Featured article: White light generation using CdSe/ZnS core-shell nanocrystals hybridized with InGaN/GaN light emitting diodes

We introduce white light generation using CdSe/ZnS core–shell nanocrystals of single, dual, triple and quadruple combinations hybridized with InGaN/GaN LEDs. Such hybridization of different nanocrystal combinations provides the ability to conveniently adjust white light parameters including the tristimulus coordinates (x, y), correlated colour temperature (Tc) and colour rending index (Ra). We present the design, growth, fabrication and characterization of our white hybrid nanocrystal-LEDs that incorporate combinations of (1) yellow nanocrystals (λPL = 580 nm) on a blue LED (λEL = 440 nm) with (x, y) = (0.37, 0.25), Tc = 2692 K and Ra = 14.69; (2) cyan and red nanocrystals (λPL = 500 and 620 nm) on a blue LED (λEL = 440 nm) with (x, y) = (0.37, 0.28), Tc = 3246 K and Ra = 19.65; (3) green, yellow and red nanocrystals (λPL = 540, 580 and 620 nm) on a blue LED (λEL = 452 nm) with (x, y) = (0.30, 0.28), Tc = 7521 K and Ra = 40.95; and (4) cyan, green, yellow and red nanocrystals (λPL = 500, 540, 580 and 620 nm) on a blue LED (λEL = 452 nm) with (x, y) = (0.24, 0.33), Tc = 11 171 K and Ra = 71.07. These hybrid white light sources hold promise for future lighting and display applications with their highly adjustable properties. Lighting poses an increasing market demand as one of the next great solid-state frontiers [1]. For that, white light emitting diodes (WLEDs) have attracted both scientific attention and commercial interest with their potential widescale use, for example, in architectural lighting, decorative lighting, flashlights and backlighting of large displays [2]. To date, multi-chip WLEDs, monolithic WLEDs and colourconversion WLEDs, commonly with yellow phosphorus, have been extensively exploited [3–5]. Also, as an alternative approach, nanocrystals (NCs) have recently been used for colour conversion in white light generation; a blue/green twowavelength InGaN/GaN LED coated with a single type of red NC and a blue InGaN/GaN LED with a single type of yellow NC and a dual type with red and green NCs have been reported [6–9]. In the most common approach of colour-conversion WLEDs coated with phosphorus, although phosphorus is good for photoluminescence across the visible, its emission spectrum is fixed. On the other hand, the use of combinations of nanocrystals provides the ability to adjust the white light parameters. To this end, in this work for the first time, we present white light generation with adjustable parameters using multiple combinations of NCs, each of which features a narrow emission spectrum widely tunable across the visible spectral range. Hybridizing CdSe/ZnS core–shell NCs of various single, dual, triple and quadruple combinations with InGaN/GaN LEDs, we demonstrate white light generation with adjustable tristimulus coordinates, correlated colour temperature and colour rending index. Here we present the design, epitaxial growth, fabrication and characterization of 0957-4484/07/065709+05$30.00 1 © 2007 IOP Publishing Ltd Printed in the UK Nanotechnology 18 (2007) 065709 S Nizamoglu et al