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1. 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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2. Realizing Wide‐Gamut Human‐Centric Display Lighting with K 3 AlP 3 O 9 N:Eu 2+

   https://doi.org/10.1002/adom.202202689  

   Hariyani, Shruti ; Xing, Xinxin ; Amachraa, Mahdi ; Bao, Jiming ; Ong, Shyue Ping ; Brgoch, Jakoah ( February 2023 , Advanced Optical Materials)

   Computers, televisions, and smartphones are revolutionized by the invention of InGaN blue light‐emitting diode (LED) backlighting. Yet, continual exposure to the intense blue LED emission from these modern displays can cause insomnia and mood disorders. Developing “human‐centric” backlighting that uses a violet‐emitting LED chip and a trichromatic phosphor mixture to generate color images is one approach that addresses this problem. The challenge is finding a blue‐emitting phosphor that possesses a sufficiently small Stokes’ shift to efficiently down‐convert violet LED light and produce a narrow blue emission. This work reports a new oxynitride phosphor that meets this demand. K₃AlP₃O₉N:Eu²⁺ exhibits an unexpectedly narrow (45 nm, 2206 cm⁻¹), thermally robust, and efficient blue photoluminescence upon violet excitation. Computational modeling and temperature‐dependent optical property measurements reveal that the narrow emission arises from a rare combination of preferential excitation and site‐selective quenching. The resulting chromaticity coordinates of K₃AlP₃O₉N:Eu²⁺ lie closer to the vertex of the Rec. 2020 than a blue LED chip and provides access to ≈10% more colors than a commercial tablet when combined with commercial red‐ and green‐emitting phosphors. Alongside the wide gamut, tuning the emission from the violet LED and phosphor blend can reduce blue light emissions to produce next‐generation, human‐centric displays.

    

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3. 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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4. 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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5. Local environment rigidity and the evolution of optical properties in the green-emitting phosphor Ba 1−x Sr x ScO 2 F:Eu 2+

   https://doi.org/10.1039/D1TC05411B  

   Hariyani, Shruti ; Amachraa, Mahdi ; Khan, Mariam ; Ong, Shyue Ping ; Brgoch, Jakoah ( February 2022 , Journal of Materials Chemistry C)

   Developing chemically and thermally stable, highly efficient green-emitting inorganic phosphors is a significant challenge in solid-state lighting. One accessible pathway for achieving green emission is by forming a solid solution with superior blue-emitting materials. In this work, we demonstrate that the cyan-emission ( λ em = 481 nm) of the BaScO 2 F:Eu 2+ perovskite can be red-shifted by forming a solid solution following (Ba 1− x Sr x ) 0.98 Eu 0.02 ScO 2 F ( x = 0, 0.075, 0.15, 0.25, 0.33, 0.40). Although green emission is achieved ( λ em = 516 nm) as desired, the thermal quenching (TQ) resistance is reduced, and the photoluminescence quantum yield (PLQY) drops by 65%. Computation reveals the source of these changes. Surprisingly, a basic density functional theory analysis shows the gradual Sr Ba substitution has negligible effects on the band gap ( E g ) energy, suggesting the activation energy barrier for the thermal ionization quenching remains unchanged, while the nearly constant Debye temperature indicates no loss of average structural rigidity to explain the decrease in the PLQY. Instead, temperature-dependent ab initio molecular dynamics (AIMD) simulations show that gradual changes of the Eu 2+ ion's local coordination environment rigidity are responsible for the drop in the observed TQ and PLQY. These results express the need to computationally analyze the local rare-earth environment as a function of temperature to understand the fundamental origin of optical properties in new inorganic phosphors. 

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