The realization of a whole palette of colors in a green gap by monochromatic phosphor-converted light-emitting diodes

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.