Optical Materials: X最新文献

Transition metal-activated phosphors belong to an important family of luminescent materials used as the next generation light sources for display, illumination systems, and other uses because of their small size, high luminescence efficacy, and long operation lifetime. Broad-band deep red or near infrared (NIR) emission has recently been observed in a wide variety of concentrated Mn⁴⁺, Mn²⁺, and Cr³⁺ phosphors as an additional anomalous emission band of the normal red or green emission band in such transition metal-activated phosphors. At present, the following two possibilities have been proposed as the cause of this anomalous broad emission band: (i) exchange-coupled transition-metal ion pair recombination and (ii) deep red or NIR-emitting traps activated by an efficient energy migration over the transition-metal sublattice to such trap centers. The present article presents current understanding of the anomalous deep red and NIR emission bands in highly Mn⁴⁺, Mn²⁺, and Cr³⁺-activated phosphors based on our current knowledge of the transition metal-activated phosphor physics.

Charge Transfer Luminescence (CTL) processes play a major roles in Yb:YAG laser materials act as a source of energy losses decrease the performance of this material. In this work, the temperature dependence of CTL in Yb:YAG single crystal was investigated. A 375-nm picosecond laser source was used as the excitation source. It was shown that the change in temperature affects the emission intensity and the position maximum of CTL occurring between perturbated F⁺ centers and Yb³⁺ ions. The increase in the temperature caused the blueshift of CTL, while the emission intensity have the inverted U-shape. The measured luminescence lifetime of CLT was in the range of 8 ns – 13 ns and barely changes with temperature. The temperature dependence of the CTL parameters was explained by the change in the energy transfer processes between F⁺ centers and the charge transfer state of Yb:YAG single crystals.

Transmission measurements in the 0.5–25-μm spectral range are performed on thin (<350-μm) GaAsP layers grown by Hydride Vapor Phase Epitaxy (HVPE) on plain (100) GaAs substrates. Comparison with calculations taking into account multiple reflections reveals the role of the surface polishing quality on the clear transmission window and the wavelength dependent losses. A measurement of a 5-mm thick epitaxially grown GaP underlines more realistic spectral limitations on the application of orientation-patterned structures based on GaP and GaAsP for nonlinear optical frequency conversion. The mid-IR cut-off wavelength for the ternary GaAsP layers is almost independent of the composition and corresponds to the same two-phonon absorption limit observed in the binary GaP. Nanohardness and Young's modulus are measured for the same samples to evaluate their compositional dependence. The nanohardness dependence on the P-content obeys a second order polynomial law with a maximum around P = 0.8. Young's modulus depends linearly on the P-content, similar to the trend observed in other ternary systems, such as In_xGa_1−xAs and In_xGa_1-xP. The evolution of the band-gap, estimated from the transmission measurements, with the composition of the ternary compounds is linear in the range of 0–0.5 for the P content. In this same range the nanohardness can be considered to be linearly proportional to the band-gap.

This article investigates the luminescent properties of olivine-type germanate ceramics luminophores doped with trivalent samarium (Sm³⁺) ions, prepared through a solid-state reaction method with two distinct compositions: Li₂MgGeO₄:0.5Sm³⁺ and Li₂ZnGeO₄:0.5Sm³⁺. The emission spectra for germanate systems displayed characteristic bands associated with Sm³⁺ ion transitions. The results obtained for the studied ceramic luminophores indicated that orangish-red and red emissions attributed to characteristic 4f-4f transitions of Sm³⁺ ions. On the other hand, broad bands assigned directly to the ceramic matrices were registered around 425 nm and 440 nm for Li₂MgGeO₄:0.5Sm³⁺ and Li₂ZnGeO₄:0.5Sm³⁺ samples, respectively. The impact of the matrix composition on the emission spectra of samarium-doped olivine-type germanate ceramics has been examined in details.

Scintillators are X-ray to visible light converters applied in X-ray imaging detectors used at synchrotrons. Drastically improved performances of the 4${}^{th}$ generation synchrotron sources enable us to perform X-ray imaging experiments at higher energies. For high spatial resolution X-ray imaging (micrometer to submicrometer), thin scintillating films are required. Consequently, especially for high X-ray energies (30 keV to 100 keV), the detection efficiency is limited due to the low X-ray absorption efficiency of the thin films. We have used Liquid Phase Epitaxy (LPE) to grow thin films of one of the ultimate high-density materials, Lu${}_2$Hf${}_2$O${}_7$:Eu${}^{3+}$, which demonstrate scintillating properties and thus combine high spatial resolution and maximized absorption efficiency. X-ray imaging experiments demonstrate that the Modulation Transfer Function (MTF) reaches 10% at 900 lp/mm, and radiographs visually confirm the promising imaging properties. We present structural, luminescent, and scintillation characterization of Lu${}_2$Hf${}_2$O${}_7$:Eu thin films grown on ZrO${}_2$:Y substrates, showing that the films crystallize in the disordered fluorite structure and the europium ions incorporate into the structure and enhance the luminescence intensity. This contribution is a first step toward developing promising ultra-dense, hafnate-based scintillating screens for high spatial resolution X-ray imaging.

Green fluorite samples from Homret Akarem, eastern desert Egypt, were investigated by laser-based Raman spectroscopy to study the effect of rare earth elements (REEs) and natural radiation from the surrounding environment on their physico-chemical properties, taking into consideration the geological setting. Geochemical data of trace elements display fluorite enrichment with Y, Pb, Sr, Sn, and other REEs. XRD showed lattice parameters with values higher than those for synthetic fluorite due to the substitution of Ca by Sr and less likely by radiation from U. A considerable shift in the binding energy (BE) for Ca and F obtained from the XPS spectrum indicates that U carried by the hydrothermal solutions formed a discontinuous thin film on the surface of fluorite. Laser-Raman spectroscopy showed strong peaks below 500 cm⁻¹ and both shallow and weak peaks above 500 cm⁻¹. The strong peaks indicate that the substitution of Ca by Sr, point defects, and natural radiation caused by U have a stronger effect on the crystal structure than REEs. Raman spectroscopy supported the initial reports of uranium minerals like Rutherfordine, Kasolite, Soddyite, and Uranophane-alpha.

The role of the addition of rare-earth ions which are Pr₂O₃, N₂O₃, Sm₂O₃, and Eu₂O₃ to Li₂O–ZnO–B₂O₃ glasses on the optical and radiation attenuation characteristics was theoretically investigated. According to the addition of the rare-earth ions, the glasses were named as LZB, LZBPr, LZBNd, LZBSm and LZBEu. The LZB glass has the greatest molar refractivity and the molar polarizability whereas LZBPr glass has the lowest molar refractivity and the molar polarizability. The reflection loss is the highest for the LZB and the optical transmission is the highest for LZBEu. Especially, at higher gamma-ray energy (5–15 MeV), the linear attenuation coefficients are the greatest for LZBPr and they are the lowest for LZB. The LZBPr has the lowest half value layer, tenth value layer and mean free path at 10 MeV gamma-ray energy. At higher gamma-ray energies, LZBPr has the better radiation protection efficiency. Consequently, the LZBPr glass has the superior radiation attenuation ability and the addition of rare-earth ions to LZB glass enhances radiation shielding ability of the studied glasses.

We studied the effect of Ga³⁺and Sc³⁺ on Yb:YAG emission at cryogenic temperatures on three different mixed garnets namely Yb:YGAG, Yb:YSAG and Yb:YSGAG. The compositional tuning of these mixed garnets was achieved by preparing ceramic pellets by solid state reaction with different concentration of Ga³⁺, or Sc³⁺, or both. The incorporation of Sc³⁺ in Yb:YAG leads only to a limited spectral broadening. On the other hand, the incorporation of either Ga³⁺ or both Ga³⁺ and Sc³⁺ results in a significant spectral broadening. In the latter case, this inhomogeneous broadening is attributed to the mixed occupancy of both Ga³⁺ and Sc³⁺ in octahedral and tetragonal sites in the crystal lattice leading to a significant distortion in the structure.

An effective performance enhancement model for the thin film solar cell conjointly based on extraordinary transmission and nanoantenna is proposed and investigated. The absorber layer of the extraordinary transmission based solar cell contains a metallic thin film with periodic holes. Maximum extraordinary transmission is accomplished as the metallic film has the same refractive index on both sides. Increased light transmission causes the absorber layer to absorb more light, which increases short circuit current density and subsequently the efficiency of the thin film solar cell. The presented analysis demonstrates that adding a square nano patch on the top surface of the absorber layer can further boost the extraordinary transmission. The extraordinary transmission is increased because of the formation of cavity nanoantenna. Cavity nanoantenna increases the coupling of light into the hole due to the excitation of surface plasmons polaritons. The proposed design of solar cell exhibits around 98% absorption and the short circuit current density is increased by a factor of 3.23. The study has been carried out using finite difference time domain (FDTD) method.

In this paper, the effect of Yb dopant on the optical and photoelectric properties of CsPbCl₃:Yb single crystals is studied. The position of the main energy level of Yb³⁺ ions relative to the energy band was determined. Two channels of electron photoionization into the conduction band were identified, which are photo-stimulated transition of valence electrons and transition of electrons from the ground level of the Yb³⁺ dopant ion. The crucial role of Yb²⁺ ions in the manifestation of the quantum cutting effect was shown. A non-uniform distribution of ytterbium dopant in the CsPbCl₃:Yb single crystal volume was revealed. It was established that the absolute quantum yield of ytterbium luminescence in CsPbCl₃:Yb single crystals in the near-infrared region at Yb concentration of 2 mol.% reaches 86%.