Effects of slight structural distortion on the luminescence performance in (Ca_1‐xEu_x)WO₄ luminescent materials

Abstract

(Ca1‐xEux)WO4 (x = 0–21 mol%) phosphors were prepared using the classical solid‐state reaction method. The influence of Eu3+ ion doping on lattice structure was observed using powder X‐ray diffraction and Fourier transform infrared spectroscopy. Furthermore, under this influence, the luminescence properties of all samples were analyzed. The results clearly illustrated that the element europium was successfully incorporated into the CaWO4 lattice with a scheelite structure in the form of a Eu3+ ion, which introduced a slight lattice distortion into the CaWO4 matrix. These lattice distortions had no effect on phase purity, but had regular effects on the intrinsic luminescence of the matrix and the f–f excitation transitions of Eu3+ activators. When the Eu3+ concentration was increased to 21 mol%, a local luminescence centre of [WO4]2− groups was detected in the matrix and manifested as the decay curves of [WO4]2− groups and luminescence changed from single exponential to double exponential fitting. Furthermore, the excitation transitions of Eu3+ between different energy levels (such as 7F0→5L6, 7F0→5D2) also produced interesting changes. Based on analysis of photoluminescence spectra and the chromaticity coordinates in this study, it could be verified that the nonreversing energy transfer of [WO4]2−→Eu3+ was efficient and incomplete.

Physicochemical Characterization of the Hybrid Molybdate–Tungstate Materials for Solid-State Lighting

“…The CT band of tungstate matrix CaWO 4 :1%Eu 3+ /1%Sm 3+ was observed in the spectral range from 200 to 300 nm with a maximum at about 260 nm, as an effect of electron transfer from 2p (O 2− ) to 5d (W 6+ ), and transitions from the ground state ( 1 A 1 ) to the high vibrational level of 1 B ( 1 T 2 ) within the WO 4 2− groups. 43,45,49 The concentration of Mo 6+ in the matrix structure shifting to longer wavelength 48 and the maximum in the excitation peak occurring at 300 nm (CT band extends to the range 200−350 nm) are possibly related to the further introduction of an intermediate energy level from the [MoO 4 ] cluster. This makes it possible to obtain more intense luminescence in a wider measuring range.…”

“…Suitable hosts for rare earth-based phosphors are known as borates, , alumina, molybdates, − niobates, ,, phosphates, − fluorides, ,− tungstates, − and so on. In the past few years, great attention has been focused on the molybdate–tungstate matrix ,− by virtue of its luminescence and structural properties.…”

Luminescence Characteristics of Dy3+/Eu3+ Doped CaBi2Ta2O9 Phosphors

“…12 Among these transitions, the 5 D 0 → 7 F 2 transition is an electric dipole transition and the emission band corresponding to this transition will be prominent while Eu 3+ ions locate in the sites without inversions. 13 Moreover, tunable luminescence was also found in Dy 3+ /Eu 3+ codoped phosphors due to the Dy 3+ → Eu 3+ energy transfers. 14,15 CaBi 2 Ta 2 O 9 is a type of mixed bismuth oxide layer material, which contains double TaO 6 octahedrons within the ( ) − CaTa O 2 7 2 perovskite blocks stacked between the (…”

Dy3+ → Eu3+ Energy Transfer in SrLaGa3O7:Dy3+/Eu3+ Phosphors

“…For example, erbium(III) (Er 3+ ), holmium(III) (Ho 3+ ) and thulium(III) (Tm 3+ ) are widely used as luminescence centers in up-conversion phosphors and ytterbium(III) (Yb 3+ ) can act as the sensitizer of these RE ions. 1 Cerium(III) (Ce 3+ ), 2 europium(II) (Eu 2+ ), 3 europium(III) (Eu 3+ ), 4 terbium(III) (Tb 3+ ), 5 dysprosium(III) (Dy 3+ ) 6 et al are widely used as luminescence centers in down-conversion phosphors and part of them can act as the sensitizers to improve the emission of the activators in sensitizer/activator codoped phosphors via the energy transfer processes. Up to now, some energy transfer processes have been reported, such as Ce 3+ → Eu 2+ , 7 Ce 3+ → Tb 3+ , 8 Tb 3+ → Eu 3+9 and Dy 3+ → Eu 3+ .…”