Green phosphor-converted LED with LPDF aims at ultrahigh efficiency

A research group at Kookmin University and PSI Co. is touting the high efficiency and other properties of green LEDs that consist of a blue LED, a phosphor that converts blue to green, and a long-pass dichroic filter (LPDF) that filters out the remaining blue light.

A green phosphor-coated LED designed with a long-pass dichroic filter (LPDF) has higher luminous efficacy than one designed without a filter
A green phosphor-coated LED designed with a long-pass dichroic filter (LPDF) has higher luminous efficacy than one designed without a filter

A research group at Kookmin University (Seoul, Korea) and PSI Co. (Kyungki-Do, Korea) is touting the high efficiency and other properties of green LEDs that consist of a blue LED, a phosphor that converts blue to green, and a long-pass dichroic filter (LPDF) that filters out the remaining blue light. This type of phosphor-coated LED (pc-LED) compares favorably with LEDs that combine a blue LED and green phosphor but without an LPDF, because such LEDs require a thicker layer of phosphor to block out all the blue light, reducing total green light output in the process.

A green phosphor-coated LED designed with a long-pass dichroic filter (LPDF) has higher luminous efficacy than one designed without a filterA green phosphor-coated LED designed with a long-pass dichroic filter (LPDF) has higher luminous efficacy than one designed without a filter

Standard gallium-nitride-based green LEDs suffer from both low electroluminescence efficiency and considerable efficiency droop (lower efficiency at higher currents). Thus, many worldwide are attempting to create green LEDs that operate via a different approach. The Korean group’s version consists of a 445-nm-emitting blue LED, a phosphor with a peak wavelength that can range from 515 to 560 nm depending on composition, and a multilayer LPDF. Measured luminous efficacies range from 143 to 173 lm/W depending on the phosphor composition, with the external quantum efficiencies of the green LEDs falling in the range of 0.31 to 0.35. With a better blue LED and better optics and packaging, the researchers hope for luminous efficacies of 286 to 315 lm/W. Contact Young Rag Do at [email protected].

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