Recent advancements in semiconductor science and technology have enabled the development of niche commercial optoelectronic applications such as lasers, energy efficient light emitting diodes for lighting and displays. For the generation of white light emission, the current technology is based in two approaches. Currently commercially available white light is generated via the down-conversion of blue photons arising from an InGaN light emitting diodes (LED) to yellow/green-red light phosphor materials. Such approach lack of performance as it is still well below their potential luminous efficacy of up to 350 lm/W, with the down-conversion efficiency, color purity and operational frequency limited by the phosphor self-absorption losses, broad emission, and microsecond-long radiative lifetimes. On the second method, the integration of red, green, and blue LEDs (RGB) in one module produces white light based on proper mixture of the red, green, and blue emission. Blue and red electroluminescence in such schemes can be produced by high performance InGaN- and GaInP-based LEDs respectively, however efficient green emission remains challenging, while the integration of these devices on the same chip is a complex task to do. Recently a new class of materials known as lead halide perovskite nanocrystals (LHP NCs), have emerged as exceptional emitters with high luminescence efficiency, exceeding 90% in the green spectral region combined with narrow emission linewidths and tunability across the visible via facile ion exchange reactions. The characteristics of such nanomaterials renders them highly promising for optoelectronic and photonic applications.
The present project aims to develop, new and efficient hybrid emitter system based on the integration of III-nitride LEDs and LHP NCs, allowing them to exploit the strengths and potentials of both material families. The proposed work focuses on the study and optimization of the down-conversion of nitride emission involving the NCs using two approaches: (i) via radiative pumping in which UV/blue photons emitted from InGaN LEDs are absorbed by the LHP NCs and converted efficiently to longer wavelength photons, (ii) via Förster resonant energy transfer (FRET) in which energy channelling occurs non-radiatively via dipole-dipole coupling. The latter approach could overcome intrinsic limitations of the radiative pumping process which is relatively inefficient and slow. Eventually the synergy of processes (i) and (ii) will be sought to mediate the light emission process in the novel light emitting structures of the project.The development of novel and efficient white light LEDs, apart from the explicit applications in solid state lighting, will benefit several other commercial sectors such as displays, data communications, machine vision and biomedicine. For display applications, down-conversion via LHP NCs offers high colour saturation and purity due to their narrow emission linewidths. Visible light communication (LiFi) is expected to grow rapidly to meet the increasing demand of data transmission speed and bandwidths over the last years; the combination of nitrides with LHP NCs appears highly suitable for such applications, as they both exhibit fast radiative rates, allowing in principle such hybrid devices to operate at high modulation frequencies necessary for high data transmission rates. The aforementioned outcomes would greatly affect the wider society and public, as it is expected to have a great impact on the quality of life and economic growth in the future. The initial project objective is the study and optimization of the radiative- and non-radiative light down-conversion from an optically-pumped blue emitting LED based on InGaN/GaN multiple quantum wells (MQWs) to green/red absorbing LHP NC layers. In order to activate FRET, the use of nanostructured InGaN structures will be sought to allow a close proximity of nitride and NC excitations that can be coupled via the strong dipole-dipole interaction. The second objective of the project will be to develop the idea in order to demonstrate multicolor and white light emission via non-radiative and/or radiative pumping of LHP NCs from electrically excited, nanostructured InGaN-based LEDs. Finally, the project aims to investigate optically pumped LHP NCs for lasing applications, via electrical excitation of InGaN/GaN LEDs by employing a more elaborate structure design of a double-microcavity arrangement.
