Abstract
A variety of efficient green, yellow, and amber monochromatic phosphor-converted light-emitting diodes (pc-LEDs) were fabricated by simply capping a long-wave pass filter (LWPF) on top of LED packing associated with each corresponding powder phosphor. In this paper, the luminous efficacy and color purity of two green, three yellow, and two amber pc-LEDs were reviewed by comparing the optical properties and current/temperature stability of each LWPF-capped pc-LED. The simple combination of LWPFs and phosphor materials in the pc-LEDs provide a simple means of addressing the low luminous efficacy problem of III-V monochromatic semiconductor LEDs in the various colors of the wavelength range between green and amber (known as the "green gap"). This technique also represents a simple approach to mitigate the sub-linearity problem of the efficacy versus the driving current occurring at a relatively low current in III-V green LEDs (known as "green droop") to the level of a blue LED. This nano-multilayered filter-capped pc-LED can open further research into developing new color-converting materials (such as powder phosphors, and/or quantum dots) to extend the color palette in the wavelength region of the "green gap" and to improve the efficacy and color purity of color pc-LEDs.
Highlights
The beautiful mono-color generation of phosphor-converted light-emitting diodes is relevant when it is realized that the entire palette of colors of phosphors is available in the Commission Internationale d'Eclairage (CIE) chromaticity diagram
We suggested amber light phosphor-converted light-emitting diodes (pc-LEDs) using Eu-doped silicate powder phosphors in association with a blue-mirror-yellow-pass filter
The best architecture of pump LED, the highest efficient phosphor, or the best optical structure of the phosphor layer were not used in this experiment, this simple combination of a pc-LED and a long-wave pass filter (LWPF) nano-multilayered film represents a simple means of realizing the entire palette of colors in the CIE chromaticity diagram from efficient full downconverted, mono-chromatic LEDs given the availability of color-converting materials such as powder phosphors or quantum dots
Summary
The beautiful mono-color generation of phosphor-converted light-emitting diodes (pc-LEDs) is relevant when it is realized that the entire palette of colors of phosphors is available in the Commission Internationale d'Eclairage (CIE) chromaticity diagram. A modified quarter-wave type of LWPF consisting of nano-multilayered film was introduced on top of an amber phosphor-coated InGaN-based LED die to block and recycle unabsorbed transmitted blue emission to create a highly efficient amber monochromatic LED [11]. This concept can be enlarged to create a variety of monochromatic color LEDs because there are a large number of powder phosphors or quantum dots in the present market or in research labs use well-established technology. This straightforward concept of monochromatic pc-LEDs can open research and development areas related to the production of new color-converting materials to be used in green/yellow/amber phosphors and new types of omnidirectional reflective (ODR) filters or 1D/3D photonic crystal filters which function as blue-mirror-yellow-pass filters
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