Inhomogeneous RVO₄ Photocatalyst Systems (R = Y, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu)

Abstract

By resorting on first-principles dynamical simulations and supporting experiments, we present a systematic and detailed inspection of a new series of inhomogeneous photocatalytic RVO4 systems (R = Y, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), where YVO4 is the most representative member. We evidenced a carrier separation, promoted by Pt acting as a cocatalyst, which allows for a clear understanding of the electronic properties of these inhomogeneous systems. These, in turn, are shown to be of crucial importance in enhancing the photocatalytic activity in the cases of water or methanol aqueous solutions. The presence of f electrons, acknowledged as essential for an optimal photocatalytic performance, is clearly rationalized and the possibility of using Lu, in view of its smaller ionic radius, to enhance hydrogen generation is disclosed. Experiments confirm that YVO4, GdVO4, and LuVO4 have a potentially much higher efficiency than compounds containing other rare earth lanthanides. Hence, we provide a comprehensive guideline for designing a new generation of photocatalysts possessing unprecedented efficiencies.

Pressure Effects on the Optical Properties of NdVO4

“…Interestingly, we found that after releasing pressure, our samples remain in the HP phase. This allows us to determine the band gap of the metastable monazite-type polymorph at ambient pressure, with E gap = 3.26 (2) eV. This value is probably more suitable for many photocatalytic applications than that of zircon-type NdVO 4 .…”

“…Trivalent metal orthovanadates have been constantly studied during the last decade because of their optical properties, which makes them appropriate for many different technological applications. Such applications go from photocatalytic water purification and hydrogen production to scintillators, phosphors, solid-state lasers, magnetoelectric, and medical applications [1][2][3][4][5][6]. Neodymium vanadate (NdVO 4 ) is one of the most promising orthovanadates for the development of technological applications [1][2][3][4][5][6], for which an accurate knowledge of NdVO 4 optical properties is a fundamental requisite.…”

“…Such applications go from photocatalytic water purification and hydrogen production to scintillators, phosphors, solid-state lasers, magnetoelectric, and medical applications [1][2][3][4][5][6]. Neodymium vanadate (NdVO 4 ) is one of the most promising orthovanadates for the development of technological applications [1][2][3][4][5][6], for which an accurate knowledge of NdVO 4 optical properties is a fundamental requisite. Several studies have been carried out on the optical properties of NdVO 4 [6][7][8][9][10][11], mainly focused on the study of the band-gap energy and the optical absorptions associated to internal transitions of Nd 3+ ions from 4 I 9/2 to 4 G 5/2 , 4 F 7/2 , 4 F 5/2 , and 4 F 3/2 [12].…”

Theoretical studies of the dependence of EPR parameters on local structure for the tetragonal Er3+ centres in YVO4 and ScVO4

“…For instance, the EPR g-factors, g // = 3.544, g \ = 7.085 for the Er 3+ in the YVO 4 crystal, and the g // =6.35, g \ = 4.53 for the Er 3+ in ScVO 4 crystal, indicate the opposite anisotropy of the g-factors [22,23]. (2) As to the two systems, the lowest states have been attributed to the Kramers doublet 2 C 6 from the EPR parameters, which imply the rule that the average g-tensor g av (= |g // |/3 + 2|g \ |/3) of the tetragonal Er 3+ centres in the YVO 4 and ScVO 4 will be close to the theoretical value g av (g av % 5.976)…”

“…Introduction Trivalent rare-earth (RE) ions doped in vanadates have received considerable attention because of the wide applications such as in phosphors, display monitors, X-ray imaging, lasers, and amplifiers for fiber-optic communication [1][2][3][4][5][6][7][8][9][10][11]. For instance, Eu 3+ -ion activated YVO 4 can be utilized as a red phosphor in a cathode ray tube (CRT), and as a scintillator in medical image detector [3][4][5][6][7][8].…”