New red phosphor ceramic K₂SiF₆:Mn⁴⁺

Journal Article · Tue Jul 07 00:00:00 EDT 2020 · Optical Materials

DOI:https://doi.org/10.1016/j.optmat.2020.110140· OSTI ID:1638691

Osborne, R. A. ^[1]; Cherepy, N. J. ^[1]; Seeley, Z. M. ^[1]; Payne, S.A. A. ^[1]; Drobshoff, A. D. ^[1]; Srivastava, A. M. ^[2]; Beers, W. W. ^[2]; Cohen, W. W. ^[2]; Schlagel, D. L. ^[3]

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1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
2. GE Current, Cleveland, OH (United States)
3. Ames Lab., Ames, IA (United States)

We report a new transparent ceramic phosphor for use in LED lighting has been fabricated. The previously reported and optimized narrow-emitting red phosphor, K₂SiF₆:Mn⁴⁺ (KSF), has been consolidated into a transparent ceramic phosphor for the first time, accomplished via hot-pressing the feedstock phosphor powder in a die under vacuum. KSF ceramics were fabricated with varying doping concentrations of Mn⁴⁺ and their properties studied. The absorption and emission spectra of the ceramics were identical to the feedstock phosphor powders and are ideal for LED lighting with strong absorption at 450 nm and narrow emission around 630 nm. The absorbance of the ceramics was directly proportional to the doping concentration. The ceramics were excited at various blue light fluxes and their emission intensities measured to study the effect of Mn⁴⁺ concentration on intensity-driven “droop” in the emission output. The ceramics with a lower Mn⁴⁺ doping were more efficient under higher light fluxes due to a decrease in Auger upconversion losses. KSF ceramics can allow a much longer path length of the diode light through the phosphor, as compared to phosphor-in-silicone, enabling the use of low optical absorption and the associated reduced activator concentration. The ceramics are measured to have a thermal conductivity of ~1.0 W/m-K, higher than that of phosphor-in-silicone or phosphor-in-glass. Several of these properties make KSF ceramics potentially desirable for use in white light LEDs. Greater thermal conductivity helps with heat dissipation, the lower surface area of the ceramic compared to the powder minimizes the environmental vulnerability of KSF, and the ability to lower the Mn⁴⁺ concentration reduces Auger recombination losses and mitigates the temperature rise, particularly at higher light flux.

• Research Organization: Ames Laboratory (AMES), Ames, IA (United States); Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA); USDOE Office of Energy Efficiency and Renewable Energy (EERE)
• Grant/Contract Number: AC02-07CH11358; AC52-07NA27344
• OSTI ID: 1638691
• Alternate ID(s): OSTI ID: 1765283; OSTI ID: 1637575
• Report Number(s): IS--J-10,221; LLNL-JRNL--810280
• Journal Information: Optical Materials, Journal Name: Optical Materials Journal Issue: C Vol. 107; ISSN 0925-3467
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
Droop
K2SiF6
LED phosphor
Phosphor ceramic
Red phosphor
Transparent ceramic