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This PhD thesis presents research conducted within the framework of the SBO project "Quantum Dots for On-Chip Luminescent Downconversion (QDoCCO)". The project's main goals were the development of novel InP quantum dots, the investigation of innovative encapsulation methods for these nano-particles,
and the creation of spectrum-by-design LED demonstrators using InP quantum dots. This final goal, the realization of spectrum-by-design demonstrators, using accurate optical simulations for their design, forms the core scientific focus of this thesis. This research rationale stems from the transformative role of LEDs in the lighting and display industry due to their high energy efficiency and spectral design capabilities. However, conventional LEDs still face important challenges like the green gap and the limited color rendering of typical phosphor-converted white LEDs. These limitations can be mitigated by using quantum dots as luminescent materials. Quantum dots (QDs), in particular InP-based QDs, offer distinct advantages over traditional phosphors due to their narrow and tunable emission spectra, nanoscale size, short decay time and high absorption coefficient. Despite these advantages, achieving stable and efficient on-chip QD-LEDs remains challenging because the durability of QD-LEDs depends on the QD stability, and their efficiency is affected by QD re-absorption losses.
The primary research objectives of this thesis were to develop optical models to simulate QD-on-chip LED behavior using InP QDs, and to design and fabricate spectrum-by-design demonstrators for applications such as high color rendering lighting and optimal circadian lighting, and efficient displays with high color gamut. The main research contributions include: • Optical models for QD-LEDs : Two optical models for simulating QDs, varying in the number of input parameters and the precision of their outcomes, were proposed in this thesis. • High-CRI white LEDs with InP QDs : Efficient, high CRI white LEDs were demonstrated by combining InP QDs with traditional powder phosphors. This research highlights the potential of InP QDs to replace cadmium-based QDs in high-CRI applications. • Monochromatic InP QD-LEDs : Over 50% color conversion efficiency and wall-plug efficiencies above 30% for pure green, amber, and red QDLEDs using InP QDs with nearly perfect photoluminescence quantum yield, were achieved. Furthermore, a comparison of the efficiency of such monochromatic QD-LEDs when excited with violet light (~405 nm) and blue light (~450 nm) was performed.
• Spectrum-by-design light sources : This research demonstrates the potential of InP QDs to customize LED spectra for specialized applications like circadian lighting and display lighting. In conclusion, this thesis demonstrates the feasibility of using InP-based QDs for efficient, high-CRI white LEDs and spectrum-by-design solutions. The developed models and demonstrators offer valuable insights for future research and commercial applications in lighting and display technologies.