PhD in Metallic nanoparticles to control the angular emission of phosphors

Supervisors: François Réveret (francois.reveret@uca.fr / 04 73 40 75 39) 

Damien Boyer (damien.boyer@sigma-clermont.fr / 04 73 40 76 47) 

Laboratory: “Matériaux Luminescents” group at “Institut de Chimie de Clermont-Ferrand” 

Context: Phosphor materials are considered key components to produce light emission in common applications such as light emitting diode (LED) based lightning and display devices. UV or blue LED are used to excited phosphor and its emission depends on the material nature. For example, a white LED is composed by a blue LED with a yellow phosphor. Optoelectronic devices have to be efficient and compact with low energy consumption. In mobile systems for automobile and aviation sectors or augmented reality and holographic displays, the angular distribution tuneability of emitted light is essential for directional lighting [1]. Today the directionality of the emitted light is controlled with bulky optical systems (lens, mirrors) which is not compatible with nomad or compact applications. In this context nanophotonic could bring versatile solutions. The surface of the phosphor layer could be structured at the nano or micro-scale to control the emission directionality and also to improve the light extraction [2]. However, these methods are expensive and could affect the optical properties of the phosphor. 

Project and objectives: Here we propose to combine metallic nanoparticles (MNPs) with phosphor layer. This method is easy to realize, cheap and does not damage the phosphor layer. The use of MNPs allow to control the emission directionality [3] and also to enhance both light injection and extraction [4]. Recently we have evidenced the efficiency of silver nanocubes (Figure 1) to enhance light extraction of a YAG:Ce coating (phosphor commonly used in white light emitting diode) [4]. In this work MNPs are used as optical scatterers, this new approach appears very promising to control finely the light output. 

The PhD student will first synthesize phosphor materials with controlled size through different processes (sol-gel process, solvothermal and thermolysis routes). Luminescent coatings (LC) will be deposed on transparent substrate with spin-coating. Then commercial MNPs will be dispersed on the LC surface. Different methods (drop casting, spin coating, Langmuir Blodgett) will be tested to control the MNPs density and homogeneity. The shape (nanocubes, nanospheres, nanoprisms), the size (25 to 100 nm), the nature (gold, silver, aluminium) and the density of the MNPs will be carefully investigated to identify optimal designs in term of efficiency and directionally control. 

Phosphor materials, LCs with and without MNPs will be studied through structural and morphological characterisations available at ICCF. Optical properties will be investigated with spatially and angular resolved photoluminescence and also time resolved measurements. 

Expected profile: The candidate should have a Master degree or equivalent in chemistry of inorganic materials or in physical chemistry materials. The candidate should be motivated for an experimental work in an interdisciplinary project. Knowledge in optical spectroscopy will be appreciated. 

References 

[1] Dagens, B. et al. Photoniques 115, 34 (2022) 

[2] Leung, S.-F. et al. The journal of physical chemistry letters 5 (8), 1479 (2014) 

[3] Lozano, G.; et al. Light: Science & Applications 2, e66 (2013)

[4] Khaywah, M.; et al. J. Phys. Chem. C 125, 7780 (2021)