abstract
The efficient 4f(6)5d -> 4f(7) (d-f) luminescence from Eu2+ is well-known for host lattices where Eu2+ is substituted on a divalent (e.g. Ca2+, Sr2+) or monovalent (e.g. Na+, K+) cation site. Only recently some studies appeared concerning d-f emission from Eu2+ on a trivalent cation site. The stable Eu2+ emission was observed in X-ray irradiated LuPO4:Eu3+ crystals where Eu2+ is produced through trapping of conduction band electrons generated by X-ray absorption. Here, we demonstrated that Eu2+ can also be chemically stabilized in YPO4 and LuPO4 through co-doping with a tetravalent charge compensator: Hf4+. In orthophosphate crystals doubly doped with Eu and Hf, the characteristic Eu2+ emission is observed at low temperatures without the need for X-ray irradiation. The excitation and emission spectra show strong and narrow zero-phonon lines and a rich vibronic structure. In the excitation spectra a multitude of zero-phonon transitions to individual crystal field components of F-7(J) multiplets in the 4f(6)(F-7(J))5d excited state was observed for Eu2+ in both LuPO4 and YPO4. Analysis of the spectra is consistent with a slightly larger crystal field splitting for Eu2+ on the smaller Lu3+ site (compared to Y3+). The observation of many 4f(6)(F-7(J))5d electronic origins make these systems to be model compounds for testing the validity of theoretical models for energy level calculations of 4f(6)5d states of Eu2+. (C) 2020 Elsevier B.V. All rights reserved.
keywords
CATION SUBSTITUTION; VIBRONIC TRANSITIONS; CHARGE-TRANSFER; SOLID-SOLUTION; PHOSPHOR; EMISSION; IONS; SPECTRA; ENERGY; SPECTROSCOPY
subject category
Chemistry; Materials Science; Metallurgy & Metallurgical Engineering
authors
Zeler, J; Sulollari, M; Meijerink, A; Bettinelli, M; Zych, E
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