Halide Replacement with Complete Preservation of Crystal Lattice in Mixed‐Anion Lanthanide Oxyhalides

Abstract

Ac hallenge in anion control in periodic solids is to preserve the crystal lattice while substituting for different anions of widely varying sizea nd hardness.P ost-synthetic modification routes that place cations or anions in nonequilibrium configurations are promising;h owever,s uch methods remain relatively unexplored for anion placement. Here,w er eport the synthesis of LaOI nanocrystals by an onhydrolytic sol-gel condensation reaction and their transformation into LaOBr,LaOCl, and LaOF nanocrystals along hardsoft acid-base principles using post-synthetic metathesis reactions with ammonium halides.A nion displacement proceeds along halide planes,p reserving the tetragonal matlockite structure.E nergy-variant X-raye xcited optical luminesce signatures of alloyed Tb 3+ -ions is asensitive quantum reporter of the preservation of the cation sublattice and hardening of the crystal structure upon anion replacement.

Structure prediction via global energy landscape exploration of the ternary rare‐earth compound LaOI

“…showed evidence for enormous iodide anion migration in lanthanum oxyiodide‐based solids [10] . The most recent work reports the synthesis of LaOI nanocrystals by a non‐hydrolytic sol‐gel condensation reaction and their transformation into LaOBr, LaOCl, and LaOF nanocrystals using post‐synthetic metathesis reactions with ammonium halides [11] …”

The photoluminescence of isolated and paired Bi3+ ions in layered LnOCl crystals: a first-principles study

“…In this work, we select the layered and mixed-anion LnOCl (Ln = Y, Gd, La) hosts as prototype systems to study the photoluminescence mechanisms, i.e., the excited states involved, energies and relaxation processes, of isolated and paired Bi 3+ (6s 2 ) ions. The mixed-anion rare-earth oxyhalides LnOCl are important hosts for luminescent materials 27,28 and emerge as a family of effective van der Waals dielectrics 29 and Kitaev spin liquid candidates. 30 The photoluminescence of the Bi 3+ activator in a LnOX-type host, X being a halide ion, has been extensively studied in experiments.…”

Structure-Dependent Accessibility of Phonon-Coupled Radiative Relaxation Pathways Probed by X-ray-Excited Optical Luminescence

“…Panels A and B of Figure show normalized X-ray absorption near-edge structure (XANES) spectra of double and quadruple molybdates with different La/Dy ratios, respectively. Excitation across the La N 4,5 edge (95–150 eV), corresponding to a 4d → 4f core excitation, reveals characteristic absorption features arising from the excitation of the La 3+ singlet ground state to triplet 3 D 1 (dipole forbidden but observed because of spin–orbit coupling) and singlet 1 P 1 (dipole allowed) states. , The latter feature, labeled the giant resonance, has an anomalously high absorption cross-section stemming from strong 4d–4f overlap and exhibits asymmetric broadening as a result of the short lifetime of the excited state and the activation of non-radiative Auger emission pathways. − Spectral features appearing at ca. 106 and 108 eV are a result of exchange splitting caused by the overlap of 4d and 4f wave functions resulting in triakontadipole (Δ l = 5) and octupole (Δ l = 3) higher order multipole transitions upon 4d 10 4f n → 4d 9 4f n +1 core excitation (117 eV; Δ l = 1), respectively. , While these satellite bands are relatively low in intensity in the XANES spectrum, they can be clearly resolved in total-reflection inelastic X-ray scattering measurements …”

“…Optical luminescence arising from X-ray excitation of the lattice has been probed using X-ray-excited optical luminescence (XEOL) measurements. − Two-dimensional ­(2D) XEOL intensity maps in Figure S1A of the Supporting Information reveal the absence of visible emission features in NaLa­(MoO 4 ) 2 samples that do not incorporate Dy 3+ centers. In contrast, visible emission bands (most prominently, 4 F 9/2 → 6 H 15/2 at 480 nm and 4 F 9/2 → 6 H 13/2 at 570 nm) are observed in NaDy­(MoO 4 ) 2 only upon direct excitation at the Dy 3+ N 4,5 edge (ca.…”

“…It is well-established that 4 F 9/2 and 4 I 15/2 levels of Dy 3+ are thermally coupled and separated by an energy gap of ca. 1200 cm –1 . ,, The appearance of these emission features for double molybdate suggests that, upon excitation of La 4d core states, high-energy electron–hole pairs are thermalized and populate 4 I 15/2 levels of Dy 3+ centers on the rare-earth sublattice. , As such, La 3+ acts as a sensitizer and is coupled to the Dy 3+ chromophore through a phonon-mediated cross-relaxation pathway that populates excited 4 I 15/2 levels based on energy transfer across REO 8 polyhedra. ,, Notably, the phonon-assisted cross-relaxation pathway populating thermally excited states is accessible for the double molybdate but not the quadruple molybdate (Figure C and Figure S2B of the Supporting Information), delineating structure-dependent sensitization and coupling mechanisms. In other words, energy transfer between the crystal lattice and the color center is strongly dependent upon the connectivity of the polyhedra containing the La 3+ sensitizer and Dy 3+ emitter, which, in turn, is governed by the crystal structure and stoichiometry (Figure A).…”