Synthesis and Properties of the La1 − x − y Eu y Ca x VO4 (0 ≤ x, y ≤ 0.2) Compounds

Abstract

The La1 − xCaxVO4 and La1 − x − yEuyCaxVO4 (0 ≤ x, y ≤ 0.2) micro/nanosized powders were prepared by aqueous nitrate–citrate sol–gel synthesis. Phase composition of the sample depends on the x and y values. The La0.9Ca0.1VO4 is crystallized in monoclinic structure up to the x = 0.1. The La0.9Eu0.05Ca0.05VO4 sample was also attributed to the monoclinic structure. Increasing concentration of europium and calcium ions in La1 − x − yEuyCaxVO4 solid solutions leads to the change of the crystal structure, and subsequently, stabilization of the tetragonal phase takes place.The obtained samples were characterized by XRD analysis, SEM microscopy, and IR spectroscopy. Luminescence properties of the synthesized powders were studied. Emission of the La1 − xCaxVO4 samples is weak and consists of wide bands in the 450–800 nm spectral range. The observed bands at 570 and 630 were ascribed to electron transitions in the distorted VO4 3− vanadate groups. Emission of the La1 − x − yEuyCaxVO4 samples consists of narrow spectral lines in the 550–730 nm spectral range. The lines are caused by the 5D0 → 7FJ electron transitions in the Eu3+ ions. The Ca2+ ions incorporation increases the intensity of the Eu3+ ions luminescence. Structure of the spectra depends on Ca2+ concentration and excitation wave length. The carried out analysis has revealed that Eu3+ ions form at least two different types of emission centers in the La1 − x − yEuyCaxVO4 samples. The assumption is made that type I centers are formed by the Eu3+ ions in their regular positions in the crystal lattice, while the type II centers have complex structure and consist of Eu3+ ions, Ca2+ cations, and oxygen vacancies.

Synthesis and Investigation of La,Ca ‐Doped EuVO4 Nanoparticles with Enhanced Excitation by Near Violet Light

“…The Eu 1− x Ca x VO 4 and La 1− x − y Eu y Ca x VO 4 samples with x, y = 0.05, 0.1, 0.15, and 0.20 were prepared by the aqueous nitrate–citrate sol–gel synthesis route using citric acid as a complexing agent according to procedure described in Ref. …”

“…Previous investigations have shown that partial replacements of the RE cations with iso‐ and heterovalent ions in the REVO 4 compounds lead to various changes of their physical and chemical characteristics . In particular, replacement of the RE cations with alkaline earth (AE) cations (Ca 2+ , Sr 2+ , Ba 2+ ) in the RE vanadate nanoparticles causes increase of luminescent intensity and arising of additional excitation band in violet spectral range of light …”

“…Spectral characteristics of this additional excitation band depend on material composition, concentration and type of the AE cations. Maxima positions were reported from 360 nm for Li 2 Ca 2 ScV 3 O 12 :0.15Eu 3+ , 380 nm for Zn 3 V 2 O 8 , 389 nm for Ca 2 KZn 2 (VO 4 ) 3 to 405 nm for La 1− x −y Eu y Ca x VO 4 . Nature of this excitation band is still under discussion.…”

“…Nature of this excitation band is still under discussion. It was ascribed to transitions in the vanadate groups, to presence of AE oxides impurity phases and to AE‐induced defects in the REVO 4 tetragonal phase . Mentioned excitation band is located in the range of the f‐f transitions in the Eu 3+ ions and it could be sometimes unrecognized in the spectra of the RE‐doped vanadates .…”

“…The La 1− x − y Eu y Ca x VO 4 nanoparticles were characterized by enhanced emission intensity, compared to La 1− x Eu x VO 4 , but they showed complicated structure of the luminescence spectra. So, the nature of mentioned enhancement, structural and spectral peculiarities is still under discussion . In order to clarify these issues we continued the study of the AE cations effects on REVO 4 compounds luminescence making synthesis of the Eu 1− x Ca x VO 4 (0 ≤ x ≤ 0.2) nanoparticles and studying their structural and luminescence properties.…”