New structure of white backlight LED - quantum dot hybrid LED

### Glossary What exactly is the Beer-Lambert law? The Beer-Lambert law is a fundamental principle governing the absorption of electromagnetic radiation across all types of light-absorbing materials, whether they are gases, solids, liquids, molecules, atoms, or ions. This law states that the proportion of light absorbed by a transparent medium is independent of the intensity of the incident light. In other words, each equal thickness of the medium will absorb light in the same proportional manner along the optical path. Recently, researchers at Ghent University in Belgium have developed a novel hybrid LED utilizing quantum dot technology. This LED combines a blue LED as its illumination source with a non-contact hybrid fluorescent film made of specific materials. The fluorescent film primarily comprises red cadmium selenide and cadmium sulfide (CdSe/CdS) quantum dots alongside green fluorescent material doped with europium (Eu). Given the excellent light conversion efficiency, tunable luminescence spectrum, and narrow spectral bandwidth of quantum dots, the researchers believe this hybrid structure offers significant advantages in terms of both cost and efficiency. ### Research Methods To create the fluorescent films, the researchers employed red cadmium selenide and cadmium sulfide (CdSe/CdS) quantum dots along with green SrGa₂S₄:Eu²⁺ (STG) materials. These were dissolved in a solution of methyl ethyl ketone (mixed with a specified amount of toluene). The resulting mixture was then applied to a thin glass disc with a diameter of 18 millimeters using the drop-casting method. For the fluorescent films, various structural designs were created to evaluate their performance in enhancing LED efficiency. These included: 1. A simple red-green mixed fluorescent film structured as |RG|; 2. Two separate fluorescent films placed on individual glass substrates, separated by air, structured as |R||G| or |G||R|; 3. A similar structure to the second case but filled with ethylene glycol to address refractive index matching issues, structured as |R||G| or |G||R|. ### Research Content #### Hybrid Fluorescent Film Structure As illustrated in Figure 1a, the hybrid structure |RAGA| exhibits a correlated color temperature (CCT) of 7082K, with CIE chromaticity coordinates of (0.299, 0.345). Its internal quantum efficiency (IQE) reaches 80%, with individual components showing IQEs of 71% for |R| and 93% for |G|. The researchers also observed distinct differences in the light intensity decay characteristics of this hybrid structure compared to the individual materials. As depicted in Figure 1d, the STG material shows minimal variation in light intensity decay, while the quantum dots maintain an increasing light intensity 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 displays the emission spectrum of the mixed white LED.  **a |RA||GA| Structure Spectrum**  **b Comparison of |RA||GA| and |RA||GA| Structure Spectra** This research not only demonstrates the potential of quantum dot technology in enhancing LED performance but also highlights the importance of carefully designing hybrid structures to optimize light output and efficiency. Future work may explore further improvements in the refractive index matching and long-term stability of these hybrid systems, which could lead to even more efficient and versatile lighting solutions.

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