New structure of white backlight LED - quantum dot hybrid LED

**Glossary** What exactly is the Beer-Lambert Law? The Beer-Lambert Law serves as the fundamental principle governing light absorption across all forms of electromagnetic radiation and various light-absorbing materials, including gases, solids, liquids, molecules, atoms, and ions. It states that the proportion of light absorbed by a transparent medium is independent of the intensity of the incident light. Instead, each equal thickness layer of light absorbs light in the same proportional manner along the optical path. Recently, scientists at Ghent University in Belgium have developed a hybrid LED utilizing quantum dot technology. This innovative LED comprises a blue LED as its illumination source paired with a non-contact hybrid fluorescent film. The fluorescent film primarily consists of red cadmium selenide and cadmium sulfide (CdSe/CdS) quantum dot material, along with green fluorescent material doped with europium (Eu). Given the excellent light conversion efficiency, luminescence spectrum adjustability, and narrow spectral bandwidth offered by quantum dot structures, the researchers believe this hybrid configuration demonstrates impressive performance in terms of both cost-effectiveness and efficiency. **Research Methods** To create the fluorescent films, the researchers employed red cadmium selenide and cadmium sulfide (CdSe/CdS) quantum dot materials alongside green SrGa₂S₄:Eu²⁺ (STG) materials, dissolving them in a solution of methyl ethyl ketone (mixed with a specific amount of toluene). They then applied the mixture onto a thin glass disc measuring 18mm in diameter via drop-casting. For the fluorescent films, the team designed multiple distinct configurations to assess their impact on LED performance. These included a simple red-green mixed fluorescent film structured as |RG|, separate fluorescent films (with air gaps between them) structured as |R||G| or |G||R|, and a similar setup but with ethylene glycol filling the gap to address index-matching issues, structured as |R||G| or |G||R|. **Research Content** **Hybrid Fluorescent Film Structure** As illustrated in Figure 1a, the |RAGA| hybrid structure LED exhibits a color temperature of 7082K, with coordinates in CIE(X,Y) at (0.299, 0.345), and an internal quantum efficiency (IQE) of 80% (with individual IQEs of 71% for |R| and 93% for |G|). Simultaneously, the researchers noted a unique behavior regarding the light intensity attenuation of this hybrid structure compared to individual materials. As depicted in Figure 1d, the STG material showed minimal change in attenuation, while the luminous intensity of the quantum dots consistently increased throughout the decay process. This phenomenon can be attributed to the direct excitation of the blue light source and the indirect excitation of the STG material. Figure 1 presents the luminescence spectrum of the mixed white LED. The first image (a) shows the spectrum of the |RA||GA| hybrid structure, while the second image (b) compares the spectra of |RA||GA| and another configuration. These visualizations underscore the effectiveness of the hybrid approach in achieving balanced and efficient luminescence. This research not only advances our understanding of quantum dot applications but also opens new avenues for optimizing LED efficiency and performance in future technologies.

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