Glossary
What is the Beer-Lambert law?
Beer-Lambert's Law is the basic law of light absorption for all electromagnetic radiation and all light absorbing materials, including gases, solids, liquids, molecules, atoms and ions.
The proportion of light absorbed by the transparent medium is independent of the intensity of the incident light; each equal thickness layer of light absorbs light of the same proportional value over the optical path.
Recently, researchers at Ghent University in Belgium have discovered a hybrid LED using quantum dot technology. The LED consists of a blue LED illumination source and a non-contact hybrid fluorescent film material. The fluorescent film is mainly red cadmium selenide and cadmium sulfide. (CdSe/CdS) quantum dot material and green fluorescent material doped with europium (Eu). Since the quantum dot structure has good light conversion rate for light conversion, luminescence spectrum adjustability, narrow spectral band and the like. Therefore, the researchers believe that this hybrid structure has good performance in terms of cost and efficiency.
Research methods
The researchers used red cadmium selenide and cadmium sulfide (CdSe/CdS) quantum dot materials and green SrGa2S4:Eu2+ (STG) materials to make fluorescent films, and dissolved these materials in methyl ethyl ketone (containing a certain amount of toluene). ) in solution. At the same time, the mixed solution was plated on a thin glass piece of 18 mm in diameter by drop-casting.
For fluorescent films, researchers have designed a variety of different fluorescent film structures to evaluate the performance of LEDs.
1. Simple red-green mixed fluorescent film with structure such as |RG|;
2. A separate fluorescent film (filled with air in between) of two glass substrates was used. Structure such as |R||G| or |G||R|;
3. A structure similar to the second is used, but the middle is filled with ethylene glycol. This structure can alleviate the problem of index matching, such as |R||G| or |G||R|.
research content
Hybrid fluorescent film structure
As shown in Figure 1a, the color of the |RAGA| hybrid structure LED is 7082K, and the coordinates in CIE(X,Y) are (0.299,0.345), and the internal quantum efficiency (IQE) is 80. % (individual |R| is 71% and |G| is 93%).
At the same time, the researchers found that the light intensity attenuation of this hybrid structure is different from the individual materials. According to Figure 1d, there is almost no change in the attenuation of the STG material, but the luminous intensity of the quantum dots is guaranteed to rise throughout the decay process. This is mainly due to the direct excitation of the blue light source and the indirect excitation of the STG material.
Figure 1 Luminescence spectrum of mixed white LED
a |RA||GA|Structure spectrum
b |RA||GA| and |RA||GA|structure spectra
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