ABSTRACT
In this study, two kinds of colloidal ternary semiconductor white light-emitting quantum dots (WQDs), Zn(0.5)Cd(0.5)S and Zn(0.8)Cd(0.2)S, are prepared and used as nanophosphors in a UV light-emitting diode (UV-LED) pumping device. When the weight ratio of Zn(0.5)Cd(0.5)S WQDs is 9.1 wt. % in silicone and the drive current is set at 20 mA, the chromaticity coordinates (CIE), correlated color temperature (CCT), color rendering index (CRI), and luminous efficiency are (0.43,0.37), 2830 K, 90, and 0.94 lm/W, respectively. On the other hand, under the same weight ratio in silicone, the CIE, CCT, CRI, and luminous efficiency of Zn(0.8)Cd(0.2)S WQDs are (0.36,0.33), 4240 K, 86, and 4.12 lm/W, respectively. Based on the above results, we can conclude that WQDs-based LED can be obtained by controlling the compositions of Zn(x)Cd(1-x)S QDs due to the coexistence of band-edge and surface state emission.
ABSTRACT
CdSe quantum dots (QDs) with the emission wavelength of 577 nm, full width at half maximum (FWHM) of 28 nm, quantum yield (QY) of 40% and average particle size of 3.7 +/- 0.5 nm are prepared. 1, 3 and 5 wt% of CdSe QDs is blended with commercial YAG:Ce phosphor (called as composite phosphor) and the device performance of YAG-based and composite phosphor-based white light-emitting diode (WLED) is investigated. The color rendering index (CRI) and luminous efficiency could be improved simultaneous for composite phosphor-based WLED. As the applied current increases, the correlated color temperature (CCT), Commission International d'Eclairage (CIE) chromaticity coordinates and CRI of both WLEDs are almost the same when compared with standard condition (20 mA), while the luminous efficiency of both WLEDs decreases with increasing applied current. It is interesting to find that there is a positive effect of QDs on the luminous efficiency and CRI value. This result also reveals that adding a small amount of yellow emitting QDs can not only reduce the scattering of light effectively but increase utilization efficiency of reflection and refraction light, thereby enhancing the efficiency of composite phosphor-based WLED. Moreover, the emission wavelength of 577 nm QDs is longer than that of YAG, it redound to extends emission range resulting in increase the CRI of devices.
ABSTRACT
This study developed a miniaturized optomechanical device (MOD) for the feasibility study of direct bilirubin in urine using high-collimation blue mini-light-emitting diodes (Mini-LEDs) as the light source. The constructed MOD used optical spectroscopy to analyze different concentrations of direct bilirubin using the absorbance spectrum to achieve a noninvasive method for detection. The experimental results showed that between the absorbance and different concentrations of direct bilirubin at the blue Mini-LEDs central wavelength (462 nm) was the optimum fitting wavelength; in the direct bilirubin concentration range from 0.855 to 17.1 µmol/L, the coefficient of determination (R2) was 0.9999, the limit of detection (LOD) of 0.171 µmol/L, and the limit of quantitation (LOQ) of 0.570 µmol/L. Therefore, we propose using blue Mini-LEDs as a light source to design a MOD to replace the invasive blood sampling method with a spectroscopic detection of direct bilirubin concentration corresponding to absorbance.
ABSTRACT
We demonstrate excellent color quality of liquid-type white light-emitting diodes (WLEDs) using a combination of green light-emitting CsPbBr3 and red light-emitting CdSe/ZnS quantum dots (QDs). Previously, we reported red (CsPbBr1.2I1.8) and green (CsPbBr3) perovskite QDs (PQDs)-based WLEDs with high color gamut, which manifested fast anion exchange and stability issues. Herein, the replacement of red PQDs with CdSe/ZnS QDs has resolved the aforementioned problems effectively and improved both stability and efficiency. Further, the proposed liquid-type device possesses outstanding color gamut performance (132% of National Television System Committee and 99% of Rec. 2020). It also shows a high efficiency of 66 lm/W and an excellent long-term operation stability for over 1000 h.
ABSTRACT
White light-emitting quantum dots (QDs) have shown brilliant prospects as a white-light source in solid-state lighting devices, however their commercial application is limited by their low fluorescence quantum yield (QY). Here, we report a facile thermal pyrolyzed organometallic route to synthesize white-light emitting CdSe QDs with enhanced QY, by employing a particular non-coordinating solvent and long carbon chain amine. By clarifying the three distinct growing stages of CdSe nanocrystals, we are able to determine the critical growth parameters for high quality magic size QDs. According to the optical measurement and advanced characterization result, the as-synthesized magic-size QD samples show an enhanced QY (up to 64%) and an ultra-high stability with no degradation even after 120 days, while the fabricated WLED devices also exhibit desirable properties (e.g., high QY and CRI, decent efficacy), demonstrating progress towards the desired efficiency of a commercially viable solid-state lighting device.
ABSTRACT
The ORR activity of Pt3M NRs is related to the oxophilicity (ΔE(ads)). However, their segregation energy when exposed to oxygen containing species (OCS*) determines their stability. Although the ΔE(ads) of Ag is not as weak as that of Au, its structure is relatively stable, thus promoting the ORR stability.
ABSTRACT
The combinational modification of the morphology, alloying, and support for Pt catalysts has been optimized towards the oxygen reduction reaction. Graphene-supported PtPd nanorods have lower unfilled Pt d-states than carbon-supported Pt nanoparticles (Pt/C) and their specific and mass activities after the accelerated durability test are about 6.5 and 2.7 times higher than those of Pt/C, attributed to the synergistic electronic modification effect and graphene-metal interaction.
ABSTRACT
This paper demonstrates a proof-of-concept approach for producing genipin-gelatin microcapsules of precisely controlled and monodisperse size distributions by the microfluidic channels. We have demonstrated that one could control the size of emulsions from 130 microm to 580 microm in diameter (with a variation of less than 5%) by altering the relative sheath/sample flow rate ratio. In addition, Results show that the encapsulation and in vitro release of a model drug, 5-fluorouracil, to enhance the effect of controlled release. We demonstrated that the appropriate particle size for different release patterns is predictable, enabling better application of genipin-gelatin microcapsules as a drug carrier. The proposed microfluidic chip is capable of generating relatively uniform micro-droplets with well controllable diameter, and it has the added advantages of being a simple, low cost, and high throughput process.