YVO4 Phosphors Research Articles

Hydrothermal Synthesis and Microstructural, Optical Properties Characterization of YVO4Phosphor Powder

The phonon energy of YVO4 crystal is lower than other usual compounds of salt. So it is suitable as host material for down-conversion materials. Hydrothermal method was adopted to synthesize YVO4 phosphor powder with the use of yttrium oxide and sodium vanadate as raw material. The change in the relative integral intensity of the (200) and (112) di raction peaks indicates that macroscopic stress in the lattice obviously changes with the elevated hydrothermal reaction temperature. The YVO4 phosphor powder synthesized involves a certain agglomeration of small particles. The phonon vibration in the YVO4 originates mainly from the internal vibrations in the vanadium oxygen tetrahedron, in addition to the Y O and O H vibrations. Due to a low phonon energy of only 2.8188 × 10−21 J, YVO4 helps to improve the down-conversion e ciency of rare-earth ions. A bandgap value of approximately 3.8 eV for the synthesized YVO4 powders leads to good absorption properties in the ultraviolet region. Upon excitation by the 320 nm ultraviolet photon, the intrinsic emission of YVO4 powders is annihilated, and a broadband emission of VO3− 4 near 450 nm is observed at room temperature. The YVO4 phosphor powder synthesized at 180 ◦C exhibits the maximum photoluminescence intensity because of its excellent crystallization.

Luminescent characteristics and energy transfer of a red-emitting YVO4:Sm3+, Eu3+ phosphor

Eu3+ and Sm3+ single-doped and co-doped YVO4 phosphors have been synthesized and their photoluminescence properties in the VUV–VIS region were investigated. Under the excitation of 405nm, the emission intensity of the optimal phosphor YVO4:Sm3+0.05,Eu3+0.05 at 619nm was largely enhanced compared to that of the sample without Sm3+, owing to the energy transfer from Sm3+ to Eu3+. The mechanism involved in this process has been explained and elucidated by an energy level diagram. While under the excitation of 147nm, the emission intensity of YVO4:Sm3+0.05,Eu3+0.05 at 619nm encounters a decreasing after the introducing of Sm3+ which is probably due to the competing of absorption energy of host between Sm3+ and Eu3+.

Bright white up-conversion emission from Er3+/Ho3+/Tm3+/Yb3+ co-doped YVO4 phosphors

Er3+/Ho3+/Yb3+/Tm3+ co-doped YVO4 phosphors were synthesized by the conventional solid-state reaction. Under 980nm laser diode excitation, intense red, green and blue up-conversion emissions were observed for the Yb3+/Er3+, Yb3+/Ho3+ and Yb3+/Tm3+ couples in the YVO4 host, respectively, which were due to the successive energy transfer from Yb3+ to Er3+, Ho3+ or Tm3+. Bright white luminescence upon 980nm near-infrared excitation can be observed for the sample at the optimum chemical composition of YVO4:10%Yb3+/1%Tm3+/0.3%Ho3+/0.2%Er3+. Under different excitation pump powers, the obtained optimal color coordinate (0.323, 0.325) is very close to the standard white light (0.333, 0.333) coordinate.

Strong luminescence enhancement of YVO4:Eu3+,Ba2+ phosphors prepared by a solvothermal method

It was known that Ba2+ doping can largely enhance the luminescence of lanthanide doped YVO4 phosphors. In this work, we employed a solvothermal method to prepare Eu3+,Ba2+ codoped YVO4 submicron-crystalline phosphors, and investigated the effect of Eu3+,Ba2+ codoping concentrations on the luminescence of the YVO4:Eu3+,Ba2+ phosphors. Both strong luminescence enhancement and quenching behaviors as a result of the Eu3+,Ba2+ codpoing have been observed in the YVO4:Eu3+,Ba2+ phosphors. It was found that Ba2+ dopants not only greatly enhanced the VO43- to Eu3+ charge transfer intensity, but also largely improved the 7F0,1→5L6 and 7F0,1→5D2 direct excitation intensity of the Eu3+ ions. Upon thermal annealing, an enormous enhancement in the luminescence has been observed for the YVO4:Eu3+,Ba2+ phosphors. The strong effects of Ba2+ dopants on the luminescence of both the as-prepared and the annealed YVO4:Eu3+,Ba2+ phosphors have been studied in detail. These results will provide a useful basis for further improving the luminescence performance of lanthanide doped YVO4 phosphors.

Efficient near-infrared quantum splitting in YVO4:Ho3+ for photovoltaics

A sequential two-step near-infrared (NIR) quantum splitting (QS) has been demonstrated in a Ho3+-doped YVO4 phosphor, whereby one incident ultraviolet (UV)-to-visible photon, enabling Ho3+:5F4,5S2 excited, could be split efficiently into two NIR photons with emissions at 1015 and 1190nm, respectively. The involved NIR-QS mechanism has been analyzed in terms of the static–dynamic photoemission, monitored excitation spectra and time-resolved emission spectra. Internal quantum yield is obtained up to 112% on the basis of experimental and theoretical calculation results. It is found that the broadband [VO4]3− group as a sensitizer could efficiently transfer its energy to Ho3+ activator ions, thus dramatically enhancing the UV photo-response and the NIR luminescence intensity of the phosphor. Further development of this two-step two-photon NIR-QS phosphor may open up a new approach for enhancing the photo-response of photovoltaic cells, particular in the wavelength range of 250–560nm.

Spectral conversion for solar cell efficiency enhancement using YVO4:Bi3+,Ln3+ (Ln = Dy, Er, Ho, Eu, Sm, and Yb) phosphors

Bi3+–Ln3+ (Ln = Dy, Er, Ho, Eu, and Sm) co-doped YVO4 phosphors are proposed as UV-absorbing luminescent converter candidate to enhance the power conversion efficiency and photochemical stability of dye-sensitized solar cells (DSSCs). The phosphors can efficiently convert UV photons in a broad range from 250 to 400 nm into visible emissions, which can be absorbed by DSSCs. Efficient broadband down-conversion UV light into near-infrared emission around 1000 nm was achieved in the YVO4:Bi3+,Yb3+ phosphors. The energy transfer from V5+–Bi3+ charge-transfer state to Yb3+ was shown to be a cooperative down-conversion type by the luminescence spectra, energy transfer efficiency, and luminescence decay curves. The YVO4:Bi3+,Yb3+ phosphors are promising for boosting the efficiency of crystalline silicon solar cells by down-converting the UV part of the solar spectrum to near-infrared photons with a twofold increase in the photon number. This research may open up promising new perspectives for designing novel luminescent materials for photovoltaic cells with high efficiency.

Methanol–Water System for Solvothermal Synthesis of YVO4:Eu with High Photoluminescent Intensity

A methanol–water mixed solvent was used as a reaction medium for the preparation of Eu3+‐doped YVO4 phosphor materials. These were synthesized by a solvothermal method at 150°–300°C using a 10 vol% solution of water in methanol as the reaction medium followed by calcination at 1000°–1200°C. The phase composition and optical properties of the products were characterized by X‐ray diffraction, scanning electron microscope, and photoluminescence spectroscopy. The powders obtained were composed of spherical particles ∼0.5 μm in size, with an internal structure that was different for samples prepared under subcritical and supercritical conditions of methanol. After the calcination, the powders obtained at 240°–300°C retained the initial raspberry‐like morphology, whereas the morphology of samples prepared at 150°–210°C changed significantly due to noticeable sintering. The fluorescence intensity exhibited by the prepared samples was higher than the fluorescence intensity shown by one of the best commercial YVO4:Eu phosphors having a large particle size.

Luminescent characteristics and morphology of Eu3+:YVO4 phosphor powders prepared by HCR and flux techniques

The emission intensities of Eu3+:YVO4 red phosphors depend significantly on the morphology and Y–V–O stoichiometry of powder particles. The low-temperature hydrolyzed colloid reaction (HCR) technique with different firing regimes in air and crystallization from lithium metavanadate (LiVO3) flux with subsequent grinding have been investigated. Powders reacted at the quasi-congruent (49.3 mol% V2O5–50.7 mol% Y2O3) composition and fired at temperatures up to 1200 °C exhibited higher emission intensities than the powders weighed at the stoichiometric (50 mol% V2O5–50 mol% Y2O3) ratio. After higher temperature (1400, 1600 °C) treatments the stoichiometric composition produces better luminescent properties approaching that of the highly optimized industrial powder standard (Sylvania 2391). Only limited emission was obtained for the crystalline powder prepared from LiVO3 flux due to the influence of mechanical grinding. Powder morphology and crystal structure were investigated by high-resolution transmission electron microscopy (TEM). The small particles produced at low temperature are surprisingly well crystallized with well resolved lattice images. The small particles contain internal surfaces as well as large external surfaces which contribute to the degradation of phosphor properties.