Pulsed-laser micropatterned quantum-dot array for white light source
Sheng-Wen Wang,1 Huang-Yu Lin,1 Chien-Chung Lin,2 Tsung Sheng Kao,a,1 Kuo-Ju Chen,1 Hau-Vei Han,1 Jie-Ru Li,1 Po-Tsung Lee,1 Huang-Ming Chen,1 Ming-Hui Hong,3 and Hao-Chung Kuob,1
Abstract
In this study, a novel photoluminescent quantum dots device with laser-processed microscale patterns has been demonstrated to be used as a white light emitting source. The pulsed laser ablation technique was employed to directly fabricate microscale square holes with nano-ripple structures onto the sapphire substrate of a flip-chip blue light-emitting diode, confining sprayed quantum dots into well-defined areas and eliminating the coffee ring effect. The electroluminescence characterizations showed that the white light emission from the developed photoluminescent quantum-dot light-emitting diode exhibits stable emission at different driving currents. With a flexibility of controlling the quantum dots proportions in the patterned square holes, our developed white-light emitting source not only can be employed in the display applications with color triangle enlarged by 47% compared with the NTSC standard, but also provide the great potential in future lighting industry with the correlated color temperature continuously changed in a wide range.
Recently the light-emitting diode (LED) with white-light emission has become a key component in optoelectronic applications, especially for the low power-consumption lighting devices and full-color displays. Currently, the most common method for the white-light LED fabrication in industrials is the use of the gallium nitride (GaN) based blue LEDs to pump yellow phosphors1,2. Phosphor-based white-light LEDs provide the high efficiency light emission performance and are usually employed as the backlight source in displays . This approach is efficient and cost effective. Although the correlated color temperature (CCT) of the light emitted from phosphor-based white-light LEDs can be continuously tuned in a wide range with different phosphor doping concentrations, their color gamut is still limited and cannot reproduce the natural colors3,4,5. To enlarge the color gamut, many new phosphor materials with narrow emission bandwidth have been developed and can be mixed together to render the natural white-light emission6,7.
Colloidal quantum dots (QDs), because of their significant features such as the narrow emission bandwidth, broad absorption spectrum and tunable size quantization effect, have been extensively developed and applied for the display applications8. For example, Chen et al. used the spray coating method to separate the different color-emissions QDs on a 2-inch glass substrate, generating a large homogeneous white light emission plate as a backlight9. Recently, an alternative technique for deploying QDs which is called the quantum dot enhancement film (QDEF) provides a straightforward application in the integration with the existing display manufacturing processes. The amount and ratio of QDs with different color emissions determine the final color specification10. However, the mixture of different quantum-dots may cause significantly reabsorption effect, leading to the CIE change and the efficiency reduction of constitute QDs11,12,13.
In this paper, we exploit the pulsed laser direct writing and aerosol jet (AJ) spray coating techniques to develop a novel photoluminescent quantum dots device with microscale patterns for the uses as a white light emitting source14. The pulsed laser ablation technique15,16,17 was employed to directly fabricate microscale square holes with nano-ripple structures onto the sapphire substrate of a flip-chip blue light-emitting diode, confining sprayed quantum dots into well-defined areas and eliminating the coffee ring effect. The AJ spray coating method is a mask-free technique and can be used to reduce the volume of QD films, decrease the consumption of QDs, and easily deposit QDs on target areas with determined QDs proportions18. With these two advanced techniques, QDs of different color emissions can be sprayed at specific areas with proportional compositions and separated to prevent the interactions between each other. With a flexibility of controlling the quantum dots proportions in the patterned square holes, our developed white-light emitting source not only can be employed in the display applications, but also provide the great potential in future illumination industry.
Results and Discussion
In the process of fabricating the developed white-light LED, a flip-chip blue LED was prepared to be used as a light emitting source to irradiate the sprayed ZnS and CdSe QDs for green and red light emission, respectively .............
Conclusion
QD-based white-light LEDs with a microscale square holes array have been successfully demonstrated for white light emission by employing the pulsed laser ablation and the AJ printing techniques. After the laser treatment, the bottom of the microholes formed a nano-rippled surface with hydrophobic characteristics, and the coffee ring effect was eliminated because the QD droplets were concentrated in a specific area. The EL results, shows that the QD WLEDs exhibited stable emission upon being driven by different currents . The CCT of the QD WLEDs shifted from 6000 K to 7500 K when the current increased from 1 mA to 50 mA because of the saturation of the emission intensity of the QDs with the increase in driving current. In addition to the illumination applications, the maximum color gamut of using our QD-based white-light LEDs is enlarged and greater than the standard NTSC color gamut by 47%. In conclusion, with the pulsed laser ablation method and the AJ printing techniques, arbitrarily structural design and proportional QD addition make the developed QD white-light LEDs benefit for the future applications both in display and lighting industries.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4804257/
......whole article worth a read and food for thought, imo
Sheng-Wen Wang,1 Huang-Yu Lin,1 Chien-Chung Lin,2 Tsung Sheng Kao,a,1 Kuo-Ju Chen,1 Hau-Vei Han,1 Jie-Ru Li,1 Po-Tsung Lee,1 Huang-Ming Chen,1 Ming-Hui Hong,3 and Hao-Chung Kuob,1
Abstract
In this study, a novel photoluminescent quantum dots device with laser-processed microscale patterns has been demonstrated to be used as a white light emitting source. The pulsed laser ablation technique was employed to directly fabricate microscale square holes with nano-ripple structures onto the sapphire substrate of a flip-chip blue light-emitting diode, confining sprayed quantum dots into well-defined areas and eliminating the coffee ring effect. The electroluminescence characterizations showed that the white light emission from the developed photoluminescent quantum-dot light-emitting diode exhibits stable emission at different driving currents. With a flexibility of controlling the quantum dots proportions in the patterned square holes, our developed white-light emitting source not only can be employed in the display applications with color triangle enlarged by 47% compared with the NTSC standard, but also provide the great potential in future lighting industry with the correlated color temperature continuously changed in a wide range.
Recently the light-emitting diode (LED) with white-light emission has become a key component in optoelectronic applications, especially for the low power-consumption lighting devices and full-color displays. Currently, the most common method for the white-light LED fabrication in industrials is the use of the gallium nitride (GaN) based blue LEDs to pump yellow phosphors1,2. Phosphor-based white-light LEDs provide the high efficiency light emission performance and are usually employed as the backlight source in displays . This approach is efficient and cost effective. Although the correlated color temperature (CCT) of the light emitted from phosphor-based white-light LEDs can be continuously tuned in a wide range with different phosphor doping concentrations, their color gamut is still limited and cannot reproduce the natural colors3,4,5. To enlarge the color gamut, many new phosphor materials with narrow emission bandwidth have been developed and can be mixed together to render the natural white-light emission6,7.
Colloidal quantum dots (QDs), because of their significant features such as the narrow emission bandwidth, broad absorption spectrum and tunable size quantization effect, have been extensively developed and applied for the display applications8. For example, Chen et al. used the spray coating method to separate the different color-emissions QDs on a 2-inch glass substrate, generating a large homogeneous white light emission plate as a backlight9. Recently, an alternative technique for deploying QDs which is called the quantum dot enhancement film (QDEF) provides a straightforward application in the integration with the existing display manufacturing processes. The amount and ratio of QDs with different color emissions determine the final color specification10. However, the mixture of different quantum-dots may cause significantly reabsorption effect, leading to the CIE change and the efficiency reduction of constitute QDs11,12,13.
In this paper, we exploit the pulsed laser direct writing and aerosol jet (AJ) spray coating techniques to develop a novel photoluminescent quantum dots device with microscale patterns for the uses as a white light emitting source14. The pulsed laser ablation technique15,16,17 was employed to directly fabricate microscale square holes with nano-ripple structures onto the sapphire substrate of a flip-chip blue light-emitting diode, confining sprayed quantum dots into well-defined areas and eliminating the coffee ring effect. The AJ spray coating method is a mask-free technique and can be used to reduce the volume of QD films, decrease the consumption of QDs, and easily deposit QDs on target areas with determined QDs proportions18. With these two advanced techniques, QDs of different color emissions can be sprayed at specific areas with proportional compositions and separated to prevent the interactions between each other. With a flexibility of controlling the quantum dots proportions in the patterned square holes, our developed white-light emitting source not only can be employed in the display applications, but also provide the great potential in future illumination industry.
Results and Discussion
In the process of fabricating the developed white-light LED, a flip-chip blue LED was prepared to be used as a light emitting source to irradiate the sprayed ZnS and CdSe QDs for green and red light emission, respectively .............
Conclusion
QD-based white-light LEDs with a microscale square holes array have been successfully demonstrated for white light emission by employing the pulsed laser ablation and the AJ printing techniques. After the laser treatment, the bottom of the microholes formed a nano-rippled surface with hydrophobic characteristics, and the coffee ring effect was eliminated because the QD droplets were concentrated in a specific area. The EL results, shows that the QD WLEDs exhibited stable emission upon being driven by different currents . The CCT of the QD WLEDs shifted from 6000 K to 7500 K when the current increased from 1 mA to 50 mA because of the saturation of the emission intensity of the QDs with the increase in driving current. In addition to the illumination applications, the maximum color gamut of using our QD-based white-light LEDs is enlarged and greater than the standard NTSC color gamut by 47%. In conclusion, with the pulsed laser ablation method and the AJ printing techniques, arbitrarily structural design and proportional QD addition make the developed QD white-light LEDs benefit for the future applications both in display and lighting industries.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4804257/
......whole article worth a read and food for thought, imo
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