study from the University of Basel demonstrates how manganese can be used to make luminescent materials and, with this, leading to the conversion of sunlight becoming more sustainable.
Manganese is a hard brittle silvery metal, often found in minerals in combination with iron. The metal is used to help render stainless steel more durable, and as manganese oxide it is used as a rubber additive, in glass making, fertilisers, and ceramics.
The new research application was based on a quest to create more sustainable luminescent materials together with catalysts for converting sunlight into other forms of energy. This has led to a new class of compounds, based on manganese. The compounds appear to possess some promising properties equivalent to those found in more expensive noble metal compounds (compounds of metallic chemical elements that have outstanding resistance to oxidation).
There is a business and technological driver for lower-cost and more sustainable compounds. For example, both smartphone screens and catalysts for artificial photosynthesis (as with biofuel production) contain very rare metals necessary for their function.
One prominent example is with iridium, which is used in organic light-emitting diodes (OLEDs). Iridium is rarer than gold or platinum. A second example is with ruthenium, which is used in solar cells.
As well as being rare, and hence expensive, these metals also tend to be environmentally damaging when mined and they are toxic in many forms, making them hard to dispose of as well as presenting a risk to manufacturing workers.
One of the reasons for turning to manganese is that the element is 900,000 times more abundant in the Earth’s crust than iridium, making it far less expensive. Moreover, obtaining manganese, partly du to its abundance, is less damaging to the environment.
To strengthen the efficacy of manganese for the types of applications that require the use of iridium, the researchers have developed several new complexes. In tests, when many of the complexes are used there is an immediate charge transfer from the manganese toward its direct bonding partners on excitation with light. Refinements of the process ensure absorbed light energy is not lost.
The efficacy will be pushed further by future research that will look at raising the luminescent properties of the new manganese complexes. In parallel, the researchers will look for ways to anchor the new complexes onto suitable semiconductor materials for use in solar cells.
The research appears in the journal Nature Chemistry, where the research comes under the heading “Manganese(i) complexes with metal-to-ligand charge transfer luminescence and photoreactivity.”
