Commercial white LEDs (WLEDs) use yellow-emitting cerium-doped yttrium aluminum garnet phosphor, along with an InGaN-based blue LED. However, such phosphors suffer from the following disadvantages: (1) limited phosphor performance due to thermal degradation, (2) significant backscattering losses, and (3) poor absorption. Current commercial WLEDs have a luminous efficacy varying from 75~100 lm/W, with some showing higher values, but with a trade-off in the color rendering indices (CRIs). To work towards the US Department of Energy target of a luminaire of 200 lm/W, it is necessary to develop new designs for phosphors for WLEDs with high efficiency and better color rendering.
Here, we propose and study theoretically core-shell (CS) and core-shell-shell (CSS) metal-semiconductor nanowires (NWs) as phosphor components in white LEDs, using a Mie formalism for absorption and a Green’s function approach for emission. Coupling of the plasmon resonance oscillations at the metal surface with the electric fields of the incident light enables an enhanced absorbance of CS NWs of 0.6-0.9 for blue light compared to the absorbance of 0.2-0.4 observed in the CS quantum dots. We have predicted that the External Quantum Efficiency (EQE) can be enhanced by almost 11 times for red phosphors, by 36 times for yellow phosphors and as high as four orders of magnitude for the green phosphors relative to the bare semiconductor nanowires, when carefully choosing the semiconductor and metal materials and dimensions. CSS NWs further improve values of the EQE by as much as 60% relative to the CS nanowires for red phosphors and 3 times for yellow phosphors, due to the addition of another enhanced electric field from the semiconductor core to the Purcell factor.