Strong Visible and Near-Infrared Cathodoluminescence in Alkali Feldspar

In this study, cathodoluminescence (CL) spectroscopy at direct current and alternating current under the sample temperature condition of 40–293 K using different modulation frequencies is presented for alkali feldspar from the Dartmoor granite (UK). These feldspars contain strain-controlled lamellar crypto- and microperthites that are cross-cut by strain-free deuteric microperthites. The CL spectra of the alkali feldspar at room and low temperature confirm that the observed emission peaked at ～460 nm could be associated with Al-O^?-Al or Ti impurity centers, yellow emission ～560 nm could be associated with the presence of the centers such as radiation-induced defect centers, and ～756 nm emission could be associated with the Fe³⁺ impurity center on T₁ and T₂ sites. The consequence of their association is to produce different luminescence properties such as intensity, peak wavelength, and band shape.     

High pressure and emission spectra of Eu3+ in L-EuBO3

Effects of the high pressure on the emission spectra of Eu³⁺-activated L-EuBO₃ were considered at room temperature up to 100 kbar. The position of five 0–2 lines in the ⁵D₀→⁷F₂ transition region was determined. The pressure does not have the same effect on all these lines. In four of them, high pressure induced a red shift with different shift rates:+0.0022,+0.0035,+0.0034 and+0.0027 nm kbar^?1, respectively, whereas in the last one, high pressure induced a blue shift with shift rate?0.0034 nm kbar^?1. Possible reasons for the mentioned pressure effects on the line positions were considered.     

Multicolor upconversion emission from Tm3++Ho3++Yb3+ codoped tellurite glass on NIR excitations

Multicolor emission has been produced using 798 nm and 980  nm laser excitation in a Tm³⁺+Ho³⁺+Yb³⁺ codoped tellurite based glass. This glass generates simultaneously red, green and blue (RGB) emission on 798 nm excitation. Multicolor emission thus obtained was tuned to white luminescence by adjusting the Ho³⁺ ion concentration. There is a close match between the calculated color coordinate for the white luminescence obtained here and the point of equal energy which represents white in the 1931 CIE chromaticity diagram. The 980 nm excitation of the same sample on the other hand gives intense green and red emission and the glass appears greenish.     

Preparation and characterization of upconversion luminescent Tm3+/Yb3+ co-doped Y2O3 nanophosphor

Tm³⁺/Yb³⁺ co-doped Y₂O₃ nanophosphor has been synthesized by the solution combustion technique. Heat treatment of the phosphor materials at higher temperatures modifies the structural and optical properties. At low concentration of Yb³⁺, an intense upconversion emission is observed in blue region (478?nm) on excitation with 976?nm radiations. Emission has also been observed in the ultraviolet (UV) region viz. at 300?nm. The intensity of blue emission initially increases with dopant concentration as well as with the annealing temperature. However, for higher concentrations of Yb³⁺ (10?mol%), emission in the blue region is greatly suppressed and NIR emission at 813?nm appears with a large intensity. Intensity ratio of NIR and blue emission (I _NIR/I _B) reaches 74, resulting in almost monochromatic light at 813?nm. To check the suitability of blue emission for display devices, CIE color coordinates (x,y), color purity and the dominant wavelength (?? _d) for the blue emission have been calculated and the resulting value is found to be close to the coordinates of available standard blue phosphors.     

Green,blue, red,near-infrared up-conversion luminescence of Yb<Superscript>3+</Superscript>/Er<Superscript>3+</Superscript>/Tm<Superscript>3+</Superscript> co-doped YVO<Subscript>4</Subscript> nanoparticles

YVO₄:Yb³⁺,Er³⁺; YVO₄:Yb³⁺,Tm³⁺; and YVO₄:Yb³⁺,Er³⁺,Tm³⁺ were all synthesized via sol-gel method with a subsequent thermal treatment. Specifically, YVO₄:Yb³⁺,Er³⁺,Tm³⁺ phosphors were prepared with different annealing temperatures to study the influence of temperature. The transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray diffractometer (XRD), and photoluminescent (PL) spectrofluorometer were used to investigate the morphology, crystal structure, and up-conversion luminescent properties of all samples. In summary, all samples were granular-like nanoparticles and well crystallized with the same tetragonal phase as YVO₄. Under the irradiation at 980 nm, YVO₄:Yb³⁺,Er³⁺ phosphors can generate green emission at 525 and 553 nm and red emission at 657 nm, while YVO₄:Yb³⁺,Tm³⁺ phosphors can generate blue emission at 476 nm, red emission at 648 nm, and near-infrared emission at 800 nm. Notably, YVO₄:Yb³⁺,Er³⁺,Tm³⁺ samples can exhibit green emission, blue emission, red emission, and near-infrared emission at the same time, which might endow the as-prepared samples with potential applications in many fields, such as luminous paint, infrared detection, and biological label.     

Manifestation of up-conversion in Yb3+/Tm3+ doped Li2O–Y2O3–SiO2 glass system

In this study, we have investigated the principal role of Y₂O₃ on the emission features of Tm³⁺ ion and up-conversion phenomenon in Tm³⁺ and Yb³⁺ co-doped Li₂O–Y₂O₃–SiO₂ glass system. The concentration of Y₂O₃ is varied from 0 to 5 mol% while that of Yb³⁺ and Tm³⁺ is fixed. When the glasses are doped with Tm³⁺ ions, the intense blue and red emissions were observed, whereas Yb³⁺ doped glasses exhibited NIR emission at about 980 nm. When the glasses are co-doped with Tm³⁺ and Yb³⁺ ions and excited at 900 nm, the blue and red emission lines were observed to be reinforced and strengthened with increase in the concentration of Y₂O₃. The IR emission band detected at about 1.8 μm due to ³F₄ → ³H₆ transition of Tm³⁺ ions is also observed to be strengthened due to co-doping. The reasons for enhancement in the intensity of various emission bands due to co-doping have been identified and discussed with the help of rate equations for various emission transitions.     

Assessment of role of iron ions on the physical and spectroscopic properties of multi-component Na2O−PbO−Bi2O3−SiO2 glass ceramics

Multi-component glass ceramics composition Na₂O?PbO?Bi₂O₃?SiO₂ doped with different concentrations of Fe₂O₃ as nucleating agent were characterised by XRD, SEM (scanning electron microscope) and DTA (differential thermal analysis) techniques. Optical absorption, EPR, FTIR and Raman studies are also carried out on these glass ceramics. Absorption bands observed at about 457, 489, 678 and 820 nm are the characteristics of Fe³⁺ ions whereas the band observed at about 964 nm is due to Fe²⁺ ions. EPR studies suggested that Fe³⁺ ions entered in the lattice as tetragonally distorted octahedral symmetry or rhombic sites at low concentration of Fe₂O₃, whereas at higher concentration of Fe₂O₃ (beyond 1 mol%), the super exchange type of interactions between multivalency iron ions begin to dominate. FTIR and Raman spectra have revealed the behaviour of various structural units in the glass ceramic matrix. The analysis of these spectroscopic studies indicates that iron ions do exist in Fe³⁺ and Fe²⁺ state.     

Spectroscopy of Nickel-Doped Zinc Sulfide Nanoparticles

ABSTRACT

In the present study, Zn_1?xNi_xS (x = 0.0–0.8 mol%) nanoparticles were prepared through the chemical route and the synthesis involved the mixing and drying of zinc acetate and sodium sulphide in an appropriate ratio with the addition of Ni²⁺ at a proper concentration. The structural and spectroscopic studies are investigated by X-ray diffraction (XRD), absorption spectra, emission and excitation spectra, and Raman spectra. Compared with that of the pristine materials, the absorption band-edge demonstrates an apparently blue shift, which is attributed to the quantum size effect. The average particle size of ZnS nanoparticles is in the range of 2–4 nm deduced from the XRD line broadening. Excited at about 330 nm, a blue emission band at 425 nm can be observed, which corresponds to Ni²⁺ luminescent center; this result is consistent with the postulation that Ni²⁺ replaced the Zn²⁺ ions in the lattice of ZnS nanocrystals. Excitation spectra also confirm the above postulation. The effect of different concentrations of nickel is also studied by Raman spectra.     

Cytotoxicity and inflammation in human alveolar epithelial cells following exposure to occupational levels of gold and silver nanoparticles

This study explores the viability of rare earth-doped zirconia nanophosphors as probable candidates for white light emission. Undoped ZrO₂ and single- and double-doped ZrO₂:M (where M?=?Tb³⁺ and Eu³⁺) nanophosphors have been synthesized using a simple sonochemical process. The products were characterized using X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDS), and photoluminescence spectrophotometry. The SEM micrographs show that resultant nanoparticles have dendritic shape. TEM and HRTEM studies showed that the size of the majority of the nanoparticles were around 28?±?5?nm. Characteristic blue and green emission from Tb³⁺ ions and red from Eu³⁺ dopant ions were observed. The CIE coordinates of the double-doped ZrO₂:Tb³⁺ (1.2?%):Eu³⁺ (0.8?%) nanophosphor lie in the white light region of the chromaticity diagram and show promise as good phosphor materials for new lighting devices.     

Luminescence of Strontianite (SrCO3) from Strontian (Scotland, UK)

An historic Strontianite-type specimen from Strontian, Scotland, UK, was characterized to broaden our knowledge on luminescence properties of common carbonates. These fibrous aggregates are Strontianite (Sr_xCa_1−xCO₃) with circa 6% of CaO, interfacial water, hydrosilicate anions and substitutional divalent cations, e.g., Ca²⁺, Mn²⁺, Fe²⁺ in structural Sr²⁺ positions. The specimen was analyzed by X-ray Fluorescence Spectrometry (XRF), Environmental Scanning Electron Microscopy coupled with an Energy Dispersive X-ray Spectroscopy (ESEM-EDS) probe, Spatially-resolved Cathodoluminescence under the Scanning Electron Microscope (SEM-CL), Differential-Thermal Analyses (DTA), Thermogravimetry (TG), Thermoluminescence (TL), Radioluminescence (RL) and High Resolution Spectra Thermoluminescence (3DTL), to gain an overview of the spectral emissions, the defect linkages were modified by heating from room temperature (RT) up to 500 °C. Substitutional transition elements are probably responsible for the spectral emission bands from 500 nm to 800 nm and hydrous molecules from 300 nm to 400 nm. DTA–TG analyses performed on little chips, to preserve the fiber interfaces coherence, exhibit minor endothermic peaks attributed to outflow of water groups in fiber interfaces. Both, CL and RL curves show common spectral positions but UV–blue and red emission intensities are counterbalanced since electron irradiation reduces the UV–blue emissions while X-irradiation increases them. The TL curves show a top thermal limit at 300 °C for the 300–400 nm TL emissions which become irreversibly destroyed, whereas the longer wavelength region emits at higher temperature. The non-reversible changes observed in the 320 nm and 360 nm bands during the spectra 3DTL emission could be linked with non-bridging oxygen defects, protons and hydroxyl groups and the red emissions to the ⁴G (⁴T_1g)–⁶S Mn²⁺ ion transition. Following assignations and similar spectral CL patterns of Russian Strontianite samples, the emission-defect assignments: Dy³⁺ 480 nm; Tb³⁺ 540 nm; Dy³⁺ 580 nm and Sm³⁺ 640 nm cannot be disregarded.     

Near-infrared quantum cutting via resonant energy transfer from?Pr3+ to Yb3+ in LaF3

Experimental evidence of energy transfer from Pr³⁺ to Yb³⁺ were presented by the excitation spectra and emission spectra in LaF₃:Pr³⁺,Yb³⁺. Temperature-dependent infrared emission and fluorescence decay curves have been measured to investigate the quantum cutting mechanism and energy transfer efficiency of the Pr³⁺?CYb³⁺ couple. Upon excitation of Pr³⁺ at 442?nm, Yb³⁺ emits two near-infrared photons around 1000?nm through two resonant energy transfer processes from Pr³⁺ to Yb³⁺ and the maximum total quantum efficiency reaches 161.6%. The excellent luminescence properties of the Pr³⁺?CYb³⁺ codoped LaF₃ indicate its potential application in improving the energy conversion efficiency of the silicon based solar cells by converting one blue photon to two near-infrared ones.     

SrAl4O7:Tm3+/Yb3+ nanocrystalline blue phosphor: structural, thermal and optical properties

Strontium aluminate (SrAl₄O₇) nanophosphor codoped with Tm³⁺–Yb³⁺ has been synthesized through the combustion route using urea as the reducing agent. Structural, thermal and optical characterizations have been carried out. Heat treatment of the samples shows a change in the crystallite phases and the relative luminescence intensities for the different bands. The nanocrystalline particles in the as-synthesized sample seem to arrange in rod like shapes of submicrometer length on annealing. A broad (350–550 nm) emission in the UV–green region is observed when 266 nm radiation is used for excitation. Intense upconversion (UC) emissions in blue, red and infrared are seen with excitation by 976 nm radiation. An emission at 364 nm not observed earlier and attributed to ¹D₂→³H₆ transition in Tm³⁺ is also seen. The blue emission from SrAl₄O₇:Tm³⁺/Yb³⁺ codoped nanophosphor (annealed at 1200°C) exhibits high color purity (89%) and is comparable to phosphors used commercially. The energy transfer mechanisms, responsible for these UC emissions, are proposed and discussed.     

Probing luminescence centers in Na rich feldspar

In contrast to the detailed investigations on the dosimetric electron trap in feldspar only little has been done to understand the luminescence centers. We use a comparison of multiple spectroscopic techniques, site selective photoluminescence spectroscopy and time resolved measurements to further our understanding of the luminescence mechanisms and recombination sites, in a sample of Na rich plagioclase feldspar (oligoclase). Both the UV and violet–blue emissions show resonant excitations arising from a distribution of energy levels. We propose, contrary to the general understanding, that the green emission may not arise from Mn²⁺ in our sample and that photoionisation of this centre may be possible by excitation to the band tail states. The deep red emission is tied to the Fe³⁺, and the exponential rise in the UV excitation efficiency of this centre is discussed in the context of the band-tail model.     

Spectroscopic Studies of a New Multi-Element Sensitive Fluorescent Probe Derived from 2-(2-pyridyl)benzimidazole: Selective Discrimination of Zn2+ from Its Congeners

ABSTRACT

A new multielement sensitive fluorescent probe, 1-(2-(phenylthio)ethyl)-2-(pyridin-2-yl)-1H-benzo[d]imidazole (L), has been synthesized by the reaction between 2-(pyridyl) benzimidazole and 2-chloroethyl phenyl sulfide. Excitation and emission wavelength of L are at 330 and 371 nm, respectively. Among various transition and nontransition metal ions, it can selectively read Zn²⁺ ion as the emission wavelength of L undergoes a red shift by 31 nm upon binding with Zn²⁺ in methanol. In the presence of Cd²⁺, Hg²⁺, and other common cations, the emission wavelength of L remains unchanged, and thus allows us to discriminate Zn²⁺ from its congeners. Both L and its Zn²⁺ complex are well characterized by different spectroscopic techniques like ¹H-NMR, ESI-TOF (+) mass, FT-IR, and elemental analysis data. The binding constant value of the complexation reaction between L and Zn²⁺ is found as 724.6 M^?1 in methanol. Density functional theoretical (DFT) studies nicely demonstrate the red shift in the emission wavelength of L upon binding with Zn^2+.     

发光二极管用SrWO4:Eu3+红光荧光粉激发谱强度的调控

采用化学共沉淀法制备了Eu³⁺掺杂摩尔分数不同、煅烧温度不同的SrWO₄:Eu³⁺系列发光粉体, 所制备的粉体均具有Eu³⁺特征的强室温红光荧光发射. 通过调节煅烧温度和掺杂摩尔分数来调控近紫外和蓝光吸收强度, 进而调控用395 nm的近紫外光和465 nm的蓝光激发样品所得红光发光强度. 研究结果表明, 所制备的SrWO₄:Eu³⁺红光荧光粉可以被紫外和蓝光发光二极管有效激 关键词： 稀土掺杂 4:Eu³⁺')" href="#">SrWO₄:Eu³⁺ 光致发光 白光发光二极管     

Low-voltage cathodoluminescence property of Li-doped Gd2−xYxO3:Eu

Cathodoluminescent (CL) spectra of Li-doped Gd_2−xY_xO₃:Eu³⁺ solid-solution (0.0?x?0.8) were investigated at low voltages (300 V-1 kV). The CL intensity is maximum for the composition of x=0.2 and gradually reduces with increasing the amount of substituted Y content. In particular, small (∼100 nm) particles of Li-doped Gd_1.8Y_0.2O₃:Eu³⁺ are obtained by firing the citrate precursors at only 650°C for 18 h. Relative red-emission intensity at 300 V of this phosphor is close to 180% in comparison with that of commercial red phosphor Y₂O₃:Eu³⁺. An increase of firing temperature to 900°C results in 400-600 nm sized spherical particles. At low voltages (300-800 V), the CL emission of 100 nm sized particles is much stronger than that of 400-600 nm sized ones. In contrast, the larger particles exhibit the higher CL emission intensity at high voltages (1-10 kV). Taking into consideration small spherical morphology and effective CL emission, Li-doped Gd_1.8Y_0.2O₃:Eu³⁺ appears to be an efficient phosphor material for low voltage field emission display.     

Swift heavy ion induced photoluminescence studies in Aluminum oxide

Aluminum oxide, a promising material for high temperature applications, is synthesized by combustion route and characterized by X-ray diffraction technique. Photoluminescence of aluminum oxide bombarded with 120 MeV swift Au⁹⁺ ions have been studied at room temperature. The observed PL emission with peak at ～420 nm is attributed to F-center while the two more weak emissions with peaks at ～482 and ～525 nm are attributed to aggregates of F-centers. It is found that PL intensity increases with increase in Au⁹⁺ ion fluence up to ～1×10¹³ ions cm^?2 and thereafter it reaches saturation. The Fourier transform Infrared spectroscopy results show the destruction of Al?O?H bonds whereas the XRD results indicate the surface amorphization of Al₂O₃.     

Y2O3:Yb3+,Tm3+纳米材料的可见及紫外上转换发光

通过燃烧法制备了Yb³⁺-Tm³⁺共掺的Y₂O₃纳米粉体,并对样品在980 nm激光照射下的上转换发光特性进行了研究.实验发现,样品在可见光区域能够产生强烈的蓝色发光(476 nm和487 nm)和较弱的红色发光(约650 nm),而且同时观察到了两个紫外发光峰¹I₆→³H₆ (~297 nm)和^{1关键词： 2O₃:Yb3+')" href="#">Y₂O₃:Yb3+ 3+}')" href="#">Tm³⁺ 上转换光谱 敏化 紫外发光     

Upconversion white-light emission in Ho³⁺/Yb³⁺/Tm³⁺ tridoped LiNbO₃ single crystal

Ho³⁺/Yb³⁺/Tm³⁺ tridoped LiNbO₃ single crystal exhibiting intense upconversion white light under 980?nm excitation has been successfully fabricated by the Czochralski method. The tridoped LiNbO₃ single crystal offers power dependent color tuning properties by simply changing excitation power. Efficient three-photon blue upconversion emission and two-photon green and red upconversion emissions have been observed. In addition, the red emission of Ho³⁺ originates dominantly from the nonradiative decay of green emission. The LiNbO₃ with upconversion white light will be a potential laser candidate material.     

LUMINESCENCE OF Bi3+ and Eu2+ DOUBLE CENTERS DOPED IN CaS HOST

In this work, double-center.doped luminescent material CaS:Bi³⁺, Eu²⁺ was made via flux NH₄Cl by sintering in excess sulfur environment. The sample had a purplish red net luminescent color. Excitation spectra at both red, 650 nm and blue, 487 nrn were taken. The red emission from Eu²⁺ center was mainly come from the 4f⁶5d¹ absorption in the CaS host. The blue emission from the Bi³⁺ center on the other hand showed no big difference from the singly doped CaS:Bi³⁺ materials in excitation spectrum. Emission spectra were obtained at excitaton of 270nm and 300nm. Stokes shift was moved about 20-30nm, under different point excitation. Emission peaks of both Bi³⁺ and Eu²⁺ centers appeared at 463nm, 642.5nm by 270nm excitation and 487 nm, 620 nm by 300 nm excitation respectively. After-glow decay cures were also obtained and the shapes of decay curves are similar and it is due to the single hole-trap system by lattice defects.