First-Principle Calculation of Paramagnetic NMR Shifts in Lanthanide-Doped Solid-State Lighting Phosphor Materials

Dnr:

SNIC 2017/1-280

Type:

SNAC Medium

Principal Investigator:

Andrew Pell

Affiliation:

Stockholms universitet

Start Date:

2017-06-08

End Date:

2018-07-01

Primary Classification:

10402: Fysikalisk kemi

Webpage:

http://www.su.se/profiles/apell-1.255858

Allocation

Abstract

Phosphor converted inorganic light-emitting diodes constitute one of the most promising pathways for an efficient and durable general light source with low environmental impact. Among these group of materials, yttrium aluminum garnet (Y3Al5O12; YAG) doped (~1 wt %) with Ce3+ ions (Y3Al5O12:Ce3+) exhibits excellent photoluminescence properties: advantageous emission spectrum, high quantum efficiency, and elevated luminescence quenching temperature among others [1]. Calcium scandate CaSc2O4:Ce3+, an extremely efficient emitter at very low doping levels, constitutes another encouraging candidate [2]. The local structure around Ce3+ ion is the key to the improved luminescent properties. This has motivated recent NMR studies of nuclei in close proximity to Ce3+. NMR signals of these nuclei are shifted in the spectrum due to hyperfine interaction with the unpaired electron of lanthanide ion. However, this paramagnetic shift is poorly understood from a theoretical stand point, with the only description to date relying on simplified model of the electronic structure [3, 4]. In this project we aim to gain insight specifically into local structural effects due to dilute activating ions by exploring the extended series of YAG:Ln3+/CaSc2O4:Ln3+ samples doped with different lanthanide dopants from Ce3+ to Yb3+. By probing NMR responses of the nuclei in close adjacency to paramagnetic lanthanide activators, we aim to provide better understanding of the interactions arising thereof, owing not only to importance of such compounds from the materials chemistry perspective, but to evaluate properties such as the crystal-field parameters. Theoretical predictions of paramagnetic NMR shifts of nuclei at the distinct crystallographic positions with respect to the Ln3+ ion are crucial for correct signal assignments in order to grasp the essential information. The purpose of this application is to get access to computer resources, which will allow us to perform challenging calculations of paramagnetic NMR shifts with the state-of-the-art, recently developed quantum chemistry formalism and methods within the density functional theory (DFT) of Vaara et al. [5, 6] with whom we have a close collaboration. These methods have currently been extended to lanthanides, and will be applied for the first time in these systems. The obtained results will be compared with predictions based on the existing models in the literature, and new experimental NMR data. Our proposed project is right at the forefront of research into both paramagnetic NMR, and the development and study of new phosphor materials. [1] George, N. C. et al. Chem. Mater. 2013, 25, 3979-3995. [2] Chen, Y. et al. J. Lumin. 2011, 131, 1770-1775. [3] Bleaney B. J. Mag. Res. 1972, 8, 91-100. [4] Golding R. M. et al. Aust. J. Chem. 1972, 25, 2577-2581. [5] Teemu O. et al. PRL 2008, 100, 133002. [6] Vaara J. et al. J. Chem. Theory Comput. 2015, 11, 4840-4849