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Abstract
II−VI colloidal semiconductor nanoplatelets (NPLs) are a kind of two-dimensional nanomaterial with uniform thickness at the atomic scale, thus leading to the characteristics of tunable emission wavelength and narrow bandwidth. Here, we report wide color gamut white light-emitting diodes (WLEDs) based on high-performance CdSe-based heterostructure NPLs. The narrow-band CdSe/CdS core/crown and CdSe/ZnCdS core/shell NPLs are chosen as green (∼521 nm) and red (∼653 nm) luminescent materials, respectively. They represent excellent PL properties, such as narrow linewidth, high quantum yields, and high photostability. Importantly, the further fabricated NPL-WLEDs exhibits an ultrawide color gamut covering up ∼141.7% of the NTSC standard in the CIE 1931 color space and excellent stability towards driving currents. These outstanding device performances indicate that the colloidal semiconductor NPLs possess huge potentiality to achieve higher color saturation and wide color gamut for applications in new-generation lightings and displays.
© 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
Two-dimensional (2D) II−VI colloidal semiconductor nanoplatelets (NPLs) have obtained great attention due to their flat thickness confined at the atomic scale [1,2]. The distinctive optical features of NPLs present the precisely monolayer (ML) thickness dependent band-edge energy level, ultranarrow emission spectra (linewidth of ∼8-10 nm), and high photoluminescence quantum yield (PL QY) [3–5]. The extremely narrow emission linewidth is highly applicable for improving color purity and achieving wide color gamut display [6,7]. Therefore, NPLs-based white light-emitting diodes (WLEDs) are highly promising for applications in solid-state lightings and displays.
Over the last decade, narrow-band emitters have been recognized as key factors for wide color gamut LEDs backlights in liquid-crystal displays (LCD) [6–9]. Today, semiconductor quantum dots (QDs) have exhibited the practical application values in either photoluminescent or electroluminescent (EL) LEDs and successfully towards commercial applications as television display backlights due to their excellent optical properties [7,10–16]. The narrow-band green/red luminescent QDs in white QD-LEDs are superior in high color saturation compared to the traditional phosphors LEDs, proving the superiority to expand the color gamut [6–11]. However, the narrowest PL spectra of either CdSe-, CuInS- or perovskite-based semiconductor QDs are difficult to less than ∼20 nm in ensemble, due to their strong three-dimensional quantum confined effect leading to broaden the emission spectra [6,7,17–19]. To further improve the WLEDs device performance on the basis of QDs display technologies, 2D NPLs precisely present a good opportunity for high color gamut backlighting display of LEDs, because of their ultranarrow emission spectra. In recent years, many research groups devote to explore the growth mechanism of a series of CdSe NPLs with different thickness (2 ML to 9 ML) by controlling the colloidal synthesis scheme [20–22]. On the other hands, Sargent group achieved the continuous tunable emission wavelength of narrow-band CdSe1-xSx NPLs by controlling the injection ratio of selenium and sulfur precursors, and its EL LED device created the narrowest emission full-width-half-maximum (FWHM) record (∼12.5 nm) of colloidal nanomaterials at 520 nm [23]. Therefore, the emission wavelength of CdSe-based NPLs could cover most visible light areas with the continuous adjustment in reality and no longer the constraint of thickness dependence, which was beneficial to optimize the display performance of WLEDs according to practical requirements. In addition to purer color emission, the NPLs still have the advantages of optical properties and device fabrication like as QDs, including high quantum efficiency, tunable emission spectra, and facile solution processability [3–5,20–23]. Particularly, CdSe-based NPLs heterostructures have been synthesized and widely investigated, such as core/shell, core/crown, and core/crown/shell NPLs [24–30]. These heterostructures NPLs have been proven not only efficiently improve PL QYs (above ∼90%), it could also be obviously enhanced optical thermal and UV stability, while maintaining narrow emission FWHM (green emission NPLs: ∼10 nm; red emission NPLs: ∼20 nm) [27,29–32]. Besides, core/crown NPLs showed the potential values in ultragreen LED and white LED device, which would extremely enhance the color gamut of white emitting device [33–36]. Notably, luminescence materials must have high emission efficiency, high color purity, and operational stability to provide satisfactory display quality [7]. Because of above advantages, heterostructure NPLs present more promising in the WLED display applications with a wide color gamut, high brightness, and excellent photostability, which are expected to realize better device performance than QD-LEDs. Furthermore, although white emission from semiconductor NPLs is desirable for high-quality displays, the NPL-WLEDs device has not been explored that totally based on green and red emitting NPLs yet to date. Therefore, it is meaningful to promote the further development of display backlights by studying white emitting NPL-LEDs.
In this work, we fabricate an efficient wide-color gamut WLEDs by integrating narrow-band green/red emissive CdSe/CdS core/crown (∼521 nm) and CdSe/ZnCdS core/shell (∼653 nm) NPLs composite matrix onto the blue LED chip for the first time. The synthesized green emitting CdSe/CdS core/crown NPLs have a PL QY up to ∼80% with a narrow FWHM of ∼10 nm. The red emitting CdSe/ZnCdS core/shell NPLs could realize the narrower FWHM of ∼23 nm that near the limitation of conventional QDs, as well as high PL QY of ∼91%. Particularly, these heterostructure NPLs show the enhanced photostability under ultraviolet radiation compared to CdSe core NPLs, as well as the excellent optical thermal stability embedded in polymeric matrix. Finally, the obtained NPL-WLEDs exhibit high-performance white emitting with an NTSC value of ∼141.7% and Rec. 2020 of ∼105.8% due to the narrow emission wavelength of the NPLs. Our results clearly demonstrate the potential of 2D semiconductor NPLs for ultrawide color gamut backlighting display of LEDs applications.
2. Experimental section
2.1 Synthesis of CdSe-based heterostructure NPLs
Synthesis of CdSe core NPLs: The CdSe core NPLs (4 MLs) was synthesized by a previous reported method [26]. The purified core NPLs was dissolved in hexane for the following use.
Synthesis of CdSe/CdS core/crown NPLs: The synthesis of CdSe/CdS core/crown NPLs was performed with the injection of the mixed cadmium and sulfur precursors, which was prepared in advance according to the previous reported method [32]. For a typical synthesis, a half of CdSe core NPLs (4 MLs) that was dissolved in hexane, 100 µL of oleic acid (OA), and 5 mL of 1-octadecene (ODE) was loaded into a 50 mL three-neck flask with a magnetic stirrer. The solution was degassed at 80°C for 30 min to remove all hexane, water, and oxygen inside the solution. Then, under the inert atmosphere, the solution was heated to 240°C. When temperature reached 240°C, the cadmium and sulfur mixture precursors was injected with the rate of 8 mL/h using a syringe pump. The injection amount could be changed according to desired CdS crown size. After the injection of precursors, the reaction was stopped with the injection of 0.5 mL of OA and the system was cooled to room temperature. The CdSe/CdS core/crown NPLs were purified 1-2 times with ethanol. Finally, the precipitated NPLs were dissolved in chloroform.
Synthesis of CdSe/ZnCdS core/shell NPLs: CdSe/ZnCdS core/shell NPLs was synthesized according to a method from the Ref. [30]. A mixture of 11.53 mg of Cd(acetate)2, 27.52 mg of Zn(acetate)2, 0.5 mL of OA, CdSe core NPLs (4 MLs) in hexane, and 5 mL ODE was added into a 50 mL three-neck flask. The flask was degassed at room temperature for 80 min together with a magnetic stirrer. Then the temperature of the mixture was increased up to 300°C to form Cd and Zn precursors. 0.5 mL of oleylamine was injected at 90°C. 70 µL of 1-octanethiol in 4 mL of ODE was used as the sulfur precursor, and then injected at 165°C with the rate of 10 mL/h by a syringe pump. Next, the injection rate was decreased to 4 mL/h when the temperature of the solution reached 240°C. When the temperature reached 300°C, the solution was kept at this temperature for 40 min. Then the reaction was stopped to room temperature and 5 mL of hexane was added. The synthesized CdSe/ZnCdS core/shell NPLs were purified 1-2 times with ethanol, and the precipitated NPLs were redispersed in hexane or chloroform.
2.2 Measurement and characterization
Transmission electron microscopy (TEM) images were obtained on a JEM-2100 electron microscope. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images were obtained on a FEI Talos F200X electron microscope. The absorption spectra were measured on a UV-vis-NIR spectrophotometer (Shimadzu UV3600). The PL spectra were recorded using a spectrofluorometer (Shimadzu RF-5301PC), PL decay traces were monitored at the PL peak wavelength. The PL QY of the NPLs was measured relative to a standard dye (Rhodamine B (QY, 50%)) at an identical optical density. For the photostability measurement, the NPLs solutions were placed under a UV lamp (365 nm, 6 W) and the NPLs polymer films were put onto a heating platform at different temperatures under inert gas atmosphere for 10 min, and then PL spectra of the treated NPL solutions and films were recorded by a spectrofluorometer (Shimadzu RF-5301PC). For NPL-WLEDs fabrication, the red and green emitting NPLs solution was mixed with 1 mL of chloroform solution of PMMA (20% mass fraction), respectively. The red and green NPL mixture with the suitable ratio was stirred for 10 min, which was adjusted based on the measurement results of their color coordinates and emission performance. Then, the mixed green/red-emitting NPL-polymer composites were deposited into a lens hood of a blue LED chip. The commercial blue LED chip was purchased from Shenzhen looking long technology co., LTD and emitting at ∼449 nm. When the solvent of composites evaporates completely, the lens hood was fixed onto a blue LED chip for the following device performance test. For NPL-WLEDs EL measurement, a direct current stabilized voltage source (GWINSTEK GPS-2303C) was used to apply the driven current for WLEDs. The emission spectra of device were measured by an Ocean optics STS-VIS luminescence spectrometer at room temperature under different driving current and different operation time (light intensity of blue LED, ∼51 mW cm−2); the luminous efficiency of device was obtained on a spectral illuminance analyzer (OHSP-350) at driving current of 20 mA. For NPL-WLEDs performance measurement, the color gamut performance parameters of WLEDs device were calculated by CIE Chromaticity Coordinate Calculation software and Color Calculator software based on EL spectra and color coordinates.
3. Results and discussion
3.1 Structural and optical characterization
In this report, we propose the high-performance WLEDs with wide color gamut can be achieved by narrow-band emitting, superior color purity, and high emission efficiency of the semiconductor CdSe-based NPLs heterostructure as color emission materials. Among them, CdSe/CdS core/crown NPLs only grown the CdS layer around the edge of core NPLs and passivate on the lateral direction, ensuring a high PL QY and nonshifted emission wavelength [24,32–36]. Furthermore, CdSe core NPLs with 4 monolayers (4 MLs, emission peak of ∼515 nm) has narrow emission band ranging from 500 nm to 530 nm, which was right at the green color area of chromaticity diagram, thus CdSe/CdS core/crown NPLs (4 MLs) was a potential candidate material for ultrapure green color and wide color gamut display [6,7]. Currently, it hard to directly synthesized high-performance red emitting CdSe/CdS core/crown NPLs, because the synthesis of narrow-band (∼10 nm) red-emitting CdSe core NPLs with high quantum efficiency remained challenges [21,22]. On the other hand, CdSe-based core/alloyed shell NPLs could easily realize high-performance deep-red emission (high QY > 90%, narrower FWHM of ∼20 nm, and enhanced stability), which have been successfully explored in application of EL LED and laser device [29,30]. Therefore, CdSe/ZnCdS core/shell NPLs was here chosen as red-emitting material. The best-performance green/red emissive CdSe/CdS core/crown and CdSe/ZnCdS (Zn0.75Cd0.25S) core/shell NPLs with the optimized crown and shell were synthesized according to the relevant references, which was on the basis of CdSe NPLs (4 MLs) by conventional two-step process [30,32].
As shown in Fig. 1(a), the PL spectra of CdSe core and CdSe/CdS core/crown are located at ∼515 nm and ∼518 nm, respectively. The FWHM of emission peak in CdSe/CdS core/crown NPLs was about ∼10 nm for pure green color and without obvious broadening, because of the maintained strong one-dimensional quantum confinement effect in thickness direction for core/crown NPLs. The PL QY of core/crown NPLs was raised from ∼25% of core NPLs to ∼80%, which may result from the enhanced passivation effect and radiative efficiency by CdS crown [24]. The emission peak of CdSe/ZnCdS core/shell NPLs was redshifted from ∼515 nm to ∼647 nm due to the reduced quantum confined effect with shell deposition, which was attributed to electron delocalization into the shells in a quasi-type II structure [29,30]. The FWHM of the CdSe/ZnCdS core/shell NPL was broaden to ∼23 nm in comparison to CdSe core and with high QY up to ∼91%. However, the FWHM of CdSe/ZnCdS NPLs was still comparable to that of best values in conventional semiconductor QDs (∼20 nm) [6]. Fig. 1(b) shows the absorption spectra of CdSe core, CdSe/CdS core/crown, and CdSe/ZnCdS core/shell NPLs. There are typical absorption features for different heterostructure NPLs, such as almost no-shifted emission peaks and new absorption peak at 408 nm for core/crown NPLs, and the obvious redshift and broadening of two absorption peaks for core/shell NPLs. Furthermore, CdSe/CdS core/crown NPLs presented the similar PL lifetime as core NPLs resulted from the strong quantum confinement effect inner CdSe core, with a slight increase from core of 4.5 ns to 6.6 ns (Fig. 1(c)) [37]. It is in sharp contrast to that in CdSe/ZnCdS core/shell NPLs, which showed their PL lifetime largely increased to ∼23.1 ns because of the diffuse of electrons into the shells and thus a reduction of the overlap between excitons (Fig. 1(d)) [38].
Fig. 1. (a) PL spectra of CdSe core, CdSe/CdS core/crown, and CdSe/ZnCdS core/shell NPLs, inset: photographs of CdSe/CdS core/crown NPLs (left) and CdSe/ZnCdS core/shell NPLs (right) in solution under UV light irradiation. (b) Absorption spectra of CdSe core, CdSe/CdS core/crown, and CdSe/ZnCdS core/shell NPLs. (c) PL decay traces of CdSe core and CdSe/CdS core/crown NPLs. (d) PL decay traces of CdSe core and CdSe/ZnCdS core/shell NPLs.
Besides, the morphology of the core, core/crown, and core/shell NPLs was observed by TEM images shown in Fig. 2(a)-(c). The obtained CdSe/CdS core/crown NPLs feature a larger lateral length and width (40.35 nm and 29.56 nm) compared to the CdSe NPLs (27.36 nm and 12.88 nm), indicating the successful growth of CdS crown around the lateral of CdSe core NPLs (Fig. 2(a),(b)). At the same time, the average length and width of core/shell NPLs are 29.49 nm and 13.94 nm, which was approximately consistent to that of CdSe NPLs (Fig. 2(a),(c)). The average thickness of CdSe/ZnCdS NPLs estimated to be of ∼5 nm, thus confirming the formation of ZnCdS shells with thickness of ∼6 MLs, as shown in insert of Fig. 2(c). Moreover, the analyses of HAADF-STEM and elemental mapping images of these samples (Fig. 2(d)-(g)), further exhibit the characteristics of CdS crown and ZnCdS shell on CdSe core NPLs, respectively. Therefore, the above results demonstrated that these NPLs were successfully synthesized and possessed excellent optical properties with narrow FWHM and high PL QYs for the new-generation lighting and display applications.
Fig. 2. TEM images of (a) CdSe core, (b) CdSe/CdS core/crown, and (c) CdSe/ZnCdS core/shell NPLs, inset in (c): the morphology of core/shell NPLs in vertical direction with an average thickness of ∼5 nm. (d-g) HAADF-STEM and elemental mapping images of core/crown and core/shell NPLs, respectively. Scale bar are 50 nm.
3.2 Optical stability
The photostability of colloidal semiconductor nanomaterials is a great challenge for their application in lighting display technology. Because long-term light illumination could induce the PL quenching and degradation of optical performance in colloidal nanomaterials [6,7]. Therefore, we explored the photostability of CdSe only, CdSe/CdS core/crown, and CdSe/ZnCdS core/shell NPLs in solution under continuous UV irradiation (365 nm, 6 W). Figure 3(a) shows the evolution of PL intensity of the CdSe core, CdSe/CdS core/crown, and CdSe/ZnCdS core/shell NPLs along with the UV irradiation time, as well as corresponding photographs at different stages. The CdSe core NPLs reveals a large drop of ∼60% after 12 h of UV irradiation and finally decreased to below ∼13% of the initial intensity, which was related to the irradiation-induced traps on the surface of naked core and without any effective surface protection. For CdSe/CdS core/crown NPLs, their photostability was obviously enhanced upon the formation of CdS crown, which ultimately kept ∼62% of their initial intensity. CdSe/ZnCdS core/shell NPLs still showed bright red fluorescence after continuous irradiation for 216 h (insert in Fig. 3(a)). The PL emission of CdSe/ZnCdS core/shell NPLs was quite stable and exhibits remnant PL intensity near ∼90%. Noticeably, CdSe/CdS core/crown NPLs shows a lower stability than CdSe/ZnCdS core/shell NPLs, because of the CdS crown just playing roles on their lateral direction and lack of enough surface passivation. As a whole, due to the efficient protection effect provided by CdS crowns and ZnCdS shells, the CdSe/CdS core/crown and CdSe/ZnCdS core/shell NPLs show dramatically enhanced photostability under continuous UV irradiation compared to CdSe core only NPLs.
Fig. 3. (a) The remnant PL intensity of CdSe core, CdSe/CdS core/crown, and CdSe/ZnCdS core/shell NPLs in solution along with UV light irradiation time, inset: photographs of the samples at different stages. (b) PL spectra of CdSe/CdS core/crown and (c) CdSe/ZnCdS core/shell NPLs film under different temperature treatment.
On the other hand, the thermal effect of photoelectric device will also damage the optical performances of the NPLs [39]. In the practical application of photoelectric device, the active luminescent materials should be embedded in the polymeric matrix to improve device operation stability [6,7,10,36]. Considering the application of above NPLs as color emitters in LEDs device, the colloidal NPLs are further encapsulated into polymethyl methacrylate (PMMA) polymer. Their emission efficiency slightly decreased to ∼65% and ∼82% for CdSe/CdS core/crown and CdSe/ZnCdS core/shell NPLs in their polymer film, respectively. The decreased emission efficiency was mainly caused by the re-absorption effect in NPLs film due to higher concentration [10,35]. Compared to the PL spectra of green/red emitting NPLs in solution, their emission peak was redshifted by 3 nm and 6 nm, and their FWHM also broadened 2 nm and 4 nm, respectively. At the same time, the thermal stability of CdSe-based NPL-PMMA composite films was further investigated by continuous heating at different temperatures. Figure 3(b),(c) display the PL spectra of the CdSe/CdS core/crown and CdSe/ZnCdS core/shell NPLs film with the heating temperature, respectively. After the same heating treatment at ambient condition, the remnant PL intensities of CdSe/CdS core/crown and CdSe/ZnCdS core/shell NPLs still maintained ∼82% and ∼94% of their initial intensities, indicating that these CdSe-based NPLs were very promising candidates in LED applications since the operating temperature as high as 120°C. Overall, CdSe/ZnCdS core/shell NPLs showed a better optical thermal stability then CdSe/CdS core/crown NPLs, which further cleared that the alloyed ZnCdS shells could further significantly improve photostability of NPLs due to their provided efficient passivation for surface defects. Moreover, no obvious spectra shifts and broadening were observed with the increasing temperature. Therefore, CdSe/CdS core/crown and CdSe/ZnCdS core/shell NPLs composite emitters exhibit the excellent photostability against thermal environment for further lighting display WLEDs.
3.3 Wide-color-gamut WLEDs application based on NPLs
To further explore the potential values of NPLs in display fields, all NPLs white-emitting LEDs were here constructed by combining green/red-emitting CdSe/CdS core/crown and CdSe/ZnCdS core/shell NPLs embedded in polymer matrix with a blue LED chip (wavelength: ∼449 nm). Figure 4(a) gives the schematic of the NPL-WLEDs device, the mixed NPLs-PMMA composites was deposited into lens hood of a blue LED chip. The noncontact excitation could contribute to reduce the degradation of optical properties of NPLs emitters resulted from the thermal effect of blue chip, thus benefiting the device operation stability [7,39]. Fig. 4(b) exhibits the emission spectra of blue LED chip, CdSe/CdS core/crown NPL-LED, and CdSe/ZnCdS core/shell NPL-LED. Their three different emission peaks located at ∼449 nm, ∼521 nm, and ∼653 nm, respectively. Notably, the narrow-band emission spectra of green/red emitting NPL-LEDs were almost comparable to that in film, indicating the superior color purity (see the insert photographs). Figure 4(c) displays the EL spectrum of as-fabricated NPL-WLED at a driving current of 10 mA. The inset showed a photograph of the device in operation and observed the bright natural white light emission. Among, the luminous efficiency of ∼65 lm W−1 was achieved from this WLED. The color coordinates of NPL-WLED could reached (0.31, 0.32) in CIE 1931 chromaticity diagram (Fig. 4(d)), which closed to the natural white point (0.33, 0.33), indicating good white emission performance of the NPL-WLED. Meanwhile, the color coordinates of red/green/blue emission spectra is located at (0.71, 0.29), (0.10, 0.80), and (0.15, 0.02), respectively. Owing to the saturated color CIE (0.71, 0.29) and (0.10, 0.80) of red/green NPL emission, NPL-WLED was further approached to purer red and green color compared to that in NTSC standard and Rec. 2020 standard (Fig. 4(d)). Therefore, the color gamut of the NPL-WLED covered ∼105.8% of the Rec. 2020 standard in the CIE 1931 color space. For the NTSC standard, the color gamut was as high as ∼141.7% in the CIE 1931 color space, which was near 2 times that of a traditional phosphor backlight (∼72%). At the same time, such wide color gamut performance was also obviously superior to that of the previous reported semiconductor CdSe-based QDs and perovskites WLEDs [6,7]. This result was attributed to the narrow emission linewidth of the semiconductor red/green NPLs. In addition, the NPL-WLED presented the remarkable color rendering performance (left) in comparison to common white backlights (right), as demonstrated in Fig. 4(e).
Fig. 4. (a) Schematic diagram of the WLEDs device fabricated by mixing green-emitting CdSe/CdS core/crown NPLs and red-emitting CdSe/ZnCdS core/shell NPLs on a blue-LED chip. (b) The emission spectra of blue LED, CdSe/CdS core/crown NPL-LED, and CdSe/ZnCdS core/shell NPL-LED, inset: photographs of the red/green/blue LED in operation. (c) The emission spectrum of NPL-WLED, inset: photograph of WLED in operation. (d) The color coordinates of NPL-WLED in the Commission Internationale de I’Eclairage (CIE) 1931 chromaticity diagram, and their color gamut compared to the NTSC (National Television System Committee) standard and the Rec. 2020 (International Telecommunication Union Recommendation BT 2020) standard. (e) Color rendering performance of as-fabricated NPL-WLED (left) and normal backlight (right) for different colors.
In order to evaluate the NPL-WLEDs operation stability, the emission spectra of this NPL-WLED with different driving currents and different operation time were detected. With increasing driving currents, the measured spectral shape and peak position of WLED was no evident change (Fig. 5(a)). Besides, the insert given the color coordinates of WLED at different driving current. The corresponding coordinates were mainly located within the white light area, indicating their white emission performance with good current-driven stability. At the same time, the EL spectra were measured to assess the stability of WLED device as a function of operation time at operating current of 10 mA. After operating for continuous 24 h, no obvious spectral variation or shift was observed in the emission spectra (Fig. 5(b)); the emission intensity of green and red NPLs could be maintained above ∼80% and ∼92% of their initial intensity, revealing that the constructed NPLs based WLEDs possess good stability for practical applications. Our results clearly demonstrate their great potential of 2D semiconductor NPLs as high-performance green/red-emitting materials in WLEDs towards wide color gamut display backlights.
Fig. 5. (a) Intensity spectra of the constructed NPL-WLED operated at different driving currents ranging from 5 to 80 mA, inset: the corresponding color coordinates of WLED under different driving currents. (b) EL spectra of WLED as a function of operation time.
4. Conclusion
In summary, this work highlights the future prospects of using all-NPLs WLEDs with desired ultrawide color gamut for next-generation display backlights. We explore the narrow-band green/red luminescent 2D CdSe-based NPLs with high quantum efficiency and excellent stability as the pure color emitters to further promote the display performance of WLEDs. The high-performance NPL-WLEDs present an efficient wide color gamut upto ∼141.7% of NTSC and ∼105.8% of Rec. 2020 standards, which presents advantages compared to that of traditional phosphor backlight and QDs-based WLEDs, revealing their potentiality dominates for lighting and display areas. However, several challenges still remain for NPL-WLED lightings or displays. Till now, the synthesis of narrow-band (∼10 nm) red-emitting CdSe core and corresponding core/crown heterostructure NPLs with high quantum efficiency need more explorations and efforts in this direction. Besides, the photostability of core/crown NPLs should be further studied by effective surface passivation or device encapsulation to stand the strict tests in practical optoelectronics device. Therefore, it is important for the development of high-quality NPLs luminescent materials to satisfy the realistic requirements, and contribute to current and future lighting and display solutions.
Funding
National Natural Science Foundation of China (12004201); Innovation and Entrepreneurship Program of Jiangsu Province (JSSCBS20211137).
Disclosures
The authors declare no conflicts of interest.
Data Availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
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