Tuning the emission color of lanthanide-doped tungstate nano- and micromaterials: towards white light generation

 In a world where environmental impact is a big issue, also alternative energy saving lighting devices are being investigated. Moving away from the classic but inefficient light bulb, solid-state lighting materials to be used in (O)LEDs are currently in the center of attention. One important challenge in that area of research is the development of a single material that emits a natural white light with high efficiency and long operational lifetime. Rare-earth tungstates are promising materials for white light generation as the tungstate matrix itself emits a bluish color, which can yield white light in combination with the characteristic narrow-line emission of doped lanthanide ions. In this thesis project you will synthesize Ln³⁺- doped rare-earth tungstate nano- and micromaterials. You will investigate the factors influencing the growth of the particles towards different morphologies, such as reaction temperature, duration, stabilizing ligands, etc. You will then characterize the materials by powder X-ray diffraction, transmission and scanning electron microscopy (TEM and SEM), and finally study the luminescence properties. You will display the true color of the emitted light on a so-called “CIE-diagram”, as seen in the picture.

Inkjet printing of luminescent thin films containing lanthanide-doped nanophosphors

Due to their efficient luminescence, purely inorganic lanthanide-doped materials have certain benefits over “organic” coordination compounds, which can suffer from vibrational luminescence quenching. Processing inorganic salts, however, into flexible materials that are needed for high-end applications, can be troublesome, because of the incompatibility of the inorganic matrix with the oganic nature of the substrate (often polymer materials).

One way of dealing with this problem is making the inorganic compound into nano-sized particles, which are dispersible in organic solvents and as such no longer incompatible with organic substrate materials.

In this thesis subject, you will synthesize inorganic lanthanide-doped nanoparticles for making stable colloidal suspensions, which can be inkjet printed onto different substrates. You will investigate the parameters that influence the stability of the suspensions (size of the particles, presence of stabilizing ligands, concentration, type of solvent...), and study these suspensions for inkjet printing in the SCRiPTS group. You will optimize the printing parameters in order to achieve the highest quality thin films, which will then be studied for their luminescence properties in the Luminescent Lanthanide Lab.

Synthesis and structural elucidation of a family of luminescent lanthanide-based carboxylate MOFs

Metal-organic frameworks (MOFs) are coordination polymers in which metal ions are interconnected by multifunctional linker molecules, resulting in a three-dimensional network with properties that are often very different from the corresponding mononuclear metal complexes. Many of these MOFs are porous, allowing the take-up of gas molecules (e.g. for CO₂ capture or H₂ storage or for catalytic applications). Lanthanide MOFs have the typical advantage of showing characteristic narrow-line luminescence, which can be exploited in new generations of sensors (e.g. luminescence modulation depending on the uptake of specific types of gas molecules).Because of the rich coordination chemistry of lanthanides, predicting the structure of a lanthanide MOF is virtually impossible. However, important information on how these materials are formed can be obtained by variation of experimental parameters when synthesizing lanthanide MOFs.

In this project, you will use known synthetic procedures to make a family of lanthanide MOFs, with the aim of elucidating their crystal structure. You will study the influence of different experimental parameters on the final crystal structure formed and on the resulting stability, porosity, luminescence properties, etc. ...

This project will be carried out in collaboration with prof. K. Van Hecke (XStruct).

Design and synthesis of novel lanthanide-chelating ligands for luminescent applications

Coordination chemistry is not just about making complexes with commercially available ligands: designing and synthesizing new ligands can be a challenging but rewarding part of the job as well. For those interested in organic as well as inorganic chemistry, this project offers the right ingredients. Using two families of molecular architectures that have not yet been studied as lanthanide complexants, you will decide which functional groups to introduce in order to optimize both the complex forming efficiency as the luminescent properties. This will require a sound organic chemistry basis, as the first part of the project will be carried out in the lab of prof. J. Van der Eycken (Department of Organic Chemistry). When the first ligand systems will be purified and ready, you will bring them to the Luminescent Lanthanide Lab to make complexes with lanthanides, after which you will try to elucidate the molecular structure (in collaboration with prof. K. Van Hecke) and finally study the luminescence properties of your new materials. This is a truly multidisciplinary research project.

Spectroscopic and theoretical investigation of lanthanide-doped infrared-emitting glasses

At the longer wavelength side of the electromagnetic spectrum, “light” in the infrared can no longer be perceived by the human eye, but can nevertheless have substantial importance. So-called “near-infrared” radiation (having wavelengths between 750 and 3000 nm) is already being used for optical data communication, as the scattering losses in optical fibres decrease with the fourth power of the wavelength. “Light” beyond 3000 nm is known as “mid-infrared”, a region in which many molecules (e.g. in food industry, safety and health related molecules, explosives, ...) absorb light at specific wavelengths, because of typical stretching and bending frequencies of molecular functional groups. In order to use this mid-infrared region for analytical purposes, e.g. in quality control, novel light sources are needed, that emit at distinct wavelengths in this region. Apart from these applications, research towards mid-infrared lasers situated in the military field is also steadily increasing, e.g. for collision-avoidance systems, etc.

Glass matrices that are transparent up to the mid-infrared are highly uncommon and have to be custom-made in specialized research labs. The Luminescent Lanthanide Lab therefore collaborates with the “Equipe Verres et Céramiques” from Rennes University, France. They have decades of expertise in glass formulation and synthesis and make “low-phonon” (i.e. having very low vibrational frequencies to avoid emission quenching) chalcogenide glasses doped with lanthanide ions.

In this project, you will perform a full spectroscopic investigation of a small series of high-specialty near- and mid-infrared emitting lanthanide-doped glasses. Based on an absorption spectrum that you will record, you will perform a Judd-Ofelt analysis in order to derive three phenomenological parameters Ω₂, Ω₄ and Ω₆, which describe the spectroscopic behaviour of the doped lanthanide ions in a semi-quantitative way. In a second part of the project, you will use specialized equipment, including high-power lasers, to record the near- and mid-infrared emission from the doped glasses. If you’re not scared by a mathematical formula, and you have sufficient instrumental skills, this is your project!