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1. 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. 

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2. 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. 

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3. Efficient Broadband Near‐Infrared Emission in the GaTaO 4 :Cr 3+ Phosphor

   https://doi.org/10.1002/adom.202101800  

   Zhong, Jiyou ; Zhuo, Ya ; Du, Fu ; Zhang, Hongshi ; Zhao, Weiren ; You, Shihai ; Brgoch, Jakoah ( November 2021 , Advanced Optical Materials)

   Efficient broadband near‐infrared (NIR) emitting materials with an emission peak centered above 830 nm are crucial for smart NIR spectroscopy‐based technologies. However, the development of these materials remains a significant challenge. Herein, a series of design rules rooted in computational methods and empirical crystal‐chemical analysis is applied to identify a new Cr³⁺‐substituted phosphor. The compound GaTaO₄:Cr³⁺emerged from this study is based on the material's high structural rigidity, suitable electronic environment, and relatively weak electron–phonon coupling. Irradiating this new phosphor with 460 nm blue light generates a broadband NIR emission (λ_em,max = 840 nm) covering the 700–1100 nm region of the electromagnetic spectrum with a full width at half maximum of 140 nm. The phase has a high internal quantum yield of 91% and excellent thermal stability, maintaining 85% of the room temperature emission intensity at 100 °C. Fabricating a phosphor‐converted light‐emitting diode device shows that the new compound generates an intense NIR emission (178 mW at 500 mA) with photoelectric efficiency of 6%. This work not only provides a new material that has the potential for next‐generation high‐power NIR applications but also highlights a set of design rules capable of developing highly efficient long‐wavelength broadband NIR materials.

    

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4. Identifying an efficient, thermally robust inorganic phosphor host via machine learning

   https://doi.org/10.1038/s41467-018-06625-z  

   Zhuo, Ya ; Mansouri Tehrani, Aria ; Oliynyk, Anton O. ; Duke, Anna C. ; Brgoch, Jakoah ( October 2018 , Nature Communications)

   Rare-earth substituted inorganic phosphors are critical for solid state lighting. New phosphors are traditionally identified through chemical intuition or trial and error synthesis, inhibiting the discovery of potential high-performance materials. Here, we merge a support vector machine regression model to predict a phosphor host crystal structure’s Debye temperature, which is a proxy for photoluminescent quantum yield, with high-throughput density functional theory calculations to evaluate the band gap. This platform allows the identification of phosphors that may have otherwise been overlooked. Among the compounds with the highest Debye temperature and largest band gap, NaBaB₉O₁₅shows outstanding potential. Following its synthesis and structural characterization, the structural rigidity is confirmed to stem from a unique corner sharing [B₃O₇]^5–polyanionic backbone. Substituting this material with Eu²⁺yields UV excitation bands and a narrow violet emission at 416 nm with a full-width at half-maximum of 34.5 nm. More importantly, NaBaB₉O₁₅:Eu²⁺possesses a quantum yield of 95% and excellent thermal stability.

    

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5. Combining experiment and computation to elucidate the optical properties of Ce 3+ in Ba 5 Si 8 O 21

   https://doi.org/10.1039/c9cp05576b  

   Zhong, Jiyou ; Hariyani, Shruti ; Zhuo, Ya ; Zhao, Weiren ; Liu, Xiang ; Wen, Jun ; Brgoch, Jakoah ( January 2020 , Physical Chemistry Chemical Physics)

   Complex alkaline earth silicates have been extensively studied as rare-earth substituted phosphor hosts for use in solid-state lighting. One of the biggest challenges facing the development of new phosphors is understanding the relationship between the observed optical properties and the crystal structure. Fortunately, recent improvements in characterization techniques combined with advances in computational methodologies provide the research tools necessary to conduct a comprehensive analysis of these systems. In this work, a new Ce 3+ substituted phosphor is developed using Ba 5 Si 8 O 21 as the host crystal structure. The compound is evaluated using a combination of experimental and computational methods and shows Ba 5 Si 8 O 21 :Ce 3+ adopts a monoclinic crystal structure that was confirmed through Rietveld refinement of high-resolution synchrotron powder X-ray diffraction data. Photoluminescence spectroscopy reveals a broad-band blue emission centered at ∼440 nm with an absolute quantum yield of ∼45% under ultraviolet light excitation ( λ ex = 340 nm). This phosphor also shows a minimal chromaticity-drift but with moderate thermal quenching of the emission peak at elevated temperatures. The modest optical response of this phase is believed to stem from a combination of intrinsic structural complexity and the formation of defects because of the aliovalent rare-earth substitution. Finally, computational modeling provides essential insight into the site preference and energy level distribution of Ce 3+ in this compound. These results highlight the importance of using experiment and computation in tandem to interpret the relationship between observed optical properties and the crystal structures of all rare-earth substituted complex phosphors. 

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