Organic light sources look forward to optimize the photosynthesis process Valeria Fattori a , J.A. Gareth Williams b , Lisa Murphy b , Massimo Cocchi a , Jan Kalinowski c, * a Institute of Organic Synthesis and Photoreactivity, National Research Council of Italy (ISOF-CNR), via P. Gobetti 10, I-40129 Bologna, Italy b Department of Chemistry, University of Durham, South Road, Durham DH1 3LE, UK c Department of Molecular Physics, Gdan ´sk University of Technology, ul. G. Narutowicza 11/12, 80-952 Gdan ´sk, Poland Received 27 August 2008; received in revised form 9 October 2008; accepted 10 October 2008 Available online 17 October 2008 Abstract We introduce a series of organic LEDs that exploit the monomer and excimer emissions from single phosphor dopant emitters. These organic LEDs were found to be effective in the simultaneous creation of blue and red emission bands essential for plant growth. By varying the concentration of novel phosphorescent dopants selected from a series of newly synthesized platinum complexes [PtL 22–25 Cl], we have manufactured the blue-biased LEDs [with the Commission Internationale de L’Eclairage (CIE) coordinates (x, y) (0.27, 0.37)] and the red-biased LEDs [CIE coordinates (0.53, 0.38)], at a high luminance of 500 cd/m 2 and with external electroluminescence (EL) quantum efficiency of 15–18% photon/electron (! power efficiency 8–12 lm/W). The EL spectrum most suitable for the action spectrum of photosynthesis yield was that of a device incorporating 20 wt.% content of [PtL 23 Cl]. This LED yielded photosynthetic photon flux (PPF) approaching 10 mmol s 1 W 1 of the electrical power, a value which significantly exceeds that for the professional lamps used commonly for horticultural lighting. # 2008 Elsevier B.V. All rights reserved. PACS : 78.60.Fi; 78.66.Qn; 85.60.Jb; 87.50.wj Keywords: Organic electroluminescence; Organic light-emitting-diodes; Photosynthesis; Plant growth light 1. Introduction Light is essential for plant growth [1–3]. Plants have a completely different sensitivity to light colors from that of the human eye. Only a small amount of natural light (global radiation) is used by plants for growth and this is called growth light. The majority of the sunlight is heat. When a supplemental, artificial light is used to enhance growth, its source is expected to produce growth light efficiently. The most revolutionary plant lighting sources are light-emitting-diodes (LEDs). LEDs enable researchers and agriculturists to eliminate those wavelengths within normal white light that are inactive in photosynthesis, thus reducing the amount of energy required to power the plant growth lamps. With the development of ever improving light-emitting- diodes (LEDs) for lighting over the last decade, it is finally becoming economical to use LEDs as growth lights (cf. the NASA LED ultimate grow light). They can be used in any application – hydroponics or soil, home or greenhouse. Researchers of NASA’s Kennedy www.elsevier.com/locate/photonics Available online at www.sciencedirect.com Photonics and Nanostructures – Fundamentals and Applications 6 (2008) 225–230 * Corresponding author. Tel.: +48 58 664 6535; fax: +48 58 664 6535. E-mail address: kalino@polnet.cc (J. Kalinowski). 1569-4410/$ – see front matter # 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.photonics.2008.10.002