Prospecting Lighting Applications with Ligand Field Tools and Density Functional Theory: A First-Principles Account of the 4f⁷–4f⁶5d¹ Luminescence of CsMgBr₃:Eu²⁺

Abstract

The most efficient way to provide domestic lighting nowadays is by light-emitting diodes (LEDs) technology combined with phosphors shifting the blue and UV emission toward a desirable sunlight spectrum. A route in the quest for warm-white light goes toward the discovery and tuning of the lanthanide-based phosphors, a difficult task, in experimental and technical respects. A proper theoretical approach, which is also complicated at the conceptual level and in computing efforts, is however a profitable complement, offering valuable structure-property rationale as a guideline in the search of the best materials. The Eu(2+)-based systems are the prototypes for ideal phosphors, exhibiting a wide range of visible light emission. Using the ligand field concepts in conjunction with density functional theory (DFT), conducted in nonroutine manner, we develop a nonempirical procedure to investigate the 4f(7)-4f(6)5d(1) luminescence of Eu(2+) in the environment of arbitrary ligands, applied here on the CsMgBr3:Eu(2+)-doped material. Providing a salient methodology for the extraction of the relevant ligand field and related parameters from DFT calculations and encompassing the bottleneck of handling large matrices in a model Hamiltonian based on the whole set of 33,462 states, we obtained an excellent match with the experimental spectrum, from first-principles, without any fit or adjustment. This proves that the ligand field density functional theory methodology can be used in the assessment of new materials and rational property design.

Photoluminescence properties of Yb2+ ions doped in the perovskites CsCaX3 and CsSrX3 (X = Cl, Br, and I) – a comparative study

“…57 DFTbased cluster calculations recently showed that this is a reasonably good assumption even if the ionic radii of the alkaline earth and lanthanide ions differ a lot. 61,67 The dependence on the metal-ligand distance is weak compared to expectations from classical crystal field theory (r À5 dependence), but gets closer to the estimations of the chemical shift model of Dorenbos attempted for Ce 3+ or Eu 2+ (r À2 dependence). 68 We found an r À1.2 dependence of 10 Dq of Yb 2+ for the halides CsMX 3 .…”

“…A clear assignment of all states can only be attempted upon inclusion of the full Hamiltonian, as performed by the theoretical approaches mentioned above. 33,35,36,60,61 However, it becomes clear from the spectra that the decoupled scheme affords very reasonable results in a simple manner and without calculation, which is particularly important for experimentalists.…”

Phosphors by Design: Approaches Toward the Development of Advanced Luminescent Materials

“…58 Recently, advances have been made by using ligand field density functional theory (LFDFT) to describe the 4f 7 good agreement. 59 Although useful, the computational cost of these calculations preclude HT computations from predicting the optical properties on a large scale.…”

Optical Absorption Spectra of Divalent Neodymium (Nd2+) in Bromide and Iodide Hosts

“…In recent years, spectroscopic properties of divalent lanthanide elements (Ln 2+ ) have been intensively studied, both experimentally and theoretically . However, electronic spectroscopy of divalent neodymium still remains practically an unexplored area.…”