Relative Luminescence Intensity Research Articles

Effect of spectrum-control in dual-wavelength light-emitting diode by doped GaN interval layer

A two-dimensional simulation of electrical and optical characteristics of dual-wavelength LED (light-emitting diode) with doped GaN interval layer is conducted with software.It shows that by the use of doped GaN interval layer, we can solve the luminescence intensity disparity of the two kinds of quantum wells in dual-wavelength LED. And through control of the thickness of the interval layer, we can adjust the relative luminescence intensity of the two kinds of quantum wells. Therefore, the effect of spectrum-control in dual-wavelength LED is due to the blocking effect of holes or electrons by doped GaN interval layer.

Effects of Sr 2+ on structure and luminescent properties of BaAl 12O 19:Eu phosphors

Ba 0.9- y Sr y Al 12O 19:Eu 0.1 phosphors were prepared by sol-gel technique, the crystalline structures of samples characterized by XRD, and the luminescence properties were investigated. The influence of crystallographic positions on the luminescent properties of Sr 2+-doped BaAl 12O 19:Eu was investigated in detail. The results indicated that the crystal lattice of BaAl 12O 19:Eu was not influenced by the Sr 2+ and doping Sr 2+ in BaAl 12O 19:Eu enhanced the luminescent properties of the phosphors at the proper concentration of Sr 2+. With the increasing of concentration of Sr 2+ doped in BaAl 12O 19:Eu, the relative luminescent intensity of Ba 0.9- y Sr y Al 12O 19:Eu 0.1 strengthened and blue-shifted.

Photoluminescence study of SiO 2 coated Eu 3+:Y 2O 3 core-shells under high pressure

Uniform core-shell Eu 3+:Y 2O 3/SiO 2 spheres were synthesized via precipitation and the Stöber method. The structural transition of core-shell Eu 3+:Y 2O 3/SiO 2 was studied by using high pressure photoluminescence spectra. With pressure increasing, the emission intensities of 5D 0→ 7F 0,1,2 transitions of Eu 3+ ions decreased and the transition lines showed a red shift. The relative luminescence intensity ratio of 5D 0→ 7F 2 to 5D 0→ 7F 1 transitions decreased with increasing pressure, indicating lowering asymmetry around Eu 3+ ions. During compression, structural transformation for cores in the present core-shell Eu 3+:Y 2O 3/SiO 2 sample from cubic to monoclinic took place at 7.5 GPa, and then the monoclinic structure turned into hexagonal above 15.2 GPa. After the pressure was released, the hexagonal structure transformed back to monoclinic and the monoclinic structure was kept stable to ambient pressure.

Measured coral luminescence as a freshwater proxy: comparison with visual indices and a potential age artefact

Illuminating slices from massive coral skeletons under ultraviolet light can reveal bright luminescent lines in nearshore corals affected by freshwater river flows. The occurrence and intensity of these lines in long-lived corals can then be used to reconstruct past river flow and rainfall, extending the instrumental records of past tropical climate variability considerably. Earlier studies from the Great Barrier Reef, Australia, have used visual assessments of luminescent line intensity to develop semi-quantitative (though potentially subjective) indices of spatial and temporal variations in freshwater flows. Annual visual assessments and relative coral luminescence intensity (measured by fluorescence spectroscopy) and growth variables are first compared for 89 Porites coral colonies from 30 reefs throughout the length and breadth of the GBR. This demonstrates that simple visual assessments can provide useful information, in the absence of quantitative measurements, of this proxy freshwater tracer. The annual range of measured luminescence between the preceding winter minimum and summer maximum, rather than annual average or annual maximum luminescence is shown to be the most robust measure of freshwater flow. Second, from analyses of the coral colony data and over 40-century-long or longer coral core records, attention is drawn to a potential age artefact in annual average and annual maximum measured coral luminescence. These variables show a significant decline through time, similar to the observed decline in average skeletal density. Although the reasons for this decline are unknown, it could compromise interpretation of long-term variations in freshwater flows and subsequent climatic inferences. This artefact does not appear to affect the annual luminescence range which, it is concluded, is a robust proxy for inter-annual variations in river flow and rainfall.

A modified solution combustion method to superfine Gd 2O 3:Eu 3+ phosphor: preparation, phase transformation and optical properties

Cubic and monoclinic Gd 2O 3:Eu 3+ phosphors in the range of nano-scale and submicron-scale were prepared by a modified solution combustion method. Coexistence of cubic and monoclinic phases was found in the highest luminescent sample synthesized at 600 °C. In relation to commercial sample, the relative luminescence intensity was 49.8%. The shape of emission spectrum of the sample thus changed and the charge-transfer-state band of excitation spectrum slightly shift toward higher energies. With increasing the annealing temperature, phase transformation and correlative optical properties of Gd 2O 3:Eu 3+ phosphors were studied. It was found that the samples were dominated by cubic structure and monoclinic structure at temperatures below and above 900 °C.

(Invited) Novel Processing for Si-Nanocrystal Based Photonic Materials

We report a study of novel processing approaches for the formation of silicon nanocrystals for photonic devices. A silicon rich oxide was formed using ion implantation into thermally grown oxides on Silicon and transparent sapphire substrates. These layers were then treated with rapid thermal processing to observe the formation of silicon nanocrystals on a one second to ten minute timescale. Transmission electron microscopy and Raman scattering were used to follow the evolution of the nanocrystal mean diameter with anneal time. Identical samples co-implanted with Erbium demonstrated the widely reported non-resonant energy transfer mechanism from the nanocrystals to the internal energy levels of the erbium. We quantified the sensitization efficiency, IEr/Inc as a function of the Si-NC size by correcting the relative visible and IR luminescence intensities for variations in the nanocrystal density and observed photoluminescence lifetime. We find that the sensitizing efficiency increases exponentially with decreasing Si-NC mean diameter.

Influence of saliva substitute films on the initial adhesion of Candida albicans to dental substrata prior to and after artificial ageing

Objective The aim of this in vitro study was to investigate whether saliva substitute films influence the adhesion of Candida albicans to different dental substrata prior to and after artificial ageing. Design Specimens of a denture base resin (DB) and a veneering composite (VC) were polished and subjected to an artificial ageing protocol (thermal cycling, 2 × 3000 cycles 5/55 °C). Bovine enamel (BE) and glass were used as reference materials. After determination of surface free energy, specimens were rinsed with commercial saliva substitutes ( Aldiamed, Saliva natura, Saliva Orthana, Salinum), a positive control (protein mixture), or a negative control (Phosphate Buffered Saline, PBS) for 2 h at 37 °C in a flow chamber. Specimens were then exposed to a C. albicans ATCC 10231 suspension for 4 h at 37 °C. Adherent, viable Candida cells were quantified using a luminometric ATP-based assay. Statistical analysis was performed using 1- and 2-way ANOVA, and post-hocs were analysed using the Tukey–Kramer test ( α < .05). Results Our data indicated that VC (31.1 mJ/m 2) and DB (33.9 mJ/m 2) yielded the lowest surface free energy prior to artificial ageing, and BE (43.6 mJ/m 2) yielded the highest surface free energy. For C. albicans adhesion, both the materials as well as the saliva substitutes influenced relative luminescence intensities, indicating significant differences in C. albicans adhesion between the various materials and after treatment with the saliva substitutes. Conclusions Saliva substitutes may have a decisive influence on C. albicans adhesion, but their impact appears to be dependent on the properties of the underlying substratum material.

Development of a device for chemiluminescence determination of superoxide generated inside a dialysis hollow-fiber membrane

Reactive oxygen species (ROS) generated during hemodialysis treatment cause dialysis complications because of the high reactivity of ROS. To prevent dialysis complications caused by oxidative stress, it is important to evaluate the generation and dismutation of ROS during hemodialysis treatment. In this study, our aim was to develop a device to determine superoxide (O(2)(-)) generated inside a dialysis hollow fiber, and also to examine whether this device could detect O(2)(-) separated from plasma using hollow fibers. Experimental apparatus was set up so that hypoxanthine (HX) solution flowed inside the hollow fibers and 2-methyl-6-p-methoxyphenylethynyl-imidazopyrazinone (MPEC) solution flowed outside the hollow fibers. Then, xanthine oxidase (XOD) solution was added to the HX solution to generate O(2)(-), and chemiluminescence resulting from the reaction of O(2)(-) with MPEC was measured with an optical fiber. Chemiluminescence intensity was measured at different HX concentrations, and the peak area of relative luminescence intensity yielded a first-order correlation with the HX concentration. Based on the relationship between HX and O(2)(-) concentrations determined by the cytochrome c reduction method, the relative luminescence intensity measured by this device was linearly dependent on the O(2)(-) concentration inside the hollow fibers. After modifications were made to the device, XOD solution injection into plasma including HX resulted in an increase in the relative luminescence intensity. We concluded that this novel device based on chemiluminescence is capable of determining aqueous O(2)(-) generated inside a hollow fiber and also of detecting O(2)(-) in plasma.

Greenish‐Yellow Emission from Dy3+‐Doped Y2O3 Nanophosphors

Trivalent dysprosium‐doped cubic yttrium oxide (Y2O3) nanophosphors were prepared by combustion synthesis using glycine as fuel. The resulting products were characterized by Raman and FT‐IR spectra to evaluate the vibrational features of the samples. X‐ray diffraction patterns confirmed the formation of a pure cubic phase of Y2O3. The morphology and selective area electron diffraction measurements were carried out using transmission electron microscopy (TEM) and field‐emission scanning electron microscopy. From TEM, it is observed that as‐prepared particles have average crystallite sizes of around 23 nm. The luminescent and dynamic properties of Y2O3:Dy3+ were examined as a function of temperature and different concentrations of Dy3+. The luminescence study reveals that these phosphors predominantly exhibit greenish‐yellow emission due to strong 4F9/2→6H13/2 transition at 575 nm and a feeble 4F9/2→6H15/2 transition at 488 nm. These results show that the relative luminescence intensity of emission bands changes with different heating temperatures, while the greenish yellow color luminescence as well as Commission International d'Eclairage chromaticity coordinates extracted from the emission spectra were not affected significantly. The strong greenish‐yellow emission of Y2O3:Dy3+ phosphor may be useful for applications in solid‐state white lamps for general illumination purposes.

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.

Efficient UV–visible up-conversion emission in Er3+/Yb3+ co-doped La2O3 nano-crystalline phosphor

A nano-crystalline La2O3: Er3+/Yb3+ phosphor sample has been synthesized through the solution combustion route using urea as a reducing agent. Thermal, structural and optical characterizations have been carried out to explore several of its properties. By thermal analysis one concludes to the presence of moisture and hydroxide phases [La(OH)3 and LaOOH] of lanthanum in the as-synthesized sample, which further changes to La2O3 phase above 600°C temperature. Up-conversion (UC) study shows the intense emission bands in the UV, blue, green and red regions. This paper also reports the first observation of UC emission bands extending up to the UV (240 nm) region on excitation with 976 nm wavelength. Heat treatment of the samples shows a change in the crystallite phase along with crystallite growth and relative UC luminescence intensities. The input pump power dependence shows the involvement of up to four photons.

Polyvinylpyrrolidone (PVP)-assisted hydrothermal synthesis of luminescent YVO 4:Eu 3+ microspheres

Spherical YVO 4:Eu 3+ microstructures were hydrothermally synthesized by the reaction of NH 4VO 3, Y 2O 3, and Eu 2O 3 at 180 °C for 24 h with the assistance of polyvinylpyrrolidone (PVP) as a surfactant. The resulting products were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) spectroscopy. The experimental results showed that ball-like YVO 4:Eu 3+ microspheres with a diameter of about 4–5 μm, corresponding to the SEM observations, formed at 180 °C for 24 h using 0.2 g PVP with the molecular weight of 20,000 g mol −1. The amount of PVP and the reaction time of hydrothermal processing were found to play a key role in the formation of YVO 4:Eu 3+ microspheres. It has been observed that the relative luminescence intensities of the as-synthesized samples increased with increasing hydrothermal reaction times due mainly to the increase of crystallinity.

The special features of the luminescence and light resistance of europium complexes and their mixtures with lanthanum complexes in polymethyl methacrylate

The kinetics of luminescence and transformation of short-lived products of the photolysis of europium and lanthanum complexes with thenoyltrifluoroacetone and 1,10-phenanthroline and their mixtures in polymethyl methacrylate films was studied by the nanosecond laser photolysis method with recording both light emission and absorption. Fast (535 and 585 nm, 5 D 1 → 7 F 0, 7 F 3, decay time 0.7 μs) and slow (613 nm, 5 D 0 → 7 F 2, luminescence rise and decay times 0.7 μs and 0.5 ms, respectively) luminescence was studied. Induced absorption with a maximum at 600 nm and decay time ∼3 ms was observed; this absorption was assigned to triplet states of the deprotonated form of thenoyltrifluoroacetone. The dependences of luminescence intensity on the concentration of the components in a mixture of complexes were analyzed, and synergistic effects of luminescence strengthening were estimated. The kinetics of a decrease in luminescence intensity during photolysis was studied. Possible mechanisms of a decrease in the relative initial process rate and an increase in the quasi-stationary value of relative luminescence intensity as the concentration of complexes in the polymer increased were discussed.

White upconversion of rare-earth doped ZnO nanocrystals and its dependence on size of crystal particles and content of Yb3+ and Tm3+

Rare earth (RE) doped ZnO nanocrystals were synthesized by chemical combustion method. Bright white upconversion (UC) luminescence with the CIE coordinates close to (0.33, 0.33) was obtained in Er+Tm+Yb tridoped ZnO nanocrystals under the excitation of a cost-effective 980 nm single-wavelength laser diode. The overall and relative UC luminescence intensities of RE doped ZnO nanocrystals were found to be depended highly on the diameter of crystal particles and the concentration of Yb3+ and Tm3+, for which the involved mechanisms were demonstrated. The investigation based on UC spectra, simplified energy level diagram, and excitation power dependence indicated that the remarkable enhancement of the green emission of the RE tridoped sample was due to a dual sensitization of Er3+ by Yb3+ and Tm3+ ions. The RE tridoped ZnO nanocrystals with the CIE coordinates close to (0.33, 0.33) are potentially suitable for the widely realistic application as the multicolor fluorescent labels, due to a fact that they could be cheaply and easily obtained and excited cost effectively.

Preparation, characterization, and optical properties of nano- and submicron-sized Y2O3:Eu3+ phosphors

Ultrafine Y2O3:Eu3+ phosphors were prepared by a modified solution combustion method. The as-prepared samples with sizes of 17.6–80 nm (nanophosphors) and 300 nm (submicron phosphors) were characterized by x-ray diffraction, transmission electron microscope, scanning electron microscopy, selected area electron diffraction, and energy dispersive x-ray spectroscopy. The emission spectra of the samples are unchanged in comparison with that of standard material. The excitation spectra show a redshift in the charge-transfer-state band and a blueshift in the host gap band. In relation to commercial sample, the relative luminescence intensities of nano- and submicron phosphors are increased sufficiently to 64.4% and 93.6%, respectively. Higher quenching concentration of the activator Eu3+ ion was observed in the nanophosphor than that in the phosphor synthesized by solid state reaction.

Multifunctional Er3+–Yb3+ codoped Gd2O3 nanocrystalline phosphor synthesized through optimized combustion route

This paper reports the synthesis of high upconversion luminescent Gd2O3: Er3+, Yb3+ nanophosphor through optimized combustion route using urea as a reducing agent. The paper also reports the first observation of upconversion emission bands extending upto the UV region (335, 366 and 380 nm) in Er3+–Yb3+ co-doped phosphor materials. The fuel to oxidizer ratio has been varied to obtain the maximum upconversion luminescence. Three high intensity bands are found at 408, 523–548 and 667 nm due to the 4G11/2 → 4I15/2, 2H11/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions, respectively, along with the other bands. Input excitation power dependence has been studied for different transitions, and the saturation effect and decrease in the slope of different transitions at higher input pump power has been explained. Heat treatments of the samples show change in crystallite phase/size and relative upconversion luminescence intensities of blue, green and red bands. The color of the phosphor emission has shown to be tunable with change in the crystal structure as well as on excitation laser power and Er3+–Yb3+ concentration. The property of color tunability of the phosphor material has been used to record the fingerprint in different colors. Also, the future prospect of the nanocrystalline phosphor material as a sensor for temperature, using FIR method, has been explored.

Structural and optical studies of Eu3+ ions in alkali borate glasses

Europium-doped borate-based glasses (Eu3+:MBE (M = Na, K and Na + K)) have been prepared by a melt quenching technique and characterized optically. FTIR spectra and XRD patterns were used to analyze the glass structure. The spectroscopic properties such as optical absorption and photoluminescence spectra and decay time measurements for the 5D0 level of Eu3+ ions were obtained. A strong red fluorescence is observed from the 5D0 level of Eu3+ ions in these glasses. Judd–Ofelt (JO) parameters have been evaluated from the luminescence intensity ratios of 5D0 → 7FJ (J = 2 and 4) to 5D0 → 7F1 transitions. These parameters have been used to derive radiative properties such as transition probabilities, branching ratios, radiative lifetimes and peak stimulated emission cross sections for the 5D0 → 7FJ transitions. The relative luminescence intensity ratio (R) of 5D0 → 7F2 to 5D0 → 7F1 transitions has been evaluated to estimate the local site symmetry around the Eu3+ ions. Relatively higher values of R and the JO parameter Ω2 for the Eu3+:MBE glasses suggest a lower symmetry for Eu3+ ions and a higher Eu–O covalence. Decay curves of the 5D0 level of Eu3+ ions have been measured by monitoring the 5D0 → 7FJ transition (at around 612 nm) at room temperature. The experimental lifetime of the 5D0 level in these glasses is found to be lower than Eu3+-doped phosphate glasses and comparable to or higher than Eu3+-doped niobium phosphate or tellurite glasses. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Spectral analysis of Eu 3+:B 2O 3–Al 2O 3– MF 2 ( M = Zn, Ca, Pb) glasses

The influence of glass composition on the optical properties of Eu 3+-doped borate glasses modified with Zn 2+, Ca 2+ and Pb 2+ cations has been investigated. These glasses have been prepared by melt quenching technique and characterized through optical absorption, photoluminescence and decay times. An intense red luminescence is observed from the 5D 0 emitting level of Eu 3+ ions in these glasses. The relative luminescence intensity ratio of 5D 0 → 7F 2 to 5D 0 → 7F 1 transitions has been evaluated to estimate the local site symmetry around the Eu 3+ ions. Judd–Ofelt parameters have been evaluated from the absorption spectra. These parameters have been used to derive radiative properties such as transition probabilities, branching ratios, radiative lifetimes and peak stimulated emission cross-sections for the 5D 0 → 7F J ( J = 0, 1, 2, 3 and 4) transitions. Decay curves of the 5D 0 level of Eu 3+ ions in these three glass systems have been measured by monitoring the 5D 0 → 7F 2 transition at room temperature.

Rare earth doping of III‐nitride alloys by ion implantation

AbstractThe implantation damage and rare earth (RE) luminescence in the wide band gap ternaries AlGaN and AlInN were studied and compared to GaN. For both ternaries lower damage levels were observed and in contrast to GaN, no surface amorphisation occurs during the implantation. Damage recovery of RE implanted GaN was studied for post implant annealing at temperatures between 800 °C and 1300 °C. The blue and IR Tm related luminescence intensity is seen to increase strongly with the annealing temperature. The two Tm lines observed at 478 nm and 465 nm are assigned to the 1G4 → 3H6 and the 1D2→3F4 transition, respectively. For GaN the line at 465 nm is fully quenched at RT while it becomes the dominant line for the ternaries. The blue luminescence intensity in the ternaries is significantly stronger than in GaN. Furthermore, AlInN shows a very high ratio of blue/IR luminescence. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Blue-light emission of mesoporous SBA-15 covalently bonded with carbazole chromophore

Much attention has been paid to carbazole derivatives for their potential applications as optical materials. For the first time, the blue-light-emitting carbazole chromophore has been covalently bonded to the ordered mesoporous SBA-15 (The resultant hybrid mesoporous materials are denoted as carbazole–SBA-15) by co-condensation of tetraethoxysilane (TEOS) and prepared compound 3-[ N-3-(triethoxysilyl)propyl]ureyl-9-ethyl-carbazole (denoted as carbazole–Si) in the presence of Pluronic P123 surfactant. The results of 1H NMR and Fourier transform infrared (FTIR) reveal that carbazole–Si has been successfully synthesized. Small-angle X-ray diffraction patterns (XRD) and Nitrogen (N 2) adsorption/desorption measurements were employed to characterize the mesostructure of carbazole–SBA-15. Solid-state 29Si magic-angle spinning (MAS) NMR was used to confirm the preservation of the carbazole group and estimate the degree of hydrolysis-condensation. Photoluminescence (PL) measurements show that carbazole–SBA-15(0.07) [carbazole–Si:(TEOS+carbazole–Si) molar ratio is 0.07] hybrid mesoporous material exhibits a monomeric emission in the “light blue” region with a PL quantum yield ∼31%. Compared with carbazole–Si, the I car/ C car (relative luminescence intensity divided by the content of carbazole) of carbazole–SBA-15(0.07) increases 24 times. The luminescence decays for 3-amino-9-ethyl-carbazole (denoted as carbazole–NH 2) and carbazole–Si are single-exponential functions of time, while those for carbazole–SBA-15 mesoporous materials are fitted by double-exponential functions. The stability studies on carbazole–Si and carbazole–SBA-15(0.07) show that the carbazole chromophore in the resultant hybrid mesoporous material exhibits better thermal stability than in carbazole–Si compound. The excellent luminescent properties and thermal stability enable the hybrid mesoporous material to have potential use as blue-light-emitting material in optical field.