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1. Gd ³⁺ -activated narrowband ultraviolet-B persistent luminescence through persistent energy transfer

   https://doi.org/10.1039/D1DT00120E  

   Wang, Xianli; Chen, Yafei; Kner, Peter A.; Pan, Zhengwei (March 2021, Dalton Transactions)

   null (Ed.)

   This work reports the realization of Gd 3+ persistent luminescence in the narrowband ultraviolet-B (NB-UVB; 310–313 nm) through persistent energy transfer from a sensitizer of Pr 3+ , Pb 2+ or Bi 3+ . We propose a general design concept to develop Gd 3+ -activated NB-UVB persistent phosphors from Pr 3+ -, Pb 2+ - or Bi 3+ -activated ultraviolet-C (200–280 nm) or ultraviolet-B (280–315 nm) persistent phosphors, leading to the discovery of ten Gd 3+ NB-UVB persistent phosphors such as Sr 3 Gd 2 Si 6 O 18 :Pr 3+ , Sr 3 Gd 2 Si 6 O 18 :Pb 2+ and Y 2 GdAl 2 Ga 3 O 12 :Bi 3+ as well as five ultraviolet-B persistent phosphors such as Y 3 Al 2 Ga 3 O 12 :Pr 3+ , Sr 3 Y 2 Si 6 O 18 :Pb 2+ and Y 3 Al 2 Ga 3 O 12 :Bi 3+ . The persistent energy transfer from the sensitizers to Gd 3+ is very efficient and the Gd 3+ NB-UVB afterglow can last for more than 10 hours. This study expands the persistent luminescence research to the NB-UVB as well as the broader ultraviolet-B spectral regions. The NB-UVB persistent phosphors may act as self-sustained glowing NB-UVB radiation sources for dermatological therapy. 

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2. A new up-conversion charging concept for effectively charging persistent phosphors using low-energy visible-light laser diodes

   https://doi.org/10.1039/C8TC02419G  

   Chen, Yafei; Liu, Feng; Liang, Yanjie; Wang, Xianli; Bi, Jianqiang; Wang, Xiao-jun; Pan, Zhengwei (January 2018, Journal of Materials Chemistry C)

   It is general knowledge in persistent luminescence that high-energy illumination, mostly ultraviolet light, is usually necessary in order to effectively charge persistent phosphors. However, the need for high-energy ultraviolet light excitation compromises some applications. In his pioneering work on ruby (Al 2 O 3 :Cr 3+ ) laser materials in 1960, Theodore Maiman observed an excited-state absorption phenomenon under the excitation of a high-intensity green-light flash tube. Inspired by Maiman's observation, here we propose a new two-photon up-conversion charging (UCC) concept to effectively charge Cr 3+ -activated near-infrared persistent phosphors using low-energy, high-intensity visible-light laser diodes. As an example, we demonstrate that a low-energy 635 nm laser diode can produce persistent luminescence in the LiGa 5 O 8 :Cr 3+ persistent phosphor at the same magnitude as that produced by high-energy 335 nm ultraviolet light from a xenon arc lamp. Moreover, the UCC appears to be a common phenomenon in persistent phosphors containing other UCC-enabling activators such as rare-earth Pr 3+ ions and transition metal Mn 2+ ions. The UCC technique offers a new way to study persistent luminescence and utilize persistent phosphors; for instance, in bioimaging it makes effective in vivo charging persistent optical probes using tissue-friendly visible light possible. 

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3. Near-infrared photoluminescence of Portland cement

   https://doi.org/10.1038/s41598-022-05113-1  

   Meng, Wei; Bachilo, Sergei M.; Parol, Jafarali; Nagarajaiah, Satish; Weisman, R. Bruce (January 2022, Scientific Reports)

   Abstract Portland cement emits bright near-infrared photoluminescence that can be excited by light wavelengths ranging from at least 500–1000 nm. The emission has a peak wavelength near 1140 nm and a width of approximately 30 nm. Its source is suggested to be small particles of silicon associated with calcium silicate phases. The luminescence peak wavelength appears independent of the cement hydration state, aggregates, and mechanical strain but increases weakly with increasing temperature. It varies slightly with the type of cement, suggesting a new non-contact method for identifying cement formulations. After a thin opaque coating is applied to a cement or concrete surface, subsequent formation of microcracks exposes the substrate’s near-infrared emission, revealing the fracture locations, pattern, and progression. This damage would escape detection in normal imaging inspections. Near-infrared luminescence imaging may therefore provide a new tool for non-destructive testing of cement-based structures. 

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4. 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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5. 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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