Preparation of cereal-like YVO(4):Ln(3+) (Ln = Sm, Eu, Tb, Dy) for high quantum efficiency photoluminescence

Optical transitions and radiative properties of green emitting Ho3+:YVO4 phosphor

The Ho³⁺-doped YVO₄ phosphors were successfully prepared via a sol-gel process in which citric acid was used as a chelating agent. X-ray diffraction (XRD) confirmed the effective inclusion of Ho³⁺ ions into the host matrix with the formation of single phase YVO₄. The surface morphology was observed using SEM, the results of which showed a grain growth propensity and the agglomeration of prepared phosphors. The V-O (VO₄ ^3-) vibration mode was analyzed through Fourier transform infrared (FTIR) spectra. The spectroscopic properties were reported through UV-vis-NIR diffuse reflectance and photoluminescence (PL) spectra. The Judd-Ofelt (J-O) intensity parameters Ω ₂ = 0.03 × 10^-20 cm², Ω ₄ = 0.22 × 10^-20 cm², and Ω ₆ = 0.23 × 10^-20 cm² obtained for the Y_0.97VO₄:0.03Ho³⁺ phosphors were used to obtain the total transition probabilities (A _T), radiative lifetimes (τ _rad) and branching ratios (β) for the certain transitions of Ho³⁺ ions. Under 310 nm UV excitation, the visible emission spectra were measured, and an intense emission was observed around 541 nm (green region) for all the samples. The emission cross-section σ _P(λ) was 3.22 × 10^-21 cm² and the branching ratio (β) was 0.816; these were investigated to capture the optimal concentration of the Y_0.97VO₄:0.03Ho³⁺ phosphor. The estimated color coordinates were observed in the green region of CIE diagram. Ultimately, the superior properties (σ _P(λ), β, and color purity) of Y_0.97VO₄:0.03Ho³⁺ phosphor may make it suitable for green emitting devices.

Generation of Pure Green Up-Conversion Luminescence in Er3+ Doped and Yb3+-Er3+ Co-Doped YVO4 Nanomaterials under 785 and 975 nm Excitation

Materials that generate pure, single-color emission are desirable in the development and manufacturing of modern optoelectronic devices. This work shows the possibility of generating pure, green up-conversion luminescence upon the excitation of Er3+-doped nanomaterials with a 785 nm NIR laser. The up-converting inorganic nanoluminophores YVO4: Er3+ and YVO4: Yb3+ and Er3+ were obtained using a hydrothermal method and subsequent calcination. The synthesized vanadate nanomaterials had a tetragonal structure and crystallized in the form of nearly spherical nanoparticles. Up-conversion emission spectra of the nanomaterials were measured using laser light sources with λex = 785 and 975 nm. Importantly, under the influence of the mentioned laser irradiation, the as-prepared samples exhibited bright green up-conversion luminescence that was visible to the naked eye. Depending on the dopant ions used and the selected excitation wavelengths, two (green) or three (green and red) bands originating from erbium ions appeared in the emission spectra. In this way, by changing the UC mechanisms, pure green luminescence of the material can be obtained. The proposed strategy, in combination with various single-doped UC nanomaterials activated with Er3+, might be beneficial for modern optoelectronics, such as light-emitting diodes with a rich color gamut for back-light display applications.

Crystal phase induced upconversion enhancement in Er3+/Yb3+ doped SrTiO3 ceramic and its temperature sensing studies

Through doping of Er³⁺/Yb³⁺ ions the SrTiO₃ perovskite ceramic is turned into an optically active material keeping its ferroelectric property intact. A huge enhancement of around 20 times in upconversion (UC) emission intensity is observed due to the transformation of cubic crystal structure to tetragonal phase. The intensity ratio of green to red band is found too high to neglect the contribution from the red emission band, which is not observed normally in such type of relatively moderate phonon frequency materials containing Yb³⁺/Er³⁺ ions. The change in emission intensity is reflected in the decay time measurement. Optical temperature sensing behavior based on FIR technique also has been discussed for Er³⁺/Yb³⁺ doped SrTiO₃ ceramic.

Synthesis characterization and luminescence studies of gamma irradiated nanocrystalline yttrium oxide

Nanocrystalline Y2O3 is synthesized by solution combustion technique using urea and glycine as fuels. X-ray diffraction (XRD) pattern of as prepared sample shows amorphous nature while annealed samples show cubic nature. The average crystallite size is calculated using Scherrer's formula and is found to be in the range 14-30 nm for samples synthesized using urea and 15-20 nm for samples synthesized using glycine respectively. Field emission scanning electron microscopy (FE-SEM) image of 1173 K annealed Y2O3 samples show well separated spherical shape particles and the average particle size is found to be in the range 28-35 nm. Fourier transformed infrared (FTIR) and Raman spectroscopy reveals a stretching of Y-O bond. Electron spin resonance (ESR) shows V(-) center, O2(-) and Y(2+) defects. A broad photoluminescence (PL) emission with peak at ~386nm is observed when the sample is excited with 252 nm. Thermoluminescence (TL) properties of γ-irradiated Y2O3 nanopowder are studied at a heating rate of 5 K s(-1). The samples prepared by using urea show a prominent and well resolved peak at ~383 K and a weak one at ~570 K. It is also found that TL glow peak intensity (I(m1)) at ~383 K increases with increase in γ-dose up to ~6.0 kGy and then decreases with increase in dose. However, glycine used Y2O3 shows a prominent TL glow with peaks at 396 K and 590 K. Among the fuels, urea used Y2O3 shows simple and well resolved TL glows. This might be due to fuel and hence particle size effect. The kinetic parameters are calculated by Chen's glow curve peak shape method and results are discussed in detail.

Incorporation of Zn(2+) ions into BaTiO3:Er(3+)/Yb(3+) nanophosphor: an effective way to enhance upconversion, defect luminescence and temperature sensing

Ferroelectric BaTiO3 became a multifunctional material via doping of lanthanide ions (0.3 mol% Er(3+)/3.0 mol% Yb(3+)) and subsequently upconversion luminescence was enhanced by incorporation of Zn(2+) ions. Upconversion luminescence of BaTiO3:Er(3+)/Yb(3+) perovskite nanophosphor has been studied using 800 and 980 nm laser excitations. The emission dynamics is studied with respect to its dependence on input power and external temperature including lifetime. Based on time-resolved spectroscopy, it is inferred that two types of Er(3+) sites are present in the barium titanate lattice. The first one is a short lived component (minor species) present at 6-coordinated Ti-sites of low symmetry while the second one is a long lived component (major species), present at 12-coordinated Ba-sites with high symmetry. The influence of the introduction of Zn(2+) ions on the lifetime of (4)S3/2 and (4)F9/2 levels of Er(3+) ions is also investigated. Enhanced temperature sensing performance (120 K to 505 K) of the material is observed using the fluorescence intensity ratio technique, employing the emission from the thermally coupled, (2)H11/2 and (4)S3/2 energy levels of Er(3+) ions. The defect luminescence of the material is also found to increase upon Zn-doping.

Bilayer stabilized Ln3+-doped CaMoO4 nanocrystals with high luminescence quantum efficiency and photocatalytic properties

In this article, we discuss the microwave synthesis of sodium dodecyl sulphate (SDS) stabilized Ln³⁺-doped CaMoO₄ nanocrystals (Ln³⁺ = Eu³⁺, Er³⁺/Yb³⁺).

Ligand-functionalization of BPEI-coated YVO4:Bi3+,Eu3+ nanophosphors for tumor-cell-targeted imaging applications

In this study, surface-functionalized, branched polyethylenimine (BPEI)-modified YVO4:Bi(3+),Eu(3+) nanocrystals (NCs) were successfully synthesized by a simple, rapid, solvent-free hydrothermal method. The BPEI-coated YVO4:Bi(3+),Eu(3+) NCs with high crystallinity show broad-band excitation in the λ=250 to 400 nm near-ultraviolet (NUV) region and exhibit a sharp-line emission band centered at λ=619 nm under excitation at λ=350 nm. The surface amino groups contributed by the capping agent, BPEI, not only improve the dispersibility and water/buffer stability of the BPEI-coated YVO4:Bi(3+),Eu(3+) NCs, but also provide a capability for specifically targeted biomolecule conjugation. Folic acid (FA) and epidermal growth factor (EGF) were further attached to the BPEI-coated YVO4:Bi(3+),Eu(3+) NCs and exhibited effective positioning of fluorescent NCs toward the targeted folate receptor overexpressed in HeLa cells or EGFR overexpressed in A431 cells with low cytotoxicity. These results demonstrate that the ligand-functionalized, BPEI-coated YVO4:Bi(3+),Eu(3+) NCs show great potential as a new-generation biological luminescent bioprobe for bioimaging applications. Moreover, the unique luminescence properties of BPEI-coated YVO4:Bi(3+),Eu(3+) NCs show potential to combine with a UVA photosensitizing drug to produce both detective and therapeutic effects for human skin cancer therapy.

Is BiPO4 a better luminescent host? Case study on doping and annealing effects

Metal phosphates have been popularly regarded as excellent luminescence hosts of lanthanide ions, while such an issue is challenged by the ignorance about the structural stability that may originate from the different chemical nature between the framework and the dopant lanthanide ions. Here, we choose BiPO(4) as a model compound to study. A detailed investigation of the effects of Eu doping and annealing on the structures and related luminescence properties of Bi(1-x)PO(4):Eu(x) (x = 0-0.199) has been carried out. A monoclinic phase (denoted as LTMP) was obtained for the undoped sample, which gradually transformed to a hexagonal phase (HP) with increasing doping level of Eu(3+) to x = 0.068. Further, it is also found that annealing had an obvious impact on the structures of the resulted samples. With increasing the annealing temperature up to 400 °C a phase transformation from HP to LTMP happens, which is opposite to that with doping. The above phase transformation behaviors were further confirmed by performing structural studies of doping with Dy(3+) ions and annealing undoped BiPO(4). The structural evolution had a great influence on the luminescent properties. Initially a significant decrease in Eu(3+) luminescence intensity and quantum efficiency was observed when LTMP transformed to HP. Afterward, a converse situation, increasingly enhanced luminescence performance, appeared when HP transformed to LTMP. Therefore, whether metal phosphates could be taken as better luminescence hosts must take into account their structural changes caused by the different chemical natures between framework and dopant ions, which may provide an important reference for designing new luminescent materials.