Optical Materials: X最新文献

This work is devoted to examining the influence of energy transfer processes between Ce³⁺ and Pr³⁺ ions on the luminescent and scintillation properties of LuAG:Ce and LuAG:Ce,Pr scintillators, grown by liquid phase epitaxy onto undoped LuAG substrates with a PbO–B₂O₃-based flux. To characterize them, measurements of the absorption, cathodoluminescence, photoluminescence emission and excitation spectra as well as the photoluminescence decay kinetics of the SCFs under study were performed. The investigation confirmed simultaneous energy transfer processes between d-f and f-f states of Pr³⁺ ions and between Pr³⁺ (d-f) and Ce³⁺ (d-f) ions, as well as from Ce³⁺ (d-f) to Pr³⁺ (f-f) ions in LuAG host. Furthermore, the energy transfer from Pb²⁺ flux-related impurity to Ce³⁺ (d-f) and Pr³⁺ (f-f) ions also were found in the LuAG:Ce and LuAG:Ce,Pr SCFs. An energy diagram of the Pb²⁺, Pr³⁺ and Ce³⁺ ion levels was constructed, which provides a deeper overview of the mentioned energy transfer processes.

Plasma fluctuation dispersion has been theoretically and experimentally studied in monocrystal samples of Si (111) and Ge (111). It has been shown that the dispersion depends on crystallographic orientations of materials under study. In this work, the dispersion effects in the CLEE spectra, which manifest themselves in bulk samples of Si and Ge, have been studied. The loss energy electron was studied by the CLEE method upon their reflection from Si(111) and Ge(111) at different angles of incidence of the electron beam on the surface. Calculation of the total electron energy loss with formula (5) shows that the form of the CLEE spectrum of primary electrons depends on the nature and magnitude of the electron density in a given direction and is in satisfactory agreement with the experimental data. Thus, the theoretical and experimental results show that in the case of single-crystalline Si and Ge, with increasing k, the values of the bulk plasma oscillation increase by 2–3 eV.

The optical spectroscopy and the decay kinetics of samples with composition Sr₃Yb(PO₄)₃, Sr₃Y_0.98Yb_0.02(PO₄)₃, Sr₃Y_0.98Er_0.02(PO₄)₃ and Sr₃Yb_0.98Er_0.02(PO₄)₃ have been studied at room temperature. The presence of efficient energy transfer and migration processes has been clearly evidenced in the Sr₃Yb(PO₄)₃ and Sr₃Yb_0.98Er_0.02(PO₄)₃ materials, giving rise to strong visible upconversion upon excitation in the spectral region around 1 μm in the latter material. The strong anti-Stokes emission is connected to fast migration in the ²F_5/2 level of Yb³⁺, due to the inefficient concentration quenching for this ion. In this class of materials, the upconversion processes could be optimized even in the presence of high concentrations of the Yb³⁺ sensitizer.

K${}_2$YF${}_5$ crystals doped with lanthanide ions have a variety of possible optical applications. Owing to the low symmetry of the system, the crystal structure cannot be unambiguously determined by x-ray diffraction. However, electron-paramagnetic resonance studies have demonstrated that lanthanide ions substitute for yttrium in sites of C${}_s$ local symmetry. In this work, we use high-resolution absorption and laser spectroscopy to determine electronic energy levels for Er${}^{3+}$ ions in K${}_2$YF${}_5$ microparticles. A total of 39 crystal-field energy levels, distributed among 7 multiplets of the Er${}^{3+}$ ion, have been assigned. This optical data is used for crystal-field modelling of the electronic structure of Er${}^{3+}$ in K${}_2$YF${}_5$. Our model is fitted not only to the electronic energy levels, but also to the ground-state g-tensor. This magnetic-splitting data defines the axis system of the calculation, avoiding ambiguities associated with low-symmetry crystal-field fits.

A series of Lu₂O₃ single crystals doped with rare earth (RE) ions (RE = Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb, dopant concentrations are 1 %) was synthesized by the floating zone method. Their photoluminescence (PL) and scintillation properties were evaluated. In PL, emissions due to 4f-4f transitions of trivalent rare earth ions were observed, and those doped with Nd³⁺, Eu³⁺, Tb³⁺ and Er³⁺ showed the highest emission intensities among the samples. As a scintillation property, those doped with Eu, Gd, and Dy showed a clear photoabsorption peak under ¹³⁷Cs 662 keV γ-ray irradiation. Among them, the Eu³⁺-doped Lu₂O₃ showed the highest scintillation light yield of 67000 photons/MeV. The current work conducted the first systematic study of rare earth doped Lu₂O₃ single crystals grown by the floating zone method.

Scintillators with faster timing capabilities are currently in high demand for use in radiation detection systems in the fields of nuclear and medical physics. The limited number of suitable materials that meet the performance criteria of next generation detection systems presents an opportunity for discovery of new fast scintillator materials. In this work, the effects of doping several ultrafast core-valence luminescent (CVL) scintillators with divalent Zn is explored. Three compounds are investigated – CsMgCl₃, Cs₂MgCl₄, and Cs₃MgCl₅ – and single crystals of each doped with 5 mol% Zn are grown via the Bridgman method. Additionally, mixing across the full range of concentrations (from 0 % to 100 % Zn) is explored in the Cs₂Mg_1-xZn_xCl₄ and Cs₃Mg_1-xZn_xCl₅ systems. For low concentrations of Zn, light yields of all three compounds are enhanced (by up to ∼60 %) compared to the pure crystals, achieving what we believe to be the brightest known CVL, CsMgCl₃:Zn 5 % (3400 ± 170 ph/MeV light yield). More importantly, Zn doping does not affect the ultrafast timing properties, with each composition maintaining a single-component decay time around 1–3 ns. A sub-100 ps coincidence time resolution (CTR) is also achieved with CsMgCl₃:Zn 5 %. The results of this work reveal a new avenue towards obtaining brighter CVL materials, which could open up possibilities for more advanced ultrafast scintillators to be discovered moving forward.

Nitride-rich silicon-nitride (SiN${}_x$) is being explored for its potential as a suitable optical material for use in microsystems operating in the near-UV spectral range. Although silicon-rich SiN${}_x$ is widely accepted as a CMOS-compatible dielectric and micromechanical material, its optical absorption limits application to the visible to near-IR spectral range. However, this work shows that a balance can be achieved between a sufficiently high index of refraction ($n>$ 2) and an acceptable optical loss ($k<10^{-3}$) in nitride-rich SiN${}_x$ of appropriate composition ($x\sim 1.45$). Bragg reflectors with a design wavelength at ${\lambda }_o$= 330 nm are used for validation. PECVD is used for sample preparation and experiments confirm that the spectral range available for use of SiN${}_x$-based optical microsystems extends to wavelengths as low as 300 nm.

In this work, we investigate the opto-humidity sensing and colour tuning in polyvinyl alcohol (PVA) polymeric electrospun nanofibres dispersed with Tb(Sal)₃Phen (TSP) and Eu(DBM)₃Phen (EDP) complexes. Fourier transform infrared spectroscopy, scanning electron microscopy, and photoluminescence analysis were used to thoroughly analyse the structural, morphological, and spectroscopic features of the synthesised nanofibres in single and stacked multilayer nanofibres. A spectroscopic analysis was performed on all configuration schemes. Under UV excitations, the synthesised TSP complex and EDP complex inhibited nanofibres yield green and red emission corresponding to ⁵D₄→⁷F_j (j = 4, 5, 6) and ⁵D₀→⁷F_j (j = 0, 1, 2, 3) transitions attributed to Tb³⁺ and Eu³⁺ ions, respectively. The EDP nanofibres presented better UV radiation absorption than TSP, which was attributed to higher absorptivity of DBM than Sal. Additionally, the photoluminescence intensity ratio of characteristic emission peaks i.e. 544 nm (⁵D₄→⁷F₅)/615 nm (⁵D₀→⁷F₂) is function of humidity exposure and excitation wavelength. The stacked multilayer nanofibres exhibit good response and recovery times, 35 and 52 s, negligible hysteresis, and cyclic stability.

Sr₂MgTeO₆ (SMT) and Ba₂MgTeO₆ (BMT) ceramics with the double perovskite structure have been synthesized by solid-state route and by thermal decomposition of nitrate solution precursor. Both compounds possess interesting and unexpected emission properties in the visible and NIR regions, never reported before for this type of materials. These properties have been measured in different experimental conditions in order to characterize their nature. The literature information on tellurium containing luminescent materials is not rich and the data are somewhat contradictory: nevertheless, they agree in assigning the emission properties to Te⁴⁺ in octahedral coordination, whereas the Te⁶⁺ ion is considered not luminescent. The presence of Te⁴⁺ ions has then been verified by XPS measurements. On the basis of the experimental evidences, the visible luminescence has been assigned to a transition between the electronic levels of the Te⁴⁺ ion. The origin of the NIR emission appears more difficult to assess: among the explored hypotheses, the most convincing one, at the present level of the information, involves the possible interactions between the Te⁴⁺ and Te⁶⁺ ions with consequent formation of an optically active charge transfer state, as already observed for other ns²-type ions (Bi³⁺, Sb³⁺).

The demand for self-Q-switched lasers caused a growing interest in Cr⁴⁺:YAG materials. However, the main problem of Cr⁴⁺:YAG is an insufficient concentration of Cr⁴⁺ ions. This problem is complicated by the absence of the adequate model describing formation of Cr⁴⁺ ions. Analysis of the temperature dependence of Cr³⁺ luminescence in the Cr-doped YAG ceramics after different thermal treatments allows understanding the mechanism of Cr³⁺-Cr⁴⁺ valence transformation. Two types of Cr³⁺ centers with different spectroscopic properties were revealed in the Cr,Ca-doped YAG ceramics, namely, single Cr³⁺ ions, and Cr³⁺/ $\left[{\text{Ca}}_C^{\prime }\dots V_O^{·}\right]$ couples. Using the obtained spectroscopic data, a model of formation of Cr⁴⁺ ions in YAG lattice was proposed.