A new kind of carbon dots based phosphor is developed for light emitting diodes (LED) by adsorbing carbon dots to starch particles. The bonding mechanism is based on hydrogen bonding of surface functional groups of carbon dots and starch particles. Aggregation-induced quenching is avoided and the thermal stability of the carbon dots phosphor is enhanced. The carbon dots phosphor is used as color convert material for white LED devices. The white LED device fabricated has an ultra-high color rendering index of 93.9, almost pure white CIE coordinate at (0.332, 0.336) and moderate CCT at 5498K. The photoluminescence intensity (PL) under constant temperature and alternative condition is both tested to study the thermal stability of the phosphor. The PL intensity shows no obvious change after 3 days of aging; only 4% of PL loss after 10 cycles of 25°C /85°C alternation. Based on its good PL properties and thermal stability, this carbon dots phosphor has great potential for white LED lighting.

Based on blue LED chips to excite Ce-doped yttrium aluminum garnet (YAG: Ce 3+) yellow phosphors, InP/ZnS green-emitting quantum dots (QDs) and InP/ZnSe/ZnS red-emitting QDs are used as light conversion materials for WLEDs to improve the color rendering index (CRI) of the device and improve its color coordinates. We have proven this in previous work. But in the previous work, we only studied the CRI of the driving current from 5 mA to 100 mA. The CRI and the Commission International de L'Eclairage (CIE) chromaticity coordinates of the WLED device prepared before is not ideal under high current conditions. The emission peak position of InP/ZnSe/ZnS red-emitting QDs we used in previous work is 605nm. In this article, we adjusted the emission peak position of InP/ZnSe/ZnS red-emitting QDs to 611nm, and prepared WLED in the same way, which improved the problem that the CRI of WLED devices decreases rapidly and the chromaticity coordinates change greatly under high current conditions. The CRI of prepared WLED device in this article was increased to 91.0, the CIE chromaticity coordinates is (0.3365, 0.3334), and the correlated color temperature (CCT) is 5313 K. We also tested the dependence of the electroluminescence (EL) spectrum, CRI, CCT and chromaticity coordinates of the prepared WLED device on the current. Compared with the prepared WLED device before, the CRI of the WLED device prepared in this article has always remained above 90, hovering between 90 ~ 91, very stable. The chromaticity coordinate distribution is also very concentrated, the amplitude of the offset black body radiation is small, and it shows excellent color rendering and stable working performance. A 30-day aging test was performed on the prepared WLED device.

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