Optical properties of Eu2+/Eu3+ mixed valence, silicon nitride based materials

Synthesis and Research of Rare Earth Nanocrystal Luminescent Properties for Security Labels Using the Electrohydrodynamic Printing Technique

YVO4:Eu3+ nanoparticles were successfully synthesized by two methods, namely the sonochemical method and hydrothermal method. The X-ray diffraction (XRD) patterns showed the tetragonal phase of YVO4 (JCPDS 17-0341) was indexed in the diffraction peaks of all samples. The samples synthesized by the sonochemical method had a highly crystalline structure (X-ray diffraction results) and luminescence intensity (photoluminescence results) than those synthesized by the hydrothermal method. According to the results of field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM), the average size of YVO4:Eu3+ nanoparticles was around 25–30 nm for the sonochemical method and 15–20 nm for the hydrothermal method. YVO4:Eu3+ nanoparticles in the case of the sonochemical method had a better crystalline structure and stronger emissivity at 618 nm. The Eu3+ ions’ average lifetime in YVO4:Eu3+ at 618 nm emission under 275 nm excitation were at 0.955 ms for the sonochemical method and 0.723 ms for the hydrothermal method. The security ink for inkjet devices contained YVO4:Eu3+ nanoparticles, the binding agent as polyethylene oxide or ethyl cellulose and other necessary solvents. The device used for security label printing was an inkjet printer with an electrohydrodynamic printing technique (EHD). In the 3D optical profilometer results, the width of the printed line was ~97–167 µm and the thickness at ~9.1–9.6 µm. The printed security label obtained a well-marked shape, with a size at 1.98 × 1.98 mm.

Insights into the complexity of the excited states of Eu-doped luminescent materials

Multiconfigurational ab initio embedded-cluster methods give a detailed view of the excited states of Eu-doped luminescent materials, improving the understanding of their structure and how it is affected by changing the host's chemical composition.

Characterization of Luminescent Materials with 151Eu Mössbauer Spectroscopy

The application of Mössbauer spectroscopy to luminescent materials is described. Many solids doped with europium are luminescent, i.e., when irradiated with light they emit light of a longer wavelength. These materials therefore have practical applications in tuning the light output of devices like light emitting diodes. The optical properties are very different for the two possible valence states Eu 2 + and Eu 3 + , the former producing ultraviolet/visible light that shifts from violet to red depending on the host and the latter red light, so it is important to have a knowledge of their behavior in a sample environment. Photoluminescence spectra cannot give a quantitative analysis of Eu 2 + and Eu 3 + ions. Mössbauer spectroscopy, however, is more powerful and gives a separate spectrum for each oxidation state enabling the relative amount present to be estimated. The oxidation state can be identified from its isomer shift which is between - 12 and - 15 mm/s for Eu 2 + compared to around 0 mm/s for Eu 3 + . Furthermore, within each oxidation state, there are changes depending on the ligands attached to the europium: the shift is more positive for increased covalency of the bonding ligand X, or Eu concentration, and decreases for increasing Eu⁻X bond length.

Optical properties of Eu2+ /Eu3+ mixed valence phosphor Ca2 SiO2 F2 :Eu2+ /Eu3

The Eu²⁺ /Eu³⁺ mixed valence phosphor Ca₂ SiO₂ F₂ :Eu²⁺ /Eu³⁺ was prepared using a solid-state reaction synthesis method in a CO atmosphere, and the optical properties were investigated. The spectroscopic properties revealed that Ca²⁺ ions were occupied by both Eu²⁺ and Eu³⁺ ions in Ca₂ SiO₂ F₂ , and both ions were able to generate their characteristic emissions. A broad 5d → 4f Eu²⁺ band at ~470 nm and narrow 4f → 4f Eu³⁺ peaks upon excitation with n-UV light were observed. The ratio between Eu²⁺ and Eu³⁺ emissions changed regularly, and the relative intensity of the red component from Eu³⁺ became systematically stronger with increasing overall Eu content. As a result, the emission color of these phosphors can be tunable from blue to pink under n-UV light excitation.

Low energy 4f-5d transitions in lanthanide doped CaLaSiN3 with low degree of cross-linking between SiN4 tetrahedra

CaLaSiN3 samples doped with Eu, Yb, Sm, Ce and Pr have been prepared via solid-state reaction synthesis and the optical properties have been studied. Both Yb and Sm were only observed in the trivalent state due to the fact that their Ln(2+) ground states are located inside or very close to the conduction band of the CaLaSiN3 host lattice. Doping with Ce(3+) or Eu(2+) resulted in a very low energy Ce(3+) or Eu(2+) 4f-5d absorption band around 1.9 eV (650 nm) and 1.4 eV (885 nm), respectively. The Ce(3+) 5d-4f emission appeared to be quenched, just as the Eu(2+) 5d-4f emission, which can be explained as the result of auto-ionization.