White light emission from blue InGaN LED precoated with conjugated copolymer/quantum dots as hybrid phosphor

Abstract

In this work we fabricated white LEDs using a blue InGaN LED precoated conjugated copolymer/quantum dots (QDs) composite (green-emitting Poly {(9,9-dioctyl-2,7-divinylenefluorenylene)-alto-co-(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene)}/red-emitting CdSe quantum dots) as a hybrid phosphor. The emission peak wavelengths of the blue and red emissions in the spectra were 462 and 618 nm, respectively. The green-emitting polymer had two emission peaks at 515 and 543 nm. The subpeak of the copolymer (515 nm) was decreased by the absorption of QDs as the ratio of QDs increased, while the emission of the QD (618 nm) increased. Therefore, changes in the CIE-1931 coordinate, color temperature (Tc) and color-rendering index (Ra) were dependent on the QDs to copolymer ratios. The white LED of the hybrid phosphor containing 20 wt.% QDs had a luminous efficiency of 44.21 m/W at 20 mA with a CIE-1931 coordinate, Tc and Ra of (0.3297, 0.3332), 5620 K and 75.3, respectively. (C) 2009 Elsevier B.V. All rights reserved.