Colour optimization of phosphor-converted flexible nitride nanowire white light emitting diodes

Abstract

We demonstrate flexible nanowire white light-emitting-diodes (LEDs) with an optimized colour quality. The devices consist of flexible InGaN/GaN nanowire LEDs acting as pumps, capped with removable phosphor-doped polydimethylsiloxane membranes. Five different phosphors with tens of microns in grain size emitting from green to orange are investigated using both violet-blue and a bluegreen nanowire-based LED pumps. In addition, a flexible nanowire white LED with a warm white emission is demonstrated using two layers of different phosphors. Compared to the previous realizations of flexible nanowire white LEDs, these novel LEDs improve the colour rendering index from 54 to 86 and show a colour tuneable from a bluish cool white colour to natural white and finally to warm white. The flexibility tests show that the LEDs can be bent down to 1.5 cm curvature radius without significant degradation. Therefore, the replacement of the nano-phosphors used in the previous realization by relatively inexpensive micro-phosphors does not degrade the good mechanical flexibility of the white nanowire LEDs.

Progress and Challenges of InGaN/GaN-Based Core–Shell Microrod LEDs

“…The first flexible phosphor-converted white microrod LED is depicted in Figure 7 e; it had a CCT of 6306 K, a CRI of 54, and an EQE of 9.3%. The CRI was later improved to a value of 65 by using two layers of yellow and orange phosphors [ 4 ].…”

“…The unique three-dimensional (3D) architecture promises novel properties that may be attractive for solid-state lighting or even open further application fields of GaN-based LEDs. These include (flexible) white LEDs [ 3 , 4 ], single-photon sources [ 5 ], and high-frequency LEDs [ 1 , 6 ]. Microrod LEDs have a high surface-to-volume ratio, creating an enlarged light output area for the same chip size [ 7 ].…”

The application of phosphor Sr4La(PO4)3O:Ce3+,Tb3+,Mn2+ on the white-LEDs: luminescence and power transmission characteristics

“…The Kubelka-Munk (K-M) equation was used to calculate the absorption spectra for SLPO from its scattered spectra in order to experimentally determine the SLPO compound optic bandspace magnitude [24], which is expressed as (1). The Tauc connection links the bandgap E g and α with the straight absorption coefficient of a substance [25], as used in (2).…”

Dual‐Color Emission from Monolithic m‐Plane Core–Shell InGaN/GaN Quantum Wells

“…[ 22–25 ] Nanowire‐based LEDs with blue core/shell InGaN/GaN MQWs combined with phosphors reach measured external quantum efficiency as high as 9% for white light emission. [ 26–28 ] Core–shell InGaN/GaN heterostructures can also exhibit multicolor emission related to different indium incorporation on specific crystallographic facets and edges. [ 29–31 ] For instance, Choi et al reported orthogonally polarized dual‐wavelength emission from InGaN/GaN core–shell microrod arrays due to different indium content in the m ‐plane facets compared with the edges leading to spatially separated blue and green emissions.…”