We have seen the effects of buffer layer in organic light-emitting diodes using poly(N-vinylcarbazole)(PVK). Polymer PVK buffer layer was made using static spin-casting method. Two device structures were made; one is ITO/TPD/Alq3/Al as a reference and the other is ITO/PVK/TPD/Alq3/Al to see the effects of buffer layer in organic light-emitting diodes. Current-voltage characteristics, luminance-voltage characteristics and luminous efficiency were measured with a variation of spin-casting speeds. We have obtained an improvement of luminous efficiency by a factor of two and half when the PVK buffer layer is used.

We have seen the effects of buffer layer in organic light-emitting diodes(OLEDs) using poly(N-vinylcarbazole)(PVK) depending on a concentration of PVK. Polymer PVK buffer layer was made using spin casting technique. Two device structures were fabricated; one is ITO/TPD/Alq3/Al as a reference, and the other is ITO/PVK/TPD/Alq3/Al to see the effects of buffer layer in organic light-emitting diodes. Current-voltage-luminance characteristics and an external quantum efficiency were measured with a variation of spin-casting rpm speeds and PVK concentration. We have obtained an improvement of external quantum efficiency by a factor of four when the PVK concentration is 0.1wt% is used. The improvement of efficiency is expected due to a function of hole-blocking of PVK in OLEDs.

식물묘의 생장 및 형태형성 제어용 인공광원으로서 조합광 LED 모듈을 제작하여 조합광 LED모듈의 광전기 특성을 분석하고, 광량자 센서와 분광광도계를 이용하여 LED 모듈로부터 조사된 광량자속에 대한 정량화를 시도하였다. 청색과 적생의 단색광 LED로부터 조사된 광량자속을 광량자센서로 측정한 값과 분광광도계로 측정하여 수치적으로 적분한 값을 qly한 결과 거의 일치하는 것으로 나타났다. 이러한 결과는 광량자센서로서 측정이 불가능한 원적색광 LED로부터의 광량자속 정량화에 분광광도계를 적용될 수 있음을 의미하는 것이다. 적생광에 원적색광을 조사하는 LED스틱의 혼합 비율을 달리한 조합광 LED 모듈의 광량지속은 원적색광을 조사하는 LED 스틱이 증가할수록 조합광 LED의 광량자속이 조금씩 증가하였다. 이러한 결과는 단위에너지당 조사된 광량지수는 파장에 비례해서 증가히기 때문인 것으로 해석된다. 이밖에 적색과 원적색광 LED 스틱의 조합 비율을 달리하였을 때 조합광 LED 모듈의 조도는 비시감도가 매우 낮은 원적색광이 차지하는 비율이 클수록 낮게 나타났다. 한편 적색광과 원적생광의 혼합 정도가 조합광 LED의 복사조도에 미치는 영향은 거의 없는 것으로 나타났다.

Background : Light-Emitting Diodes (LEDs) have been reported to alter the composition of the secondary metabolites present in many plants. For example, light exposure has been reported to significantly affect secondary metabolite biosynthesis in plants, and irradiance levels have been reported to affect the concentration and production of both phenylpropanoids and carotenoids. Therefore, the objective of the present study was to determine the most effective LED light source in enhancing growth and secondary metabolites (polyphenols and carotenoids) and investigate the effect of LED illumination on production the of primary and secondary metabolites (polyphenols and carotenoids) in Vigna unguiculata L. Walp. sprouts Methods and Results : In order to determine the effect of light-emitting diodes (LEDs) on plant metabolism, the present study examined the primary and secondary metabolite profiles of Vigna unguiculata L. Walp. sprouts that were exposed to red, blue, white, or a combination of red and blue LEDs using high-performance liquid chromatography (HPLC), electrospray ionization-mass spectrometry (ESI-MS), gas chromatography-mass spectrometry (GC-MS), and gas chromatography time-of-flight mass spectrometry (GC-TOF-MS). A total of 39 hydrophilic compounds were identified and quantitated using GC-TOF-MS, and six phenylpropanoids and six carotenoids were quantified using HPLC. The plants grown under blue LED light contained the highest level of total carotenoids (253.72 ± 17.27 ㎍/g) and phenylpropanoids (2,600.51 ± 4.90 ㎍/g). Thus, the current study provides a new approach for enhancing the carotenoid and phenylpropanoid production of V. unguiculata. Conclusion : This study suggests that blue LED light source is the most appropriate for the sprout growth and production of phenolic compounds and carotenoids in cowpea sprouts. Furthermore, these findings confirm that HPLC, GC-MS, and GC-TOF-MS are suitable for investigating metabolic relationships and offer a tenable strategy for enhancing secondary metabolite production using LED light sources.

Background : Nasturtium officinale L. which is commonly known as watercress is aquatic perennial herb distributed to Europe, Asia, North and South America. It consist of various nutrients and beneficial compounds such as vitamin B and C, provitamin A, folic acid, carotenoids, glucosinolates, and minerals. Recent studies have demonstrated the biological properties that include antidiabets, antiinflammatory, antioxidative, and anticancer. In this study, the effects of light-emitting diodes (LEDs) on growth and development, accumulation of phenolic compounds and glucosinolates were investigated in watercress. Methods and Results : Length of shoot and root, and fresh weight of whole plants were measured every weeks (1 to 3 weeks) after sowing. These were significantly affected by different LED lights. Normally, length of shoot and fresh weight of white- and blue-light-radiated watercress were less than those of red-light-radiated watercress. Contents of phenolic compounds and glucosinolates were investigated in watercress under different LEDs treatment by HPLC analysis. Six phenolic compounds including catechin hydrate, chlorogenic acid, caffeic acid, p-coumaric acid, trans-cinnamic acid, and kaempferol were detected. Also, eight glucosinolates that include four aliphatic glucosinolates (glucoiberin, gluconapoleiferin, glucosiberin, and glucohirsutin), three indolic glucosinolates (4-hydroxyglucobrassicin, glucobrassicin, and 4-methoxyglucobrassicin), and one aromatic glusinolate (gluconasturtiin). Mostly, white light treatment led to the higher production of their compounds than those of red- and blue-radiated. Conclusion : It is concluded that different LED lights have effect on growth rates and secondary metabolites production. Red light caused vigorous growth of shoot and affected their fresh weights. In addition, the accumulation of each compounds was varied depending on light colours and time of harvest.

The objective of this study was carried out to elucidate the effect of LEDs (light emitting diodes) irradiation in relation to early growth and inorganic elements in leaf lettuce (Lactuca sativa L. ‘Chung Chi Ma’). In morphological changes of leaves, shoot elongation and hypocotyl length showed poor growth in red light irradiation, while the red+blue light irradiation induced shorter plant height and much greater leaf numbers resulting in increased fresh weight. In change of the Hunter's color and SPAD values, lettuce seedlings grown under in red+blue and fluorescent light irradiation had a higher a* value, otherwise SPAD values were not changed in these light irradiations. Interestingly, relative chlorophyll contents showed 1.8 times increased redness in the treatment of red+blue light irradiation. Inorganic element (N, Ca, Mg, Mn, and Fe) and ascorbic acid contents were increased in lettuce plants grown under LEDs light irradiation compared to those of lettuce grown under the fluorescent light which showed higher P and Mn contents. In conclusion, it is considered that red+blue light irradiation which stimulates growth and higher nutrient uptake in leaf lettuce could be employed in containers equipped with LEDs.

The purpose of this study was to determine optimum conditions for the cultivation of Tetraselmis suecica (T. suecica) under illumination of four different types of LEDs (i.e., blue, red, white, and mixed). Initial cell concentration was 4×104 cells/mL and temperature of reactor was maintained between 21-240C. Specific growth rates were 0.72 day-1(white), 0.58 day-1(red), 0.49 day-1(mixed), and 0.49 day-1(blue). Thus, white LEDs was used for the cultivation of T. suecica. Tests with white LEDs under different light intensity, which was conducted to determine optimum light intensity of white LEDs, showed that 9,000 lux of illumination resulted in fastest cell growth and greatest cell concentrations. To avoid shadow effects by dense cell populations, aeration was performed. Cell concentration increased 3.8 times when aeration was used.

Unlike water applications, the photocatalytic technique utilizing light-emitting-diodes as an alternative light source to conventional lamp has rarely been applied for low-level indoor air purification. Accordingly, this study investigated the applicability of UV-LED to annular-type photocatalytic reactor for removal of indoor-level benzene and toluene at a low concentration range associated with indoor air quality issues. The characteristics of photocatalyst was determined using an X-ray diffraction meter and a scanning electron microscope. The photocatalyst baked at 350 ℃ exhibited the highest photocatalytic degradation efficiencies(PDEs) for both benzene and toluene, and the photocatalysts baked at three higher temperatures(450, 550, and 650 ℃) did similar PDEs for these compounds. The average PDEs over a 3-h period were 81% for benzene and close to 100% for toluene regarding the photocatalyst baked at 350 ℃, whereas they were 61 and 74% for benzene and toluene, respectively, regarding the photocatalyst baked at 650 ℃. As the light intensity increased from 2.4 to 3.5 MW cm-1, the average PDE increased from 36 to 81% and from 44% to close to 100% for benzene and toluene, respectively. In addition, as the flow rate increased from 0.1 to 0.5 L min-1, the average PDE decreased from 81% to close to zero and from close to 100% to 7% for benzene and toluene, respectively. It was found that the annular-type photocatalytic reactor inner-inserted with UV-LEDs can effectively be applied for the decomposition of low-level benzene and toluene under the operational conditions used in this study.