K5Eu1- xTb x(MoO4)4 Phosphors for Solid-State Lighting Applications: Aperiodic Structures and the Tb3+ → Eu3+ Energy Transfer

Svetlana M Posokhova; Vladimir A Morozov; Dina V Deyneko; Ivan V Nikiforov; Boris S Redkin; Dmitry A Spassky; Alexei A Belik; Erzhena T Pavlova; Bogdan I Lazoryak

doi:10.1021/acs.inorgchem.2c00548

K₅Eu_{1- x}Tb _x(MoO₄)₄ Phosphors for Solid-State Lighting Applications: Aperiodic Structures and the Tb³⁺ → Eu³⁺ Energy Transfer

Inorg Chem. 2022 May 23;61(20):7910-7921. doi: 10.1021/acs.inorgchem.2c00548. Epub 2022 May 6.

Authors

Svetlana M Posokhova¹, Vladimir A Morozov¹, Dina V Deyneko¹, Ivan V Nikiforov¹, Boris S Redkin², Dmitry A Spassky^{3

4}, Alexei A Belik⁵, Erzhena T Pavlova⁶, Bogdan I Lazoryak¹

Affiliations

¹ Chemistry Department, Moscow State University, 119991 Moscow, Russia.
² Institute of Solid State Physics of Russian Academy of Sciences (ISSP RAS), 142432 Chernogolovka, Russia.
³ Skobeltsyn Institute of Nuclear Physics, Moscow State University, 119991 Moscow, Russia.
⁴ Institute of Physics, University of Tartu, W. Ostwald str. 1, 50411 Tartu, Estonia.
⁵ International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science, Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan.
⁶ Buryat State University, Smolin St. 24a, 670000 Ulan-Ude, Buryat Republic, Russia.

PMID: 35522973
DOI: 10.1021/acs.inorgchem.2c00548

Abstract

This paper describes the influence of sintering conditions and Eu³⁺/Tb³⁺ content on the structure and luminescent properties of K₅Eu_1-_xTb_x(MoO₄)₄ (KETMO). KETMO samples were synthesized under two different heating and cooling conditions. A K₅Tb(MoO₄)₄ (KTMO) colorless transparent single crystal was grown by the Czochralski technique. A continuous range of solid solutions with a trigonal palmierite-type structure (α-phase, space group R3̅m) were presented only for the high-temperature (HT or α-) KETMO (0 ≤ x ≤ 1) prepared at 1123 K followed by quenching to liquid nitrogen temperature. The reversibility of the β ↔ α phase transition for KTMO was revealed by a differential scanning calorimetry (DSC) study. The low-temperature (LT)LT-K₅Eu_0.6Tb_0.4(MoO₄)₄ structure was refined in the C2/m space group. Additional extra reflections besides the reflections of the basic palmierite-type R-subcell were present in synchrotron X-ray diffraction (XRD) patterns of LT-KTMO. LT-KTMO was refined as an incommensurately modulated structure with (3 + 1)D superspace group C2/m(0β0)00 and the modulation vector q = 0.684b*. The luminescent properties of KETMO prepared at different conditions were studied and related to their structures. The luminescence spectra of KTMO samples were represented by a group of narrow lines ascribed to ⁵D₄ → ⁷F_J (J = 3-6) Tb³⁺ transitions with the most intense emission line at 547 nm. The KTMO single crystal demonstrated the highest luminescence intensity, which was ∼20 times higher than that of LT-KTMO. The quantum yield λ_ex = 481 nm for the KTMO single crystal was measured as 50%. The intensity of the ⁵D₄ → ⁷F₅ Tb³⁺ transition increased with the increase of x from 0.2 to 1 for LT and HT-KETMO. Emission spectra of KETMO samples with x = 0.2-0.9 at λ_ex = 377 nm exhibited an intense red emission at ∼615 nm due to the ⁵D₀ → ⁷F₂ Eu³⁺ transition, thus indicating an efficient energy transfer from Tb³⁺ to Eu³⁺.