Tuning morphology, surface, and nanocrystallinity of rare earth vanadates by one-pot colloidal conversion of hydroxycarbonates

Abstract

We show that particle size, morphology, nanocrystallinity, surface area, and defect density of (Y,Eu)VO4 structures can be tuned by one-pot colloidal conversion of rare earth hydroxycarbonates in water/ethylene glycol (EG)...

The Influence of Defects on the Luminescence of Trivalent Terbium in Nanocrystalline Yttrium Orthovanadate

“…The 5 D 4 decay curves (Figure k) fitted biexponential functions, confirming the occupation of multiple sites at surface and lattice, as also observed for other Ln 3+ ions in YVO 4 or different host lattices. , The 5 D 4 lifetimes decreased at higher Tb 3+ concentrations, in agreement with the Tb 3+ -Tb 3+ concentration quenching indicated by the emission spectra. Finally, literature reports that direct excitation in the 5 D 4 emitting state is ineffective in generating Tb 3+ luminescence in YVO 4 .…”

“…Comparison of absorption and emission spectra of undoped YVO 4 and Y 0.95 Tb 0.05 VO 4 samples provides additional insights on the effects of the annealing on the electronic structure of the particles (Figures S14–S15, Figure a). Undoped YVO 4 showed a red shift of the UV absorption edge, which is generally ascribed to V 4+ sites and lattice v O ·· defects. ,,,, Although the amount of V 4+ defects probed by XPS is approximately constant (Figure and Figure S6), the constriction of the unit cell favors more covalent V–O bonds, which culminates in a general decrease of the energy of the V-centered states. This is also consistent with the red shift of the 3 T 1,2 → 1 A 1 emissions of VO 4 3– in undoped YVO 4 with increasing annealing temperatures (Figure S15).…”

“…Luminescent rare-earth (RE) oxides have been extensively explored both in terms of theoretical detailing of 4f–4f transitions and for their unique applicability in lighting, visualization, nonlinear optics, and biolabeling technologies. − RE vanadates (REVO 4 ) are chemically stable and remarkably versatile hosts for lanthanoid (Ln) optical centers with downshift and upconversion emissions, which enable emerging applications in nanothermometry, sensing, and catalysis. − While Eu 3+ -doped YVO 4 is an ubiquitous UV-excited red phosphor, ,,, the inactivity of Tb 3+ -doped YVO 4 is an intriguing aspect in the chemistry and spectroscopy of vanadate-based luminescent materials. ,, During the search for efficient lamp phosphors in the late 1960s, many groups reported the complete absence of Tb 3+ luminescence in YVO 4 as well as the strong quenching of other Ln 3+ emissions induced by Tb 3+ -codoping. − Even though some groups studied Tb 3+ emissions in lanthanum (LaVO 4 ) − or gadolinium (GdVO 4 ) − vanadates, papers mentioning any luminescence in tetragonal YVO 4 :Tb 3+ are scarce, ,,, and no spectra or detailed characterization have been reported. The description of the Tb 3+ luminescence in AXO 4 zircon-type solids has been mainly performed for yttrium phosphates (YPO 4 ), phosphovanadates (YP 1– x V x O 4 ), and arsenovanadates (YAs 1– x V x O 4 ), which are isostructural to YVO 4 . ,− …”

“…In summary, annealing the Y 1– x Tb x VO 4 particles up to 500 °C in air induced two opposite trends concerning the density of defects. On the one hand, oxygen vacancies ( v O ·· ) are generated upon heating due to condensation of OH groups [2OH O · → O O x + v O ·· + H 2 O­(g)] or evolution of molecular O 2 [O O x → v O ·· ̈ + 2e′ + 1/2O 2 (g)], both compensated by reduced vanadium species (V V ′ ). Decomposition of CO 3 2– species into CO 2 (g) further generates oxygen ( v O ·· ) and vanadium ( v V ⁗ ) vacancies [i.e., C V ′ + 2O O x → 2 v O ·· + v V ⁗ + CO 2 ( g ), assuming carbonates occupy vanadate-like sites].…”

“…1−6 RE vanadates (REVO 4 ) are chemically stable and remarkably versatile hosts for lanthanoid (Ln) optical centers with downshift and upconversion emissions, which enable emerging applications in nanothermometry, sensing, and catalysis. 7−9 While Eu 3+ -doped YVO 4 is an ubiquitous UV-excited red phosphor, 1,5,6,9 the inactivity of Tb 3+ -doped YVO 4 is an intriguing aspect in the chemistry and spectroscopy of vanadate-based luminescent materials. 6,10,11 During the search for efficient lamp phosphors in the late 1960s, many groups reported the complete absence of Tb 3+ luminescence in YVO 4 as well as the strong quenching of other Ln 3+ emissions induced by Tb 3+ -codoping.…”