32‐1: On‐chip Red Quantum Dots in White LEDs for General Illumination

Estrada, Daniel; Shimizu, Ken D.; Böhmer, M.R.; Gangwal, Sumit; Diederich, Thomas; Grabowski, S; Tashjian, Greg; Chamberlin, D. R.; Shchekin, O.B.; Bhardwaj, Jyoti

doi:10.1002/sdtp.12585

Cited by 4 publications

(10 citation statements)

References 16 publications

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“…The California Energy Commission (CEC) standard recommends a color rendering index (CRI, the CIE R a value) of at least 90 and an R9 value of at least 50 [4], requirements we refer to as R a 90, R9 50. This recommendation matches with the general customer preferences for color fidelity [5,6]. Although the R a 90, R9 50 requirements were enacted back in 2013, their adoption by industry takes time due to the significant efficiency penalty that relates to the transition from R a 80 to R a 90 [6].…”

Section: Introductionsupporting

confidence: 54%

“…This recommendation matches with the general customer preferences for color fidelity [5,6]. Although the R a 90, R9 50 requirements were enacted back in 2013, their adoption by industry takes time due to the significant efficiency penalty that relates to the transition from R a 80 to R a 90 [6]. This penalty is mainly caused by the broad emission of the red nitride phosphors that are typically used in white LEDs.…”

Section: Introductionsupporting

confidence: 52%

“…Other advantages of QDs are their narrow and size-dependent emission spectrum, potentially high, near unity quantum efficiency, and tiny particle size in the range of a few nanometers [10,11]. Estrada et al [6] stated that with traditional inorganic phosphors as downconversion materials, the transition from R a 80 to R a 90 results in a lumen loss of 17% for a CCT of 2700 K. However, replacing red-emitting nitride phosphors with more narrowband red-emitting QDs should reduce this efficiency drop to merely 6% on a normalized lm/W basis. Such small differences are really advocating the adoption of CRI-R a 90.…”

Section: Introductionmentioning

confidence: 99%

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Efficient, high-CRI white LEDs by combining traditional phosphors with cadmium-free InP/ZnSe red quantum dots

Meuret¹,

Avermaet²,

Mingabudinova³

et al. 2021

Photon. Res.

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Quantum dots (QDs) offer an interesting alternative for traditional phosphors in on-chip light-emitting diode (LED) configurations. Earlier studies showed that the spectral efficiency of white LEDs with high color rendering index (CRI) values could be considerably improved by replacing red-emitting nitride phosphors with narrowband QDs. However, the red QDs in these studies were cadmium-based, which is a restricted element in the EU and certain other countries. The use of InP-based QDs, the most promising Cd-free alternative, is often presented as an inferior solution because of the broader linewidth of these QDs. However, while narrow emission lines are the key to display applications that require a large color gamut, the spectral efficiency penalty of this broader emission is limited for lighting applications. Here, we report efficient, high-CRI white LEDs with an on-chip color converter coating based on red InP/ZnSe QDs and traditional green/yellow powder phosphors. Using InP/ZnSe QDs with a quantum yield of nearly 80% and a full width at half-maximum of 45 nm, we demonstrate high spectral efficiency for white LEDs with very high CRI values. One of the best experimental results in terms of both luminous efficacy and color rendering performance is a white LED with an efficacy of 132 lm/W, and color rendering indices of R a ≈ 90, R9 ≈ 50 for CCT ≈ 4000 K. These experimental results are critically compared with theoretical benchmark values for white LEDs with on-chip downconversion from both phosphors and red Cd-based QDs. The various loss mechanisms in the investigated white LEDs are quantified with an accurate simulation model, and the main impediments to an even higher efficacy are identified as the blue LED wall-plug efficiency and light recycling in the LED package.

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Section: Introductionsupporting

confidence: 54%

Section: Introductionsupporting

confidence: 52%

Section: Introductionmentioning

confidence: 99%

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Efficient, high-CRI white LEDs by combining traditional phosphors with cadmium-free InP/ZnSe red quantum dots

Meuret¹,

Avermaet²,

Mingabudinova³

et al. 2021

Photon. Res.

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show abstract

“…In addition to the thermal drift of the emission color, the stability and chemical integrity of CdSe NPs at the operating temperature in w-LEDs for on-chip application of QDs are a concern. Recently, coating strategies have been developed that allow for on-chip application in midpower LEDs ,, and give hope that the stability of CdSe NPLs can be improved in a similar way to enable on-chip application in w-LEDs.…”

Section: Resultsmentioning

confidence: 99%

“…Hence, there is a need for narrow band red emitters. This can be achieved by using semiconductor nanoparticles (NPs) such as CdSe or InP quantum dots (QDs). , The success of these NPs has already been demonstrated in the quantum dot light emitting diode (QLED) displays of Samsung . The use of both a narrow band green and red emitter increases the efficiency and widens the color gamut of these displays significantly.…”

Section: Introductionmentioning

confidence: 99%

Luminescence Line Broadening of CdSe Nanoplatelets and Quantum Dots for Application in w-LEDs

et al. 2020

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Nanoplatelets (NPLs) of CdSe are an emerging class of luminescent materials, combining tunable and narrow emission bands with high quantum yields. This is promising for application in white light LEDs (w-LEDs) and displays. The origin of the narrow spectral width of exciton emission in core NPL compared to core–shell NPL and quantum dot (QD) emission is not fully understood. Here we investigate and compare temperature-dependent emission spectra of core and core–shell CdSe NPLs and QDs. A wide temperature range, 4–423 K, is chosen to gain insight into contributions from homogeneous and inhomogeneous broadening and also to extend measurements into a temperature regime that is relevant for operating conditions in w-LEDs (T ≈ 423 K). The results show that temperature-induced homogeneous broadening does not strongly vary between the various CdSe nanostructures (ΔE hom ≈ 60–80 meV at 423 K) indicating that electron–phonon coupling strengths are similar. Only for the smallest QDs is stronger coupling observed. The origin of the narrow bandwidth reported at 300 K for core CdSe NPLs is attributed to a very narrow inhomogeneous line width. At 423 K, the spectral width of NPL exciton emission is still narrower than that of QDs. A comparison with traditional w-LED phosphors is made to outline advantages (tunability, narrow bandwidth, high efficiency) and disadvantages (color shift, stability issues) of NPLs for application in w-LEDs.

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In Situ Optical and X-ray Spectroscopy Reveals Evolution toward Mature CdSe Nanoplatelets by Synergetic Action of Myristate and Acetate Ligands

et al. 2022

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The growth of two-dimensional platelets of the CdX family (X = S, Se, or Te) in an organic solvent requires the presence of both long- and short-chain ligands. This results in nanoplatelets of atomically precise thickness and long-chain ligand-stabilized Cd top and bottom surfaces. The platelets show a bright and spectrally pure luminescence. Despite the enormous interest in CdX platelets for optoelectronics, the growth mechanism is not fully understood. Riedinger et al. studied the reaction without a solvent and showed the favorable role for short-chain carboxylates for growth in two dimensions. Their model, based on the total energy of island nucleation, shows favored side facet growth versus growth on the top and bottom surfaces. However, several aspects of the synthesis under realistic conditions are not yet understood: Why are both short- and long-chain ligands required to obtain platelets? Why does the synthesis result in both isotropic nanocrystals and platelets? At which stage of the reaction is there bifurcation between isotropic and 2D growth? Here, we report an in situ study of the CdSe nanoplatelet reaction under practical synthesis conditions. We show that without short-chain ligands, both isotropic and mini-nanoplatelets form in the early stage of the process. However, most remaining precursors are consumed in isotropic growth. Addition of acetate induces a dramatic shift toward nearly exclusive 2D growth of already existing mini-nanoplatelets. Hence, although myristate stabilizes mini-nanoplatelets, mature nanoplatelets only grow by a subtle interplay between myristate and acetate, the latter catalyzes fast lateral growth of the side facets of the mini-nanoplatelets.

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32‐1: On‐chip Red Quantum Dots in White LEDs for General Illumination

Cited by 4 publications

References 16 publications

Efficient, high-CRI white LEDs by combining traditional phosphors with cadmium-free InP/ZnSe red quantum dots

Efficient, high-CRI white LEDs by combining traditional phosphors with cadmium-free InP/ZnSe red quantum dots

Luminescence Line Broadening of CdSe Nanoplatelets and Quantum Dots for Application in w-LEDs

In Situ Optical and X-ray Spectroscopy Reveals Evolution toward Mature CdSe Nanoplatelets by Synergetic Action of Myristate and Acetate Ligands

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