RESUMEN
Bi3+/Eu3+ doped Cs3GdGe3O9 luminescent materials were prepared by a solid-state reaction. The energy band and density of states of Cs3GdGe3O9 were calculated by density functional theory. The Cs3GdGe3O9 host presents a broadband emission peaking at 520 nm. Systemic measurement and analysis of luminescence properties were performed to confirm the energy transfer in Cs3GdGe3O9:Bi3+,Eu3+. The multicolor modulated emission from blue (0.1678, 0.1568) to red (0.5931, 0.3251) can be achieved by varying the doping ratio of bismuth to europium. A white light-emitting diode (WLED) was produced by combining the Cs3GdGe3O9:0.05Bi3+,0.1Eu3+ phosphor, a commercial green phosphor, and a 310 nm ultraviolet chip. The color rendering index of the WLED driven by 20 mA bias current is 89.6 with the CIE coordinates of (0.3520, 0.3626). The results reveal that the Cs3GdGe3O9:Bi3+,Eu3+ phosphor is a potential material that can be used in multicolor tunable luminescence and WLEDs.
RESUMEN
High-pressure structural searches of superhydrides CeBeH8and CeBH8were performed under ambient pressure up to 300 GPa. We identifyFm3â¾m-CeBeH8with a superconducting transition temperatureTcof 56 K at 10 GPa. Two more phases with spacegroupR3â¾mandC2/m, were investigated within the increasing pressures. CeBH8shows a similar phase transition process as CeBeH8but with higher transition pressures and higherTc.Fm3â¾m-CeBH8is predicted to be superconducting above 120 GPa with a maximumTcof 118 K at 150 GPa.R3â¾m-CeBH8andC2/m-CeBH8are dynamically stable above 120 GPa and 100 GPa, respectively. The maximumTcis 123 K at 195 GPa forR3â¾m-CeBH8, and 115 K at 350 GPa forC2/m-CeBH8. Our work enriches the family of ternary hydrides and may provide a useful guideline for further search for superconducting hydrides at low and moderate pressures.
RESUMEN
The photonic spin Hall effect (SHE), manifesting itself as spin-dependent splitting of light, holds potential applications in nano-photonic devices and precision metrology. However, the photonic SHE is generally weak, and therefore its enhancement is of great significance. In this paper, we propose a simple method for enhancing the photonic SHE of reflected light by taking advantage of the gradient-refractive-index (GRIN) material. The transverse shifts for a normal (homogeneous) layer and linear GRIN structure with three different types (singly increasing, singly decreasing, and doubly linear ones) are theoretically investigated. We found that the doubly linear GRIN materials exhibit the prominent photonic SHE of reflected light, which is mainly due to the Fabry-Perot resonance. By optimizing the thickness and the lower (higher) refractive index of the doubly linear GRIN layer, the transverse shift for a horizontally polarized incident beam can nearly reach its upper limitation (i.e., half of the beam waist). These findings provide us a potential method to enhance the photonic SHE, and therefore establish a strong foundation for developing spin-based photonic devices in the future.
RESUMEN
The thermal stability of the phosphors in phosphor-converted light-emitting diodes (LEDs) plays an important role in the practical application of lighting. Herein, the Mn2+-based red-emitting phosphors of pure and Eu2+-doped Sr9MnLi(PO4)7 (SMPO) samples were prepared using the high temperature solid-state reaction method. The crystal field environment around the Mn2+ ions was analyzed by combining the results of photoluminescence excitation spectroscopy and Tanabe-Sugano diagrams. By comparing the results of X-ray photoelectron spectroscopy, two additional bands centered at about 129.8 eV and 130.7 eV were found in the Eu2+-doped sample, which corresponded to the chemical states of P 2p3/2 and P 2p1/2. Two different sets of emission spectra were observed for Sr9MnLi(PO4)7:5%Eu2+ (SMPO:Eu2+) on employing the time-resolved technique. The emission peaks centered at 615 nm and 661 nm were attributed to Mn2+ and Eu2+ ions, respectively. The thermal quenching behaviors of Eu2+ and Mn2+ were investigated in the temperature range of 300-620 K and the thermal quenching mechanisms are given in this work. Systematic research on the luminescent properties of Eu2+ and Mn2+ ions in the SMPO:Eu2+ phosphor contributes to the understanding of the thermal stability and aids in the development of Mn2+-based red-emitting phosphors.
RESUMEN
Insulating ferromagnets with high T C are required for many new magnetic devices. More complexity arises when strongly correlated 3d ions coexist with strongly spin-orbit coupled 5d ones in a double perovskite. Here, we perform the structural, magnetic, and density functional theory (DFT) study of such double perovskite La2CuIrO6. A new P21/n polymorph is found according to the comprehensive analysis of x-ray, Raman scattering and phonon spectrum. The magnetization reveals a weak ferromagnetic (FM) transition at T C = 62 K and short range FM order in higher temperature range. A huge coercivity is found as high as H C ~ 11.96 kOe at 10 K, which, in combination with the negative trapped field, results in the magnetization reversal in the zero field cooling measurement. The first principle calculations confirm the observed FM state and suggest La2CuIrO6 of this polymorph is a Mott insulating ferromagnet assisted by the spin-orbit coupling.
RESUMEN
Recently, much attention has been paid to Mn4+-doped phosphors due to their strong deep-red emissions which are in demand in white light-emitting diodes. However, a key challenge for the commercialization of Mn4+-doped phosphors is their low thermal stability caused by the thermal quenching of Mn4+ luminescence. Herein, a strategy of optical temperature sensing has been developed by specifically utilizing thermal quenching to explore the potential applications of Mn4+-doped phosphors in optical temperature sensing. In this work, we report two kinds of double perovskite type phosphors, Ba2LaNbO6 (BLN) and Ca2LaNbO6 (CLN), co-doped with Mn4+ and Eu3+. Through the study of temperature-dependent spectra in a large temperature range of 298-498 K, Mn4+ and Eu3+ yield different trends where the fluorescence intensity of Mn4+ ions decreases much more rapidly compared to that of Eu3+ ions as the temperature increases. Accordingly, based on the fluorescence intensity ratio (FIR) of the luminescence of Mn4+ and Eu3+, the optimal relative sensitivity of temperature sensing in the BLN and CLN matrices could reach 2.08% K-1 and 1.51% K-1, respectively. Finally, the application potential of Mn4+-doped phosphors in temperature sensing is confirmed by analyzing different temperature sensing results in the two matrices.
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Monodisperse ß-NaYF4:1%Sm3+ nanoparticles were fabricated successfully via the thermal decomposition technique. Strong temperature dependence of the Sm3+ emission was observed when its thermally populated state H7/26 was directly excited to the G5/24 level. This strategy not only can eliminate laser heating and background Stokes-type scattering noise but also has a high quantum yield as a result of one-photon excitation process. Under 594.0 nm laser excitation, the emission intensity of G5/24-H5/26 enhances monotonously with rising temperature from 300 K to 430 K, including a physiological temperature range (27°C-60°C). The relative temperature sensitivity can reach 1.1% K-1 and 0.91% K-1 at 300 K and 330 K, respectively. In addition, the repeatability of temperature sensing was evaluated under several heating-cooling cycles, and the decay curves of the emission at 560.0 nm (G5/24-H5/26) at different temperatures were also investigated. These results raise the prospects of monodisperse ß-NaYF4:1%Sm3+ nanoparticles for optical temperature sensing in biomedicine fields.
RESUMEN
Cation doped Zn2GeO4 materials have been intensively explored owing to their excellent performance in photocatalysts, optoelectronic devices and white light-emitting diodes. However, the luminescence process and thermal quenching arising during the optical excitation of these materials are yet to be clarified. The pure and 2% Mn2+ doped Zn2GeO4 phosphors were prepared via the high temperature solid state reaction. The phosphors were characterized by X-ray diffraction, ultraviolet-visible diffuse reflectance spectroscopy, photoluminescence spectroscopy, X-ray photoelectron spectroscopy and afterglow decay curves. The thermal stability and quenching of Mn2+ luminescence were explained by the temperature dependence of photoluminescence spectroscopy and the configuration coordinate diagram. The thermal quenching of Mn2+ luminescence is mainly due to the delocalization of excited electrons from the excited state to the ionized state. Two kinds of origination of the O 1s peak were revealed by X-ray photoelectron spectroscopy. A model is constructed to interpret all the photoluminescence and long persistent luminescence of the Mn2+ doped Zn2GeO4. This may contribute to the understanding and optimization of luminescence properties for other Mn2+ doped inorganic phosphors.
RESUMEN
Rare-earth doped CaIn2O4 phosphors have been widely investigated due to their excellent luminescent property, but the site occupation of rare-earth ions in CaIn2O4 is not very clear and needs to be clarified. Using Eu3+ as a fluorescence probe, such a clarification has been made in this work. 1% and 2% Eu3+ doped CaIn2O4 powder samples have been prepared by the sol-gel method. The X-ray diffraction results indicate that the lanthanide doping does not influence the structure of CaIn2O4. Site selective excitation at low temperature disclosed five different luminescent centers marked as A, B, C1, C2 and C3. The spectral analysis revealed that the A and B sites belong to Eu3+ embedded in In3+ sites; the other three are attributed to Eu3+ substitution on Ca2+ sites, which show slight distortion. Energy transfers from the B site to the A and C1 sites were observed in the 2% Eu3+ doped CaIn2O4 sample. The transitions of Eu3+ ions in the Ca2+ sites make the main contribution to the emission spectra excited at room temperature. These results may provide a guide for optimizing rare-earth doped CaIn2O4 phosphors for their application in the solid state lighting field.
