Bredigite-structure orthosilicate phosphor as a green component for white LED: the structural and optical properties

Our plain-English summary of Bredigite-structure orthosilicate phosphor as a green component for white LED: the structural and optical properties, by K.H. Lee, S.H. Park, H.S. Yoon, et al (Optics Express, 2012).

The study

• Authors: K.H. Lee, S.H. Park, H.S. Yoon, Y.I. Kim, H.G. Jang, W.B. Im
• Journal: Optics Express
• Published: 2012;20(6):6248-57
• Cited by: 3 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

A green-emitting phosphor, Ca₁₄-xEuxMg₂[SiO₄]₈ (CMS:Eu²⁺), has been synthesized as a component of white light emitting diodes (WLEDs). The emission spectrum is broad, with a maximum at about 505 nm under 400 nm excitation due to the transition from the 4f⁶5d excited state to the 4f⁷-ground state of a Eu²⁺ ion. The dipole-dipole interaction was a dominant energy transfer mechanism of the electric multipolar character of CMS:Eu²⁺. The critical distance was calculated as 12.9 Å and 14.9 Å using a critical concentration of Eu²⁺ and Dexter's theory for energy transfer. When CMS:Eu²⁺ and red phosphor are incorporated with an encapsulant on an ultraviolet (λmax = 395 nm) light emitting diodes (LEDs), white light with a color rendering index of 91 under a forward bias current of 20 mA was obtained. The structural and optical characterization of the phosphor is described.

In plain English

This article is a laboratory materials-science study. It is not about asbestos or health. The authors made a green-glowing powder (a phosphor), CMS:Eu2+, for use in white light-emitting diodes (LEDs). It is a calcium magnesium silicate with the bredigite crystal structure, containing a small amount of europium. They studied its crystal structure and light emission and compared it with a commercial Sr2SiO4:Eu2+ phosphor. Under 400 nm light, the powder glowed with a peak at about 505 nm. The best europium level was x = 0.3. The authors calculated critical energy-transfer distances of 12.9 and 14.9 angstroms and concluded that energy passed between europium ions by dipole-dipole interaction. Its quantum efficiency was about 23 percent, compared with about 85 percent for the commercial phosphor. When heated from room temperature to 150 degrees C, its light output fell by 18 percent, compared with 11 percent for the commercial phosphor. A test LED combining CMS:Eu2+ with a commercial red phosphor gave white light with a color rendering index of about 91 at 20 mA.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory synthesis and characterization of a phosphor material (materials-science experiment), including fabrication of prototype LED devices
• Who was studied: No people or animals. The study used powder samples of the phosphor Ca14-xEuxMg2[SiO4]8 with varying europium content, compared with a commercial Sr2SiO4:Eu2+ phosphor, and prototype LEDs made with the phosphor.
• Main results:
  • For the optimized CMS:Eu2+ (x = 0.3) under 400 nm excitation, the emission was broad with a maximum at about 505 nm.
  • The optimum europium substitution was x = 0.3. Above that, emission intensity dropped (concentration quenching).
  • The critical energy-transfer distance was calculated as about 12.9 angstroms from the critical concentration, and as 14.9 angstroms from the Dexter formula.
  • The authors found that dipole-dipole interaction was the concentration quenching mechanism of Eu2+ emission in CMS:Eu2+.
  • Quantum efficiency under 400 nm excitation at room temperature was about 23% for CMS:Eu2+ and about 85% for the commercial Sr2SiO4:Eu2+ reference.
  • From room temperature to 150 degrees C, light intensity decreased by 11% for Sr2SiO4:Eu2+ and by 18% for CMS:Eu2+. The activation energies for thermal quenching were 0.348 eV for Sr2SiO4:Eu2+ and 0.158 eV for CMS:Eu2+.
  • The prototype LED (InGaN chip, 395 nm, with CMS:Eu2+ and a commercial red phosphor) had CIE chromaticity coordinates (0.33, 0.38), a color temperature of 5500 K and a color rendering index of about 91 at 20 mA. Luminous efficacy was 10 to 15 lm/W depending on the current.
• The authors' conclusion: The authors concluded that energy transfer between Eu2+ ions in this phosphor is an electric dipole-dipole interaction. They also concluded that applying CMS:Eu2+ (x = 0.3) to 395 nm InGaN LEDs gave white LEDs producing 13 lm/W at 20 mA, with a color rendering index of 91 and a 5500 K color temperature.
• Limitations the authors state:
  • The authors stated that they were still acquiring microscopic structural data needed to establish more accurately which crystal sites the europium occupies.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Tremolite.

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