Open Access
Add to BibSonomyAbstract
An optically efficient liquid-crystal display (LCD) structure using a patterned quantum dot (QD) film and a short-pass filter (SPF) was proposed and fabricated. The patterned QD film contributed to the generation of 95% in the area ratio (or 90% in the coverage ratio) of the Rec. 2020 color gamut. This was achieved by avoiding the problem of interaction between white backlight and broad transmittance spectra of color filters (CFs) as seen in a conventional LCD with a mixed QD film as a reference. The patterned QD film can maintain the narrow bandwidth of the green and the red QD colors before passing through the CFs. Additionally, the optical intensities of the red, green, and blue spectra were enhanced to 1.63, 1.72, and 2.16 times the reference LCD values, respectively. This was a result of separated emission of the red and green patterned QD film and reflection of the red and green light to the forward direction by the SPF.
© 2017 Optical Society of America
1. Introduction
Liquid-crystal displays (LCDs) dominate the display market because of their various advantages such as high resolution, low power consumption, long lifetime, and low cost. In addition, owing to significant developments in manufacturing technology, it is the most suitable structure for mass production of both large-sized displays and next-generation 4K- or 8K-resolution displays. However, conventional LCDs with backlights based on blue light emitting diodes (LEDs) and yellow phosphors have technical limits to realizing a wide color gamut because of wide emission spectrum of yellow phosphors and broad transmittance spectrum of the color filters (CFs). This color limit will be critical in the near future because of Recommendation BT. 2020 (Rec. 2020) issued by the International Telecommunications Union (ITU), which specifies parameters for ultra-high-definition television [1]. The Rec. 2020 color gamut demands approximately 134% of the National Television Standard Committee (NTSC) color gamut in Commission Internationale de l’Eclairage (CIE) 1931 color space in order to ensure better visual quality through the accurate representation of the true color of objects. To widen the color gamut of LCDs, a backlight composed of red, green, and blue (RGB) tri-chip LEDs was proposed to render the white color. This resulted in a color gamut covering 105% of the NTSC standard in the CIE 1931 color space [2]. However, this model does not attain the Rec. 2020 color gamut. It also has other drawbacks including the high cost of the LCD backlight as a result of using separate driving circuits, and the requirement of advanced technology to create high-efficiency green LEDs. New types of red and green phosphors with narrow emission spectra [3–5] and the optimization of the transmittance spectra of the CFs [6, 7] were also developed; they represented the enhancement of the color gamut as compared to conventional backlight based on yellow phosphors and blue LED chips. However, these approaches are also not sufficient to meet the Rec. 2020 color gamut requirements and have relatively low optical efficiency. In addition, RGB monochromatic lasers as light sources can help realize the Rec. 2020 color gamut; however, laser-based displays have the disadvantages of high cost and speckle problems [8, 9]. In order to suppress the crosstalk between RGB CFs, the addition of a functional reflective polarizer to the LCD backlight was proposed. The resultant LCD achieved 115% of the NTSC color gamut in CIE 1976 color space, which is equivalent to 76% of the Rec. 2020 color gamut [10].
Recently, quantum dots (QDs) have been used as next-generation LCD backlight sources. They provide a wide color gamut owing to their narrow emission spectra, easy control of the emission spectrum, high quantum yield, and broad absorption spectra [11–13]. Mixed red and green QD composites dispersed in a polymer resin have been applied to LCD backlights with three different structures: 1) within the blue LED package [14–17], 2) between the blue LED package and the light guide plate (LGP) with a rail form [18, 19], and 3) on the surface of the LGP in the form of a film, as shown in Fig. 1(a) [20–22]. By downconverting blue light to red and green light, LCDs prepared using mixed QD films experimentally achieved a maximum of 109% of the NTSC color gamut in CIE 1931 color space, which is equivalent to 81% of the Rec. 2020 color gamut. However, there are two technical issues related to the color gamut and optical efficiency in the LCD with mixed QD films. The first is the limit of the color gamut due to the interactions between the spectrum of white backlight and the broad transmittance spectra of the CFs. Because white light from the blue LED chips and mixed QD films passes through each CF, a crosstalk due to an overlap in the transmittance spectra of CFs can reduce the purity of the RGB color. The second issue is that of low optical efficiency, which is due to absorption loss in the CF and reabsorption of green light by red QDs. From the experimental data, only approximately 18, 39, and 24% of white backlight is used after passing through the RGB CFs due to the absorption loss of unmatched color light in the CFs. In addition, owing to the slight overlap between the absorption spectrum of red QDs and the emission spectrum of green QDs, the reabsorption of green light by red QDs occurs in mixed QD films, which further reduces the optical efficiency.
Fig. 1 Schematic illustration of (a) a conventional LCD with a mixed QD film, and (b) our proposed LCD with a patterned QD film and an SPF.
In this study, we proposed a new LCD structure composed of patterned QD films and a short-pass filter (SPF) that experimentally realized 95% of the Rec. 2020 color gamut and enhanced the optical efficiency as compared to the LCD with mixed QD film. As shown in Fig. 1(b), in the proposed LCD, also called patterned-QD-LCD, the patterned red and green QD films are fabricated to be aligned to the red and green CFs, respectively. Thus, they are capable of downconverting blue light to red or green light, separately, resulting in both a wide color gamut and high optical efficiency. In addition, the SPF inserted at the bottom of the patterned QD film reflects red and green light to the forward direction, further improvement of optical efficiency.
2. Core components and design concept
To employ the patterned QD films in an LCD device, it is important to fabricate a thin film of both red and green QD patterns on the same substrate with high concentration of QDs. In our experiments, nonpolar ligand-capped CdSe/ZnS red and green QDs of core/shell structure with 625- and 515-nm peak emission wavelengths, respectively, were used following dispersion in a negative photoresist (SU-8, MicroChem). The patterned red and green QD films were fabricated using the photolithography process published in our previous studies [23, 24]. To fabricate patterned red and green QD films with a specific thickness (i.e., 4 µm, which is twice the thickness of that used in previous studies), the time for pre-baking, UV exposure, post-exposure baking, and developing was increased and optimized to achieve clear patterns. Following the removal of a residual layer using oxygen plasma (ZEPTO, Diener), the patterned red and green QD films with 4-µm thickness and 20 wt% of QDs were fabricated onto the glass substrate for use in this experiment.
The short-pass filter (SPF) is a kind of distributed Bragg reflector, which is composed of multiple pairs of two alternating layers with different refractive indices [25,26]. The SPF has wavelength-dependent transmission characteristics that can be altered by changing the material and thickness of the dielectric layers. Figure 2 shows the transmittance of the SPF as measured by a spectrophotometer (U-3900, HITACHI, Japan) as a function of wavelengths between 400 nm and 700 nm, and the normalized emission spectra of the blue LED, red QD film, and green QD film. The SPF was selected after considering the emission properties of the blue LED and the QD films. The SPF (FF01-498, Semrock) used in this experiment transmits only blue light (i.e., wavelengths below 500 nm) and reflects green and red light (i.e., wavelengths above 500 nm).
Fig. 2 Transmittance of the SPF measured using a spectrophotometer and the normalized emission spectra of the blue LED, red QD film, and green QD film.
The operating mechanism of the LCD with the patterned QD film and the SPF is explained in Fig. 3. The blue light from the blue LED chip passes into the SPF in a roughly vertical direction with the aid of prism sheets. It passes through the SPF with little loss, and is downconverted to red and green light after passing through the patterned red and green QDs. Subsequently, the forward-emitted light from the red and green QDs passes through each matched CF and the backward-emitted light from the QDs is reflected by the SPF to the forward direction, which results in higher optical efficiency.
3. Results and discussion
3.1 Optical efficiency
In Fig. 4(a), the schematic configuration of two different cases is shown: 1) the reference LCD with a mixed QD film and 2) a newly prepared sample LCD with the patterned QD film and the SPF. To realize the LCD with the patterned QD film and the SPF, we replaced the mixed QD film with a diffuser and moved the position of the top polarizer onto the liquid crystal (LC) layer, which means below the CF array. The CF array and the patterned QD film were assembled by placing both glass substrates outside, ensuring that vertical alignment is maintained under the optical microscope, and by subsequently attaching the SPF under the glass substrate of the patterned QD film. Figure 4(b) shows the components of the measurement system assembled for this experiment. The backlight consisted of a dot-printed LGP with dimensions 50 × 70 × 3 mm, an aluminum bottom-chassis, five blue LEDs (emission peak of 445 nm, Samsung LED) operated at 500 mA, and three commercial optical sheets (such as reflectors, diffusers, and prisms). Additionally, the measurement system included an SPF with a 25-mm diameter, a CF array with an RGB subpixel size of 40 × 115 µm, and a patterned QD film with the same size as a subpixel of the CF array. A mixed QD film, composed of red and green QDs, called a quantum dot enhancement film from 3M, was used. The measurement system was covered in black tape. A hole of 20-mm diameter was made in the tape to create an active area, thereby ensuring that only light that passed through it was measured.
Fig. 4 (a) Schematic illustration of the measurement configuration for optical intensity of an LCD with a mixed QD film (for reference) and that of an LCD with both a patterned QD film and an SPF and (b) real images of the components of the measurement system such as LGP with a reflector, a diffuser, a prism, a polarizer, an SPF, a CF array, and a patterned QD film.
We measured the optical intensity using an integrated sphere and quantum efficiency analysis system (QE-1000, Otsuka, Japan). Figure 5 shows the optical intensity spectra obtained from an LCD prepared using 1) a mixed QD film (for reference), 2) only a patterned QD film, and 3) both a patterned QD film and an SPF. Throughout the wavelength range, the optical intensity of the LCD with only a patterned QD film was higher than that of the reference. The optical intensity was further increased with the addition of an SPF. We also observed that the peak wavelengths of spectra in the red and green ranges shifted from 625 nm and 515 nm to 634 nm and 524 nm, respectively, following the formation of patterned QD films from the QD solution. We believe it is a result of self-reabsorption in the high concentration QD films.
Fig. 5 Optical intensity spectra of light from an LCD with a mixed QD film (for reference), with a patterned QD film alone, and with both a patterned QD film and an SPF.
To understand the enhancement in optical intensity of each color quantitatively, we separately measured individual RGB spectra using individual RGB CFs instead of a CF array. For the LCD with a patterned QD film and an SPF, the red and green spectra were obtained using red and green QD films and CFs each other while the blue spectrum was obtained using only a blue CF. Figures 6(a)-6(c) show the individual RGB spectra obtained from the two aforementioned LCDs. For quantitative analysis, the enhanced ratio of the optical intensities and the luminous efficacies were calculated by integrating the measured RGB spectra over the range of wavelength used, as summarized in Table 1. The optical intensities of the RGB spectra of the LCD with both a patterned QD film and an SPF were enhanced by 1.63, 1.72, and 2.16 times, respectively when compared to the values obtained from the RGB spectra of the reference LCD. The observed enhancement in the optical intensity of the blue spectrum was due to the lossless exit of the blue backlight from the LGP. In comparison, the optical intensity of the blue backlight in the reference structure decreased due to the absorption by the mixed QD film. The enhancement observed in the red and green spectra is due to two reasons: the patterned red or green QD films downconvert blue light to red or green light separately, leading to the effective transfer of light to each CF, and the SPF effectively reflected backward-emitted light from the QDs to the forward direction. The degree of enhanced green spectra was higher than that observed in the red spectra because there was less reabsorption of green light by neighboring red QDs in the case of patterned structure, where red and green QDs were separated. The luminous efficacies of the RGB spectra of the LCD with a mixed QD film were 1.95, 6.1, and 1.71 lm/W, respectively. These values changed to 2.28, 9.52, and 0.99 lm/W, respectively, for the LCD with a patterned QD film and an SPF. The luminous efficacies of the red and green spectra increased upon replacement of the mixed QD film with a patterned QD film and an SPF. However, the luminous efficacy of the blue spectrum decreased since the blue spectrum of the reference LCD included a relatively high amount of green light with high color sensitivity, as shown in Fig. 6(c). The tradeoff between luminous efficacy and the width of the color gamut is unavoidable as each reaches its maximum value at different wavelengths [27, 28]. As mentioned earlier, maximizing the latter was prioritized in this study, therefore, it is possible to further enhance luminous efficacy by changing the peak wavelengths of red and green QD films such that they are approximately equal to 550 nm, the wavelength at which the human eye is most sensitive.
Fig. 6 (a) Red, (b) green, and (c) blue spectra obtained from the LCD with a mixed QD film (solid line)) and from the LCD with both a patterned QD film and an SPF (dotted line).
Table 1. Enhanced ratio of optical intensity and luminous efficacy for an LCD prepared using a mixed QD film (for reference) and for an LCD prepared using a patterned QD film and an SPF
3.2 Color gamut
There are two definitions of color gamut based on area ratio and coverage ratio [28]. The area ratio is obtained using the RGB triangular area of a display, while the coverage ratio means only the overlapped RGB triangular area of a display with that of the standard Rec. 2020 color gamut. In this study, we basically used the color gamut based on the area ratio in CIE 1931 color space with an additional reference value of the color gamut based on the coverage ratio. As shown in Fig. 6, the full width at half maximum (FWHM) of the red and green spectra were measured as 34 and 29 nm, respectively, in case of both reference and proposed LCDs. The FWHM of the blue spectrum decreased from 21 to 18 nm upon replacement of the mixed QD film with a patterned QD film and the addition of an SPF. This was due to the transmittance characteristics of the SPF. It was also observed that the peak wavelengths of the red and green spectra were 623 and 530 nm, respectively, in case of the reference LCD, but 634 and 524 nm, respectively, in case of the proposed LCD. The peak wavelengths obtained from the LCD with patterned red and green QD films were optimized to achieve the maximum color gamut from among all available QDs. While the transmittance value of the CFs was broadly maintained to ensure greater optical intensity, the crosstalk of the RGB spectrum noticeably reduced upon use of the patterned QD film and the SPF. Consequently, as shown in Fig. 7, the color gamut increased from 89.5% of the NTSC standard in the CIE 1931 color space in case of the reference LCD with mixed QD film to 127.5% of the same in case of the LCD with the patterned QD film and the SPF, which is equivalent to 95% of the Rec. 2020 color gamut. When the color gamut was calculated based on the coverage ratio, it covered 90% of the Rec. 2020 color gamut. Enhancement of the color gamut was due to the optimized peak wavelengths of the patterned red and green QD films as well as the reduced crosstalk between the colors after passing through the CFs. The reduced crosstalk is due to the direct alignment of the QDs with the CFs. Based on experimental results, we also discovered that the SPF had a negligible effect on the enhancement of color gamut; thus, 95% of the Rec. 2020 color gamut was still realized when only a patterned QD film was used without the addition of an SPF. In addition, we showed that using simulation results, 100% of the Rec. 2020 color gamut can be obtained by using a green QD film with an FWHM of 25 nm. Based on our proposed LCD structure as well as the abundant research currently being undertaken to improve the purity of green QDs, we can reasonably expect to achieve the Rec. 2020 color gamut in the near future.
Fig. 7 Color gamut of an LCD with a mixed QD film and of an LCD with a patterned QD film and an SPF.
3.3 Internal polarizer
In our proposed LCD, the top polarizer should be placed under the patterned QD film, as the downconverted light from the red and green QDs loses the polarization property of the blue light. However, it is very difficult to insert a commercial polarizer film into the LCD as an internal top polarizer due to its thickness of around 200 µm [29]. One of the possible solutions is to use a wire-grid polarizer (WGP), formed using a regular array of parallel metallic wires, as an internal top polarizer due to its favorable properties: nanoscale thickness and high polarity in the visible region [30–34]. In this study, we used a WGP as an internal top polarizer and verified its suitability using the finite difference time domain (FDTD) simulation method. The optical properties of a WGP as a function of structural parameters were analyzed to maximize polarity in the blue region from 400 to 500 nm. This is because only blue light passes through the WGP in our proposed LCD. Figure 8 is a schematic illustration of the cross-section of the WGP used in this simulation. The structure consists of Aluminum (Al) wire-grids, that are sufficiently long along the y-direction, on a glass substrate that is embedded in a photoresist (SU-8, MicroChem). A plane wave illuminated the WGP along the positive z-direction and its boundary conditions in the x- and y-direction were obtained from a previous study [32]. The grid periods (p) from 100 to 200 nm and wire thickness (t) from 50 to 200 nm were increased in steps of 5 nm in order to observe its optical properties. Wire width (w) ranged from 20 to 80% of the grid period. To confirm the guideline for the simulation, we experimentally measured the transmittance of the TE and the TM mode, and the extinction ratio (ratio of TE transmittance to TM transmittance) from a commercial polarizer film, as shown in Fig. 9(a). In the wavelength range of 400 to 500 nm, a commercial polarizer film yielded an average TM transmittance of 70% and an average extinction ratio of 369. In the simulation, we thus focused on not only improving the performance of the WGP but also verifying the possibility of using the WGP as an internal polarizer in the LCD. Finally, we selected a WGP (p = 120 nm, w = 70 nm, and t = 80 nm) with optical properties similar to those of a commercial polarizer, as shown in Fig. 9(b). From 400 to 500 nm, the WGP resulted in an average TM transmittance of 72% and an average extinction ratio of 670. From these results, we can conclude that WGP is a potential candidate for an internal polarizer in the proposed LCD, with a performance similar to that of a commercial polarizer film. In aspect of the contrast ratio, the WGP can reduce the ambient contrast ratio by reflecting the ambient light because the WGP is a reflective-type polarizer. Thus, it may be necessary to use a circular polarizer film used in OLED display for our proposed LCD structure, although optical efficiency is decreased by absorption loss [35]. Also, an in-cell polarizer using dye or lyotropic LC would be another good candidate as an internal polarizer. In our proposed LCD structure, the patterned red and green QD film can be excited by ambient short-wavelength light, resulting in the reduced ambient contrast ratio. As discussed by Chen, H., et al., QD having separate absorption and emission spectra or color filtering material with steeper absorption edge can be a solution for the issue of ambient contrast ratio [36].
Fig. 8 Schematic illustration of the cross-section of the wire-grid polarizer used in our simulation.
Fig. 9 Transmittance of the TE and the TM mode, and the extinction ratio for (a) a commercial polarizer film (experimental results) and (b) a wire-grid polarizer (simulation results).
4. Conclusions
A new LCD structure prepared using a patterned QD film and an SPF was proposed and fabricated to enhance both optical intensity and the color gamut in comparison to conventional LCDs prepared using mixed QD films. The patterned QD film was successfully fabricated using a lithography process based on a photoresist dispersed with QDs. The SPF was designed taking into consideration the emission properties of blue LEDs and QD films. We experimentally confirmed that the optical intensities in the RGB spectrum increased by 1.63, 1.72, and 2.16 times, respectively, in the proposed LCD structure in comparison to the values obtained by a conventional LCD with a mixed QD film. The enhancement of optical intensity is a result of both the separated emission from the red and green patterned QD film as well as the reflection of red and green light to the forward direction by the SPF. The patterned QD structure also contributed to the realization of a wide color gamut by maintaining narrow bandwidth of green and red QD colors following their passage through the CFs. This was achieved by minimizing interaction between white backlight and the broad transmittance spectra of CFs such as those seen in conventional LCDs with mixed QD films. In this manner, the color gamut increased from 89.5% of the NTSC standard in the CIE 1931 color space, observed in traditional LCDs with mixed QD films, to 127.5% of the same in the proposed LCD with a patterned QD film and an SPF, which is equivalent to 95% in the area ratio and 90% in the coverage ratio of the Rec. 2020 color gamut, respectively. Based on these experimental results, we believe that an LCD prepared using a patterned QD film as a color-converting component and an SPF as an optical recycling component has strong potential for application in a highly efficient LCD display that will satisfy the Rec. 2020 color gamut requirement in the near future.
Funding
National Research Foundation of Korea (NRF) (2016R1A2B4008869); LG Display, New Mode Display (2016-11-0954).
References and links
1. ITU-R Recommendation BT.2020, “Parameter values for ultra-high definition television systems for production and international programme exchange,” 2012.
2. K. Kakinuma, “Technology of wide color gamut backlight with light-emitting diode for liquid crystal display television,” Jpn. J. Appl. Phys. 45(5B), 4330–4334 (2006). [CrossRef]
3. R. J. Xie, N. Hirosaki, and T. Takeda, “Wide color gamut backlight for liquid crystal displays using three-band phosphor-converted white light-emitting diodes,” Appl. Phys. Express 2(2), 022401 (2009). [CrossRef]
4. J. H. Oh, H. Kang, M. Ko, and Y. R. Do, “Analysis of wide color gamut of green/red bilayered freestanding phosphor film-capped white LEDs for LCD backlight,” Opt. Express 23(15), A791–A804 (2015). [CrossRef] [PubMed]
5. L. Wang, X. Wang, T. Kohsei, K. Yoshimura, M. Izumi, N. Hirosaki, and R. J. Xie, “Highly efficient narrow-band green and red phosphors enabling wider color-gamut LED backlight for more brilliant displays,” Opt. Express 23(22), 28707–28717 (2015). [CrossRef] [PubMed]
6. N. Moriya, M. Sugawara, R. Harada, T. Kageyama, and K. Matsushima, “New color filter for light-emitting diode back light,” Jpn. J. Appl. Phys. 42(1), 1637–1641 (2003). [CrossRef]
7. H. Zhan, Z. Xu, C. Tian, Y. Wang, M. Chen, W. Kim, Z. Bu, X. Shao, and S. Lee, “Achieving standard wide color gamut by tuning led backlight and color filter spectrum in LCD,” J. Soc. Inf. Disp. 22(11), 545–551 (2014). [CrossRef]
8. K. Masaoka, Y. Nishida, M. Sugawara, and E. Nakasu, “Design of primaries for a wide-gamut television colorimetry,” IEEE Trans. Broadcast 56(4), 452–457 (2010). [CrossRef]
9. K. V. Chellappan, E. Erden, and H. Urey, “Laser-based displays: a review,” Appl. Opt. 49(25), F79–F98 (2010). [CrossRef] [PubMed]
10. H. Chen, R. Zhu, G. Tan, M. C. Li, S. L. Lee, and S. T. Wu, “Enlarging the color gamut of liquid crystal displays with a functional reflective polarizer,” Opt. Express 25(1), 102–111 (2017). [CrossRef] [PubMed]
11. X. Peng, M. C. Schlamp, A. V. Kadavanich, and A. P. Alivisatos, “Epitaxial growth of highly luminescent CdSe/CdS core/shell nanocrystals with photostability and electronic accessibility,” J. Am. Chem. Soc. 119(30), 7019–7029 (1997). [CrossRef]
12. B. O. Dabbousi, J. Rodriguez-Viejo, F. V. Mikulec, J. R. Heine, H. Mattoussi, R. Ober, K. F. Jensen, and M. G. Bawendi, “(CdSe) ZnS core-shell quantum dots: synthesis and characterization of a size series of highly luminescent nanocrystallites,” J. Phys. Chem. B 101(46), 9463–9475 (1997). [CrossRef]
13. R. Xie, D. Battaglia, and X. Peng, “Colloidal InP nanocrystals as efficient emitters covering blue to near-infrared,” J. Am. Chem. Soc. 129(50), 15432–15433 (2007). [CrossRef] [PubMed]
14. S. Coe-Sullivan, “Optoelectronics: Quantum dot developments,” Nat. Photonics 3(6), 315–316 (2009). [CrossRef]
15. E. Jang, S. Jun, H. Jang, J. Lim, B. Kim, and Y. Kim, “White-light-emitting diodes with quantum dot color converters for display backlights,” Adv. Mater. 22(28), 3076–3080 (2010). [CrossRef] [PubMed]
16. S. Kim, S. H. Im, and S. W. Kim, “Performance of light-emitting-diode based on quantum dots,” Nanoscale 5(12), 5205–5214 (2013). [CrossRef] [PubMed]
17. J. H. Oh, H. Kang, M. Ko, and Y. R. Do, “Analysis of wide color gamut of green/red bilayered freestanding phosphor film-capped white LEDs for LCD backlight,” Opt. Express 23(15), A791–A804 (2015). [CrossRef] [PubMed]
18. S. Coe-Sullivan, W. Liu, P. Allen, and J. S. Steckel, “Quantum dots for LED downconversion in display applications,” ECS J. Solid State Sci. Technol. 2(2), R3026–R3030 (2013). [CrossRef]
19. J. S. Steckel, J. Ho, C. Hamilton, J. Xi, C. Breen, W. Liu, P. Allen, and S. Coe-Sullivan, “Quantum dots: The ultimate down‐conversion material for LCD displays,” J. Soc. Inf. Disp. 23(7), 294–305 (2015). [CrossRef]
20. J. Chen, V. Hardev, J. Hartlove, J. Hofler, and E. Lee, “66.1: Distinguised Paper: A high-efficiency wide-color-gamut solid-state backlight system for LCDs using quantum dot enhancement film,” Dig. Tech. Pap. 43(1), 895–896 (2012). [CrossRef]
21. Z. Luo, D. Xu, and S. T. Wu, “Emerging quantum-dots-enhanced LCDs,” J. Soc. Inf. Disp. 10(7), 526–539 (2014).
22. J. Thielen, D. Lamb, A. Lemon, J. Tibbits, J. V. Derlofske, and E. Nelson, “27-2: Invited Paper: Correlation of accelerated aging to in-device lifetime of quantum dot enhancement film,” Dig. Tech. Pap. 47(1), 336–339 (2016). [CrossRef]
23. H. J. Kim, M. H. Shin, H. G. Hong, B. S. Song, S. K. Kim, W. H. Koo, J. G. Yoon, S. Y. Yoon, and Y. J. Kim, “Enhancement of optical efficiency in white OLED display using the patterned photoresist film dispersed with quantum dot nanocrystals,” J. Disp. Technol. 12(6), 526–531 (2016). [CrossRef]
24. H. J. Kim, M. H. Shin, and Y. J. Kim, “Optical efficiency enhancement in white organic light-emitting diode display with high color gamut using patterned quantum dot film and long pass filter,” Jpn. J. Appl. Phys. 55(8), 08RF01 (2016).
25. H. M. Ng, D. Doppalapudi, E. Iliopoulos, and T. D. Moustakas, “E. lliopoulos, and T. D. Moustakas, “Distributed Bragg reflectors based on AlN/GaN multilayers,” Appl. Phys. Lett. 74(7), 1036–1038 (1999). [CrossRef]
26. R. Butté, E. Feltin, J. Dorsaz, G. Christmann, J. F. Carlin, N. Grandjean, and M. Ilegems, “Recent progress in the growth of highly reflective nitride-based distributed Bragg reflectors and their use in microcavities,” Jpn. J. Appl. Phys. 44(1010R), 7207–7216 (2005). [CrossRef]
27. Z. Luo, Y. Chen, and S. T. Wu, “Wide color gamut LCD with a quantum dot backlight,” Opt. Express 21(22), 26269–26284 (2013). [CrossRef] [PubMed]
28. R. Zhu, Z. Luo, H. Chen, Y. Dong, and S. T. Wu, “Realizing Rec. 2020 color gamut with quantum dot displays,” Opt. Express 23(18), 23680–23693 (2015). [CrossRef] [PubMed]
29. J. Ma, X. Ye, and B. Jin, “Structure and application of polarizer film for thin-film-transistor liquid crystal displays,” Displays 32(2), 49–57 (2011). [CrossRef]
30. S. W. Ahn, K. D. Lee, J. S. Kim, S. H. Kim, J. D. Park, S. H. Lee, and P. W. Yoon, “Fabrication of a 50 nm half-pitch wire grid polarizer using nanoimprint lithography,” Nanotechnology 16(9), 1874–1877 (2005). [CrossRef]
31. Y. Ekinci, H. H. Solak, C. David, and H. Sigg, “Bilayer Al wire-grids as broadband and high-performance polarizers,” Opt. Express 14(6), 2323–2334 (2006). [CrossRef] [PubMed]
32. J. J. Wang, F. Walters, X. Liu, P. Sciortino, and X. Deng, “High-performance, large area, deep ultraviolet to infrared polarizers based on 40 nm line/78 nm space nanowire grids,” Appl. Phys. Lett. 90(6), 061104 (2007). [CrossRef]
33. Z. Y. Yang and Y. F. Lu, “Broadband nanowire-grid polarizers in ultraviolet-visible-near-infrared regions,” Opt. Express 15(15), 9510–9519 (2007). [CrossRef] [PubMed]
34. G. Mélen, W. Rosenfeld, and H. Weinfurter, “Impact of the slit geometry on the performance of wire-grid polarisers,” Opt. Express 23(25), 32171–32178 (2015). [CrossRef] [PubMed]
35. B. C. Kim, Y. J. Lim, J. H. Song, J. H. Lee, K. U. Jeong, J. H. Lee, G. D. Lee, and S. H. Lee, “Wideband antireflective circular polarizer exhibiting a perfect dark state in organic light-emitting-diode display,” Opt. Express 22(S7Suppl 7), A1725–A1730 (2014). [CrossRef] [PubMed]
36. H. Chen, J. He, and S. T. Wu, “Recent advances on quantum-dot-enhanced liquid-crystal displays,” IEEE J. Sel. Top. Quantum Electron. 23(5), 1–11 (2017). [CrossRef]
