Fabrication and performance of dual-wavelength white lightemitting diodes assisted with red-emitting nanocrystals

The yellow-emitting phosphor excited by blue chip has low color rendering index (CRI) and high correlated color temperature (CCT), due to the lack of the red light emission in the spectrum. Moreover, those phosphors have micron size, resulting in not only serious internal scattering and bad tunable wavelength but also lower conversion efficacy. Accordingly, the luminous efficacy of white light-emitting diode (WLED) decreases with the addition of micron phosphors. Therefore, in order to increase the luminous efficacy of WLED without losing CRI, the semiconductor nanocrystals (NCs) have been used in this study. In order to exploring the characteristic of WLED devices, the blue chip has been used as excitation source to pump the phosphors, which are blended with the green/red-emitting phosphors and ternary alloyed red-emitting ZnCdSe NCs, having the emission wavelength of 632 nm and quantum yield (QY) of 24 %. Besides, when the weight ratio of red-emitting phosphor (CaSiAlN3:Eu) in the green-emitting phosphor (Lu₃Al₅O₁₂:Ce) increases from 0 to 11 wt%, the device performance such as the Commission International d'Eclairage (CIE) chromaticity coordinates shifts from (0.32,0.43) to (0.48,0.39), CRI increases from 64 to 81, and the luminous efficacy drops from 60 to 48 lm/W. Moreover, when the weight ratio of red-emitting phosphor is 5 wt%, it shows a device performance with that the CIE is (0.41,0.42), CRI is 81 and device efficacy is 53 lm/W. On the other hand, when 3 wt% of ZnCdSe NCs is blended with the green/red-emitting phosphors (5 wt% red-emitting phosphor in green-emitting phosphor), it increases 8 % of the luminous efficacy and 1 % of CRI when compared to the original green/red phosphorbased WLED.