Optical properties and reliability studies of gradient alloyed green and red emitting quantum dots for white light-emitting diodes

Luminescent materials become one of interesting issues for white LED-based lighting devices (WLEDs) due to their high performances for converting the monochromatic light from UV/blue LED chips into white light. The most common... [ view full abstract ]

Luminescent materials become one of interesting issues for white LED-based lighting devices (WLEDs) due to their high performances for converting the monochromatic light from UV/blue LED chips into white light. The most common current commercial devices incorporate blue-emitting InGaN diodes around 450 nm, combined to lanthanide-based phosphors (mainly cerium-doped YAG (Y₃Al₅O₁₂: Ce³⁺) most often associated with a red emitting phosphor )which partly converts the incident blue emission into a relatively broad emission in the yellow-red, thus generating white lighting with high luminous efficiencies and suitable colorimetric qualities in terms of color correlated temperature (CCT ) and color rendering index (CRI). These phosphors contain rare-earth (RE) elements. China, which already holds 37% of rare earths world reserves, also has a near-monopoly of production (97%) and reduces export quotas each year. But global demand is growing every year by 6%, putting the market under pressure. In this context, it is now crucial to identify new cheap and REE-free phosphors capable of delivering cost-effective light energy conversion, especially in commercial white light generation.

In this talk, we will report the development of rare-earth-free luminescent nanocomposites combined with UV/blue LED chips in order to provide white light. Cadmium selenide/zinc sulfide (CdSe)_x(ZnS)_1-x and copper indium sulfide/zinc sulfide (CuInS₂)_x(ZnS)_1-x quantum dots have been used to achieve the luminescent nanocomposite films in silicone as polymer matrix. The photoluminescence properties of QDs composite films obtained by incorporating gradient alloyed (CdSe)_x(ZnS)_1-x and (CuInS₂)_x(ZnS)_1-x QDs were investigated. The photometric parameters of systems consisting of luminescent nanocomposites and LEDs including color rendering index (CRI), correlated color temperature (CCT), chromaticity coordinates, and luminous efficacy which can be tuned by controlling the compositions and thickness of nanocomposite films, will be presented. Moreover, the reliability of QDs composite films was evaluated by collecting the photoluminescence (PL) intensity upon LED excitation at 375 nm or 450 nm, for different irradiation powers and different temperatures. The obtained behaviors will be discussed.