Lanthanide-Activated Phosphors Based on 4f-5d Optical Transitions: Theoretical and Experimental Aspects

Abstract

The synthesis of lanthanide-activated phosphors is pertinent to many emerging applications, ranging from high-resolution luminescence imaging to next-generation volumetric full-color display. In particular, the optical processes governed by the 4f-5d transitions of divalent and trivalent lanthanides have been the key to enabling precisely tuned color emission. The fundamental importance of lanthanide-activated phosphors for the physical and biomedical sciences has led to rapid development of novel synthetic methodologies and relevant tools that allow for probing the dynamics of energy transfer processes. Here, we review recent progress in developing methods for preparing lanthanide-activated phosphors, especially those featuring 4f-5d optical transitions. Particular attention will be devoted to two widely studied dopants, Ce and Eu. The nature of the 4f-5d transition is examined by combining phenomenological theories with quantum mechanical calculations. An emphasis is placed on the correlation of host crystal structures with the 5d-4f luminescence characteristics of lanthanides, including quantum yield, emission color, decay rate, and thermal quenching behavior. Several parameters, namely Debye temperature and dielectric constant of the host crystal, geometrical structure of coordination polyhedron around the luminescent center, and the accurate energies of 4f and 5d levels, as well as the position of 4f and 5d levels relative to the valence and conduction bands of the hosts, are addressed as basic criteria for high-throughput computational design of lanthanide-activated phosphors.

Single crystal growth, optical absorption and luminescence properties under VUV-UV synchrotron excitation of type III Ce3+:KGd(PO3)4, a promising scintillator material

“…The Stokes shift is induced by lattice relaxation at the excited states. Hence, the higher the value of Stokes shift is, the larger the relaxation of the electron at the excited state is before emitting electromagnetic radiation, resulting in higher non-radiative losses 39,40 . The Stokes shift is not dependent of the lanthanide ion, but only depends on the host.…”

Critical Review—Narrow-Band Emission of Nitride Phosphors for Light-Emitting Diodes: Perspectives and Opportunities

“…23b). 83 These models validate why hardly no existing trends can be derived from either host lattice rigidity or structural ordering of the lattice apart from the new set of cuboid phosphors and β-SiAlON, thereby serving as a direct and valid basis of narrow-band emission.…”

X-ray-activated long persistent phosphors featuring strong UVC afterglow emissions

“…We chose elpasolite Cs 2 NaYF 6 as the host and Pr 3+ ions as emitters with the ideas that (1) the Cs element has a strong X-ray absorption capability that makes the system capable of charging by X-ray irradiation, (2) Cs 2 NaYF 6 has a large bandgap and a propensity for the formation of structural defects that are likely to act as electron traps 32 , and (3) the 4 f 5 d –4 f 2 transition of Pr 3+ ions can result in UVC emission 29–31 . The micrometer-sized phosphor with a nominal composition of Cs 2 NaY (1 −x ) F 6 : x Pr 3+ was synthesized through a solid-state reaction method (Supplementary Fig.…”

“…Rare earth (RE) ions have been widely adopted as emitters in persistent phosphors owing to their intraconfigurational transitions. It is noted that some RE ions (e.g., Pr 3+ ) possess strong, high-energy, interconfigurational transitions, which thus could be employed as candidate emitters in UVC persistent phosphors 29–31 . The second required condition is the selection of the candidate host materials with a large bandgap and appropriate traps.…”