Luminescente Nanokristallen: Lijnverbreding en vormingsmechanismen

Abstract

Nanomaterials have become an increasingly important class of materials in the past decades due to their size-tunable optical, electronic, and magnetic properties. Nanomaterials are not only of great scientific interest, but their versatility has also resulted in a wide range of applica¬tions. This thesis focuses on two types of luminescent (light-emitting) nanomaterials, cadmium chalcogenide nanocrystals (NCs) and NaYF4 NCs doped with rare earth ions (lanthanides, e.g., erbium and ytterbium). Both the optical properties and nanocrystal growth mechanisms are investigated. Semiconductor NCs, especially CdSe nanoplatelets (NPLs), exhibit narrow emission bands in the visible part of the spectrum, a property needed for more efficient white light LEDs (w-LEDs) and vibrant displays. In these applications, the luminescent materials operate at elevated tem¬peratures, which affects the emission linewidth. Insight into this thermal broadening is important for application in w-LEDs but has so far not been investigated over a temperature range that is relevant for these applications. In this thesis, I report on the temperature-dependent spectral linewidth of cadmium chalcogenide NPLs and QDs. NaYF4 NCs doped with lanthanide ions are efficient upconversion materials that can convert two low-energy infrared photons to one high-energy visible photon. These materials can be used in deep-tissue imaging and to enhance the efficiency of solar cells. The formation mechanism of both NaYF4 NCs and CdSe NPLs is still debated. Control over the NC growth is essential to adjust the NC properties. In this thesis, I report on the mechanisms of their nucleation and growth, monitored using in situ absorption and x-ray scattering techniques.