More Like this

1. Green syntheses of stable and efficient organic dyes for organic hybrid light-emitting diodes

   https://doi.org/10.1039/D1TC01567B  

   Huang, Yunping ; Cohen, Theodore A. ; Sommerville, Parker J. ; Luscombe, Christine K. ( January 2021 , Journal of Materials Chemistry C)

   null (Ed.)

   Organic hybrid light-emitting diodes (hybrid-LEDs) employ organic dyes as light converters on top of commercial blue inorganic LEDs, replacing incumbent inorganic phosphor light converters synthesized from rare-earth and/or toxic metallic elements to optimize device environmental sustainability. Here, we present two naturally derived organic dyes for hybrid-LEDs, highlighting stability and efficiency enhancement based on a novel “acceptor–acceptor” molecular design. This “acceptor–acceptor” skeleton comprises theobromine and thiadiazole, two electron-withdrawing groups that lower energy levels and suppress photooxidation. This differentiates these dyes from the widely adopted “donor–acceptor” skeleton, where photooxidation is facilitated by the presence of electron-donating units. Simultaneously, sidechains on organic dyes used to enhance solution processability, crucial for film transparency, introduce an additional photooxidation pathway. With this “acceptor–acceptor” skeleton, the destabilization from sidechains was offset by the stability enhancement from the electronic effects in the backbone. When blended within an industrial polymer, poly(styrene-butadiene-styrene) (SBS), their enhanced solubility enables the formation of highly transparent films, crucial for reducing scattering loss in LEDs. Furthermore, resultant dye-SBS films achieved photoluminescence quantum yields (PLQYs) of around 90% under ambient conditions. Taking advantage of their transparency and solution processability, we fabricated a waveguide with this theobromine-dye-SBS composite, which was subsequentially assembled into an edge-lit LED device of no glare and enhanced aesthetics. 

   more » « less
2. Advancing Human-Centric LED Lighting Using Na2MgPO4F:Eu2+

   https://doi.org/10.1021/acsami.1c00909  

   Hariyani, Shruti ; Brgoch, Jakoah ( March 2021 , ACS Applied Materials & Interfaces)

   null (Ed.)

   The proliferation of energy-efficient light-emitting diode (LED) lighting has resulted in continued exposure to blue light, which has been linked to cataract formation, circadian disruption, and mood disorders. Blue light can be readily minimized in pursuit of “human-centric” lighting using a violet LED chip (λem ≈ 405 nm) downconverted by red, green, and blue-emitting phosphors. However, few phosphors efficiently convert violet light to blue light. This work reports a new phosphor that meets this demand. Na2MgPO4F:Eu2+ can be excited by a violet LED yielding an efficient, bright blue emission. The material also shows zero thermal quenching and has outstanding chromatic stability. The chemical robustness of the phosphor was also confirmed through prolonged exposure to water and high temperatures. A prototype device using a 405 nm LED, Na2MgPO4F:Eu2+, and a green and red-emitting phosphor produces a warm white light with a higher color rendering index than a commercially purchased LED light bulb while significantly reducing the blue component. These results demonstrate the capability of Na2MgPO4F:Eu2+ as a next-generation phosphor capable of advancing human-centric lighting. 

   more » « less
3. Dual-site occupancy induced broadband cyan emission in Ba 2 CaB 2 Si 4 O 14 :Ce 3+

   https://doi.org/10.1039/D0TC02625E  

   You, Shihai ; Zhuo, Ya ; Chen, Qiulin ; Brgoch, Jakoah ; Xie, Rong-Jun ( November 2020 , Journal of Materials Chemistry C)

   null (Ed.)

   There is a significant need to identify cyan-emitting phosphors capable of filling the “cyan-gap” (480–520 nm) in full-visible-spectrum phosphor-converted white light-emitting diodes (pc-wLEDs). Here, a new broadband cyan-emitting phosphor that enables addressing of this challenge is reported. The compound, Ba 2 CaB 2 Si 4 O 14 :Ce 3+ , presents a bright cyan emission peaking at 478 nm with a large full width at half maximum of 142 nm (6053 cm −1 ), and minimal thermal quenching. The photoluminescence properties originate from Ce 3+ residing at two different crystallographic sites, a [BaO 9 ] distorted elongated square pyramid and a [CaO 6 ] trigonal prism. This combination results in an efficient, broad emission covering the blue to green region of the visible spectrum. Fabricating a simple dichromatic ultraviolet ( λ ex = 370 nm) pumped pc-wLED using Ba 2 CaB 2 Si 4 O 14 :Ce 3+ along with a commercially available red phosphor demonstrates full-visible-spectrum white light with high color rendering index ( R a > 90) and tunable correlated color temperature, showing the potential of this material for achieving high-quality LED-based lighting. 

   more » « less
4. Rare-earth single atom based luminescent composite nanomaterials: Tunable full-color single phosphor and applications in WLEDs

   https://doi.org/10.1007/s12274-021-3886-x  

   Bao, Shan ; Yu, Haiyue ; Gao, Guoyang ; Zhu, Hongyang ; Wang, Dingsheng ; Zhu, Peifen ; Wang, Guofeng ( October 2021 , Nano Research)

   High-quality single-component white phosphors are instrumental in realizing high-efficiency devices. Rare earth fluorides and carbon quantum dots have great potential in the white light-emitting diode (WLED) field due to their unique advantages. Here, Rare-earth single atom based NaGdF4:Tb3+/Eu3+@C:N/Eu3+ single phosphor with tunable full-color luminescence was reported. The results of density functional theory (DFT) calculation and experimental characterization show that C atoms cannot be replaced by Eu3+, but C atoms are more favorable for anchoring Eu3+ single atoms. The DFT was employed to optimize the structures of the C:N/Eu3+ and NaGdF4:Tb3+/Eu3+, and calculate the work function, optical properties, and charge density difference. The obtained tunable full-color single phosphor can emit stable light from blue to red or even white. The constructed WLED devices also have stable and excellent color performance, that is, a color rendering index of up to 95 and a lower color temperature, and it has broad application possibilities in WLEDs. 

   more » « less
5. Highly Efficient Spectrally Stable Red Perovskite Light‐Emitting Diodes

   https://doi.org/10.1002/adma.201707093  

   Tian, Yu ; Zhou, Chenkun ; Worku, Michael ; Wang, Xi ; Ling, Yichuan ; Gao, Hanwei ; Zhou, Yan ; Miao, Yu ; Guan, Jingjiao ; Ma, Biwu ( March 2018 , Advanced Materials)

   Perovskite light‐emitting diodes (LEDs) have recently attracted great research interest for their narrow emissions and solution processability. Remarkable progress has been achieved in green perovskite LEDs in recent years, but not blue or red ones. Here, highly efficient and spectrally stable red perovskite LEDs with quasi‐2D perovskite/poly(ethylene oxide) (PEO) composite thin films as the light‐emitting layer are reported. By controlling the molar ratios of organic salt (benzylammonium iodide) to inorganic salts (cesium iodide and lead iodide), luminescent quasi‐2D perovskite thin films are obtained with tunable emission colors from red to deep red. The perovskite/polymer composite approach enables quasi‐2D perovskite/PEO composite thin films to possess much higher photoluminescence quantum efficiencies and smoothness than their neat quasi‐2D perovskite counterparts. Electrically driven LEDs with emissions peaked at 638, 664, 680, and 690 nm have been fabricated to exhibit high brightness and external quantum efficiencies (EQEs). For instance, the perovskite LED with an emission peaked at 680 nm exhibits a brightness of 1392 cd m⁻²and an EQE of 6.23%. Moreover, exceptional electroluminescence spectral stability under continuous device operation has been achieved for these red perovskite LEDs.

    

   more » « less