Pure and RE³⁺-Doped La₇O₆(VO₄)₃ (RE = Eu, Sm): Polymorphism Stability and Luminescence Properties of a New Oxyvanadate Matrix

Abstract

Two polytypes of the new oxyvanadate matrix La 7 O 6 (VO 4 ) 3 were identified and deeply characterized. The crystal structure of the α-polytype was solved using a combination of precession electron diffraction and powder X-ray diffraction (XRD) techniques. It crystallizes in a monoclinic unit cell with space group P2 1 , a = 13.0148(3) Å, b = 19.1566(5) Å, c = 7.0764(17) Å, and β = 99.87(1)°. Its structure is built upon [La 7 O 6 ] 9+ polycationic units at the origin of a porous 3D network, evidencing rectangular channels filled by isolated VO 4 tetrahedra. An in situ high-temperature XRD study highlights a number of complex phase transitions assorted with the existence of a β-polytype also refined in a monoclinic unit cell, space group P2 1 /n, a = 13.0713(4) Å, b = 18.1835(6) Å, c = 7.1382(2) Å, and β = 97.31(1)°. Thus, during the transitions, while the polycationic networks are almost identical, the vanadate's geometry is largely modified. The use of Eu 3+ and Sm 3+ at different concentrations in the host lattice is possible using solid-state techniques. The photoluminescence (PL), PL excitation (PLE) spectra, and luminescence decay times were recorded and discussed. The phosphors present an emission light, being bright and reddish orange after excitation under UV. This is mainly due to the V−O band and f−f transitions. Whatever the studied polytype, the final luminescence properties are retained during the heating/cooling process.

Samarium-Doped Metal Halide Perovskite Nanocrystals for Single-Component Electroluminescent White Light-Emitting Diodes

“…Moreover, four emission peaks centered at 565, 602, 645, and 710 nm can be observed in the doped PeNCs, which can be assigned to 4 G 5/2 to 6 H J ( J = 5/2, 7/2, 9/2, and 11/2) transitions of Sm 3+ ions, respectively. There is a broadening of Sm 3+ ion emission peaks in the spectra of doped PeNCs in comparison with the emissions from Sm 3+ ion-doped bulk crystals in the literature (Figure b), which results from a certain extent to size distribution as well as the large surface-to-volume ratio of PeNCs, inducing the complicated crystal field environments. − …”

A bacterial cellulose-based LiSrVO4:Eu3+ nanosensor platform for smartphone sensing of levodopa and dopamine: point-of-care diagnosis of Parkinson's disease

“… 25 Furthermore, an ionic complex group (VO 4 ) 3− , consisting of a vanadium ion coordinated to four O 2− ions in a tetrahedral symmetry, was found to be an effective luminescent center. 26 Vanadate compounds doped with rare-earth ions (Eu 3+ , Ho 3+ , Tm 3+ , Nd 3+ , Er 3+ , Pr 3+ , and Yb 3+ ) as phosphors emit various colors of light because of their high luminescence quantum yields. 27 These ions have narrow and parity-forbidden intraconfigurational 4fn ↔ 4fn transitions, which cause the emission of different light colors.…”

(3+1)-Dimensional Modulated Structure and Tb3+-Doped Luminescence for Vanadate Na3La(VO4)2

“…Vanadates are a group of the most important inorganic oxysalts with lower resultant temperature and the vanadate-based phosphors have been drawn more attention in the last 10 years, including such downconversion phosphors as La 7 O 6 (VO 4 ) 3 :RE 3+ (RE = Eu, Sm), Ca 3 Sr 3 (VO 4 ) 4 :Eu 3+ ,Al 3+ , and Ba 3 La­(VO 4 ) 3 :Eu 3+ and upconversion phosphors YVO 4 : Yb 3+ , Er 3+ , K 3 Y­(VO 4 ) 2 :Yb 3+ /Ln 3+ (Ln = Ho, Er, Tm), and Ca 5 Mg 4 (VO 4 ) 6 :Yb 3+ , Er 3+ . β-K 2 SO 4 is characterized by a very flexible structure, in which K can be substituted by other alkali metal atoms and the SO 4 group could be submitted by PO 4 to form various compounds. − In our previous studies, β-K 2 SO 4 -type phosphate Na 3 La­(PO 4 ) 2 was synthesized and single-crystal X-ray diffraction (SC-XRD) determination reveals that it crystallizes in the modulated structure with the super space group Pca 2 1 (0β0)­000 .…”