Luminescent materials for solid-state lighting

The 68th Session of the UN General Assembly proclaimed 2015 as the International Year of Light and Light-based Technologies (IYL 2015). Indeed, lighting is central to modern human existence, illuminating the dark and thereby permitting increased productivity and night time human activity. According to the International Energy Agency (http://www.iea.org/textbase/npsum/lll.pdf), 19% of World grid electricity production is devoted to lighting, making this sector a major consumer of energy and contributor to greenhouse gas emissions. This figure rises sharply in urban areas where up to 50% of electricity usage can be devoted to lighting. Developing and adopting energy efficient and long-lasting lighting devices, which inevitably will incorporate new materials, will thus concomitantly have a significant positive impact on the climate, reduce operational cost in the long term and improve society. Illustrative of the importance of lighting to society was the awarding of the Nobel Prize in physics in 2014 to Isamu Akasaki, Hiroshi Amano and Shuji Nakamura “for the invention of efficient blue light-emitting diodes which has enabled bright and energy-saving white light sources”.

It is thus timely that this themed issue of Dalton Transactions highlights the breadth of emissive inorganic materials used for a range of lighting applications including organic light-emitting diodes (OLEDs) and light-emitting electrochemical cells (LEECs). In this issue, the spotlight is on light-emitting complexes employing copper, gold, iridium, platinum, and rhenium. Historically, organometallic complexes have been targeted as emitters for lighting as the metal promotes intersystem crossing and phosphorescence. Consequently, electroluminescent devices incorporating these materials can attain 100% internal quantum efficiency by harvesting all the generated excitons.

An exciting direction in emitter development touched upon in this collection is the use of thermally-activated delayed fluorescent (TADF) molecules in electroluminescent devices as these too can attain similar efficiencies, yet without the need of rare and expensive metals.

Whilst it is unfortunately impossible to cover all classes of inorganic emitters in a single collection, the wide scope of emissive complexes, their diverse optoelectronic properties and their varied performance in solid-state lighting devices illustrates the challenge in rationally designing high-performance emitters. Indeed, most of the papers in this collection are multi-disciplinary, combining theoretical calculations, synthesis, a suite of optoelectronic characterization techniques as well as device fabrication and evaluation. Recruiting chemistry, physics and materials science together is what is required to meet the grand challenge of low cost, long lasting and energy efficient lighting.

I am very grateful to the editorial staff at Dalton Transactions for making this themed issue possible. I would like to thank all the authors – coming from twelve countries over four continents – for their strong contributions in supporting this issue. Clearly, research into emitter development for solid-state lighting remains vibrant and bright.

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