Wydział Chemii

Justyna Zeler

Megi Sulollari

Andries Meijerink

Marco Bettinelli

Eugeniusz Zych

2020

Journal of Alloys and Compounds

844

156096/1-156096/8

10.1016/j.jallcom.2020.156096

Naukowa

Angielski

Artykuł

The efficient 4f⁶5d→4f⁷ (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 ⁷F_J multiplets in the 4f⁶(⁷F_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 4f⁶(⁷F_J)5d electronic origins make these systems to be model compounds for testing the validity of theoretical models for energy level calculations of 4f⁶5d states of Eu²⁺.

Eu2+ luminescence, Vibronic progression, Lu/YPO4 crystals

http://dx.doi.org/10.1016/j.jallcom.2020.156096

http://www.elsevier.com