Red Line Emission Research Articles

Unique light-induced degradation in yellow-emitting K2SiF6:Mn2+ phosphor

Photo-induced luminescence intensity degradation in yellow-emitting K2SiF6:Mn2+ phosphor is studied using x-ray diffraction measurement, photoluminescence (PL) analysis, PL excitation (PLE) spectroscopy, PL decay analysis, and electron spin resonance (ESR) measurement. The yellow-emitting K2SiF6:Mn2+ phosphor exhibits remarkable degradation in the PL intensity under Xe lamp exposure. Coherent laser irradiation also induces degradation and its degree is in the order of He–Cd (λ = 325 nm) > Ar+ (488 nm) > He–Ne laser (632.8 nm). The degradation mechanism is proposed to be due to change in the valence state of manganese ions from Mn2+ to Mn3+ by the photooxidation (Mn2+ → Mn3+) or disproportionation reaction (2Mn2+ → Mn+ + Mn3+). The ESR measurement confirms the decreased Mn2+ spin density in the sample exposed with Xe lamp. The PLE spectrum suggests that the excitation of Mn3+ ions occurs through energy transfer upon absorption of exciting radiation by the Mn2+ ions. Thermal annealing of the degraded samples at ≥200 °C causes a blueshift in the PL emission band with an appearance of the Mn4+-related sharp red emission lines.

Synthesis and luminescence properties of Li2O–Y2O3–TeO2:Eu3+ tellurite glass

The Eu3+-doped red-orange emitting phosphor of tellurite glass 0.25Li2O–0.20Y2O3–0.5TeO2–0.05Eu2O3 has been synthesized by the melt quenching method. The amorphous nature of the glass has been verified by XRD measurements. The photoluminescence excitation and emission spectra, the luminescence decay curves have been investigated for the composition. The phosphor can be efficiently excited by the near UV light to realize the intense narrow red emission line (611 nm) corresponding to forced electric dipole transition 5D0 → 7F2 of Eu3+ ions. The Li2O–Y2O3–TeO2:Eu3+glass phosphor is a potential red-orange emitting candidate for the application in WLEDs.

EPR and luminescence studies of Cr3+ doped MgSrAl10O17 phosphor synthesized by a low-temperature solution combustion route

MgSrAl10O17:Cr3+ powder phosphor has been synthesized by a solution combustion method at furnace temperature of 500°C in a short time (< 5min). The as-prepared phosphor was characterized by X-ray diffraction, Fourier transform infrared and scanning electron microscopic techniques. EPR spectrum of Cr3+ ions in MgSrAl10O17 phosphor suggested a variety of symmetries associated with Cr3+ ions. The optical studies show two broad and intense bands characteristic of Cr3+ ions in an octahedral symmetry. Upon 552nm excitation, an intense narrow red emission line centered at 690nm has been observed related to 2Eg→4A2g transition of Cr3+ ions. The crystal field parameter (Dq) and Racah parameters (B and C) have been evaluated and discussed.

Photoluminescence Properties of Eu3+ in Ga2O3−Tb3Ga5O12:Cr3+ Phosphor Synthesized by Metal Organic Deposition

We demonstrated the synthesis of Eu3+-activated Tb3Ga5O12 garnet phosphor by metal-organic deposition and reported the photoluminescence (PL) properties of this garnet phosphor in detail. The phosphors were synthesized from a mixture of organic gallium solution and acetic acid dissolved with TbCl3/Eu2O3. The X-ray diffraction analysis indicated that the synthesized phosphors were a mixture of β-phase Ga2O3 and cubic Tb3Ga5O12 garnet (TGG). The TGG fraction increased with the increase of the TbCl3 addition in the raw solution. The Eu3+ ions were preferentially incorporated into the TGG crystallites rather than β-Ga2O3. The intensities of the Eu3+ emissions in TGG were strongly influenced by the Cr3+ red-line emissions, where the Cr3+ ions were unintentionally introduced in the synthesized phosphors. The PL excitation spectra indicated that the Eu3+ emission at 708 nm (5D0 → 7F4) was gained by the Tb3+ intra-f-shell, Cr3+ intra-d-shell, and charge transfer transitions. Temperature dependences of the Eu3+ and Cr3+ emission intensities were measured at T = 20 − 380 K and explained by the proposed theoretical models very well. The effects of the Eu3+ ion site in the various host materials on the luminous properties were also discussed in detail.

Synthesis and luminescence properties of red long-lasting phosphor Y2O2S:Eu3+, Zn2+, Ti4+ nanotubes via hydrothermal method

Red long-lasting phosphor Y2O2S:Eu3+, Zn2+, Ti4+ nanotubes were prepared by hydrothermal method. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence and thermoluminescence spectra (TL) were used to characterize the long-lasting phosphor. XRD investigation revealed that the product synthesised under 750 °C for 6 h was a pure phase of Y2O2S. SEM observation showed that the sulfuretted phosphor inherited the tube-like shape from the precursor. Under 325 nm UV excitation, the result indicated the strongest red-emission lines at 627 nm, corresponded to the transition from 5D0 to 7F2 level of Eu3+ ion. Both the afterglow decay curves and TL curves revealed that the phosphor had efficient luminescent and excellent long-lasting properties.

Generation of white-light from Dy3+ doped Sr2SiO4 phosphor

A single host lattice white light emitting Sr2SiO4:Dy3+ powder phosphor was synthesized by solid state reaction process using a temperature of 1000°C. The structure, particle morphology, chemical composition and oxidation states, photoluminescence (PL) and decay properties of the phosphor were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy and PL spectroscopy, respectively. The objective of this study was to prepare a phosphor that can be used in white light emitting diodes. The XRD patterns showed a monoclinic structure of Sr2SiO4 with minor incidental secondary phases from unreacted precursors. An agglomeration of particles with irregular shapes was observed from the SEM micrographs. The PL emission spectra of the Sr2SiO4:Dy3+ phosphor excited at 350nm consist of blue, yellow and red line emissions at 486nm, 575nm and 668nm corresponding respectively to the (4F9/2→6H15/2), (4F9/2→6H13/2) and (4F9/2→6H11/2) transitions of Dy3+. The combination of these emissions constituted white light as indicated on the Commission Internationale de L'Eclairage chromatic coordinate diagram. The decay characteristics show that the phosphor consists of a single exponential decay process.

Tunable and white photoluminescence from Tb3+–Eu3+ activated Ca0.3Sr0.7Al2O4 phosphors and analysis of chemical states by X-ray photoelectron spectroscopy

Tb3+ and Eu3+ activated Ca0.3Sr0.7Al2O4 phosphors with tunable emissions were synthesized via urea assisted combustion method. The phosphors were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy and photoluminescence (PL) spectroscopy. The XRD pattern of the Ca0.3Sr0.7Al2O4:Tb3+, Eu3+ powder showed was composed of a single phase associated with monoclinic SrAl2O4, suggesting that SrAl2O4 was the main structure in the Ca0.3Sr0.7Al2O4 mixed aluminate host and Ca2+ substituted the Sr2+ ions. Consistent with the three dimensional structure of SrAl2O4, the XPS data indicated that there were two different lattice sites occupied by Sr2+ in the lattice and resultantly Ca2+ could also be found at two different lattice sites. Tunable and white PL was generated when the phosphors were optically excited at different wavelengths using a monochromatized xenon lamp. The white PL with the Commission International de L’Eclairage (CIE) coordinates (x=0.343, y=0.325) was a result of the combination of the red line emission from Eu3+ and the blue and green line emissions from Tb3+.

Synthesis and luminescence characteristics of Li2Y4–xEux(WO4)7–y(MoO4)y red-emitting phosphor for white LED

Li2Y4–xEux(WO4)7–y(MoO4)y red-emitting phosphors were synthesized by solid state reaction and characterized by powder X-ray diffraction (XRD) and photoluminescence (PL) spectrum. The excitation spectra showed that the phosphors could be efficiently excited by near-UV light of 395 nm. When the relative molar ratio of Mo/W was 7:0, and the optimum doped concentration of Eu3+ was 2.8 mol, the phosphor showed strong red emission lines at 615 nm corresponding to the forced electric dipole 5D0→7F2 transition of Eu3+. Compared with Na2Y2Eu2(MoO4)7 and K2Y2Eu2(MoO4)7, the fluorescence intensity of Li2Y1.2Eu2.8(MoO4)7 phosphor was the strongest. The CIE chromaticity coordinates of Li2Y1.2Eu2.8(MoO4)7 phosphor was calculated to be (0.66, 0.34).

Soft chemical synthesis and luminescence properties of red long-lasting phosphors Y2O2S:Sm3+

Sm3+-activated Y2O2S red phosphors were prepared by the combustion method and microemulsion method at the first time. X-ray characterization and electron diffraction show that, Y2O2S:Sm3+, Ti4+, Mg2+ samples prepared by these two methods are pure hexagonal crystals in structure with a trivial change due to dopants. Scanning electron microscopy (SEM) results show that the product presents an almond-like sheet in uniform size. Under the excitation of 269 nm ultraviolet light, Y2O2S:Sm3+ samples fabricated by these two methods exhibit three main groups of red emission lines located at 564, 604, and 656 nm, respectively, which are attributed to the transitions of 4G5/2 →6H5/2, 4G5/2 →6H7/2, 4G5/2 →6H9/2, respectively. The samples prepared by microemulsion are seven times higher in fluorescent emission intensity and half time longer in afterglow time than that prepared by combustion.

The Keplerian orbit of G2

AbstractWe give an update of the observations and analysis of G2 – the gaseous red emission-line object that is on a very eccentric orbit around the Galaxy's central black hole and predicted to come within 2400 RS in early 2014. During 2013, the laser guide star adaptive optics systems on the W. M. Keck I and II telescopes were used to obtain three epochs of spectroscopy and imaging at the highest spatial resolution currently possible in the near-IR. The updated orbital solution derived from radial velocities in addition to Br-γ line astrometry is consistent with our earlier estimates. Strikingly, even ∼ 6 months before pericenter passage there is no perceptible deviation from a Keplerian orbit. We furthermore show that a proposed “tail” of G2 is likely not associated with it but is rather an independent gas structure. We also show that G2 does not seem to be unique, since several red emission-line objects can be found in the central arcsecond. Taken together, it seems more likely that G2 is ultimately stellar in nature, although there is clearly gas associated with it.

Luminescent properties of red long-lasting phosphor Y2O2S:Eu3+, M2+ (M=Mg, Ca, Sr, Ba), Ti4+ nanotubes via hydrothermal method

Red long-lasting phosphor Y2O2S:Eu3+, M2+ (M = Mg, Ca, Sr, Ba), Ti4+ nanotubes were synthesized by hydrothermal method. The Y2O2S:Eu3+, M2+ (M = Mg, Ca, Sr, Ba), Ti4+ phosphors were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL), and thermoluminescence spectra (TL). The samples doped with different divalent alkaline-earth metal ions were calcined at 750 °C for 6 h in CS2 atmosphere, they were composed of pure Y2O2S phase. SEM observation showed that the sulfuretted phosphors inherited the tube-like shape from the precursors. Under 325 nm UV excitation, the result indicated that the strongest red-emission lines at 627 nm, which corresponded to the transition from 5D0 to 7F2 level of Eu3+ ion. The afterglow property of phosphors doped with different divalent alkaline-earth metal ions decreased according to the order of Mg2+, Sr2+, Ca2+, Ba2+. For the sample doped with Mg2+, the trap depth was 1.32 eV and the decay time could last for over 1065 s (⩾1 mcd/m2) after 365 nm UV radiation for 10 min.

KECK OBSERVATIONS OF THE GALACTIC CENTER SOURCE G2: GAS CLOUD OR STAR?

We present new observations and analysis of G2 - the intriguing red emission-line object which is quickly approaching the Galaxy's central black hole. The observations were obtained with the laser guide star adaptive optics systems on the W. M. Keck I and II telescopes and include spectroscopy (R ~ 3600) centered on the Hydrogen Br-gamma line as well as K' (2.1 micrometer) and L' (3.8 micrometer) imaging. Analysis of these observations shows the Br-gamma line emission has a positional offset from the L' continuum. This offset is likely due to background source confusion at L'. We therefore present the first orbital solution derived from Br-gamma line astrometry, which when coupled with radial velocity measurements, results in a later time of closest approach (2014.21 +/- 0.14), closer periastron (130 AU, 1900Rs), and higher eccentricity (0.9814 +/- 0.0060) compared to a solution using L' astrometry. The new orbit casts doubt on previous associations of G2 and a low surface brightness "tail". It is shown that G2 has no K' counterpart down to K' ~ 20 mag. G2's L' continuum and the Br-gamma line-emission is unresolved in almost all epochs; however it is marginally extended in our highest quality Br-gamma data set from 2006 and exhibits a clear velocity gradient at that time. While the observations altogether suggest that G2 has a gaseous component which is tidally interacting with the central black hole, there is likely a central star providing the self-gravity necessary to sustain the compact nature of this object.

Crystal structure and luminescence properties of Eu2+ activated Sr12Al14O32Cl2: A potential green-emitting phosphor for near UV light-emitting diodes

Abstract A novel green-emitting Sr12Al14O32Cl2:Eu2+ phosphor was synthesized and its crystal structure, photoluminescence properties was investigated. Sr12Al14O32Cl2 crystallizes as a cubic structure with a space group of I 4 ¯ 3 d and lattice constants of a = 12.3471(7) A, V = 1882.35(8) A3. Sr12Al14O32Cl2:Eu2+ can be efficiently excited in the wavelength range of 260–450 nm. When excited at 355 nm, it emit a broad band in the wavelength range of 450–600 nm with a maximum intensity at about 523 nm due to the 4f65d1-4f7 transitions of Eu2+. Weak red line emissions of Eu3+ were also observed in the emission spectra, indicating the coexistence of Eu2+ and Eu3+ ions in the sample. The Sr12Al14O32Cl2:Eu2+ would be a potential candidate green phosphor for near UV light-emitting diodes.

SiO2@YBO3:Eu3+ Hollow Mesoporous Spheres for Drug Delivery Vehicle

A novel bifunctional (fluorescent, mesoporous) hollow sphere was prepared by coating luminescent YBO3:Eu(3+) nanoparticles onto uniform hollow mesoporous silica spheres (HMSs), derived from an etching strategy using spherical Fe3O4 as templates. The composites exhibit typical mesoporous shells, large interior space, high surface area, and well dispersed nanospheres with controlled size. In addition, the textural properties including the specific surface and pore volume can be easily altered by simply tuning of the spherical Fe3O4 cores. Upon ultraviolet (UV) excitation, the composite shows the characteristic (5)D0-(7)F1-4 red emission lines of Eu(3+) even after loading of the model drug. The composite with a large surface area and cavity was used as the host for loading the anticancer drug doxorubicin hydrochloride (DOX). It is observed that the multifunctional composites exhibit an obvious sustained release property and released in texture- and pH-sensitive patterns. Particularly, the down-conversion (DC) fluorescence intensity of the bifunctional vehicle increases with the release of drug molecules, making it possible to track the position and the drug release amount of the drug carrier system and to detect them by the change of fluorescence intensity.

Photoluminescence properties of the red phosphor YInGe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;7&lt;/sub&gt;:Eu&lt;sup&gt;3+&lt;/sup&gt;

Eu 3+ -doped YInGe 2 O 7 phosphors were prepared via a solid-state reaction with metal oxides and their excitation and emission spectra were measured at room temperature. The results showed that pure-phase YInGe 2 O 7 could be obtained after firing at 1250 °C. The maximum photoluminescence intensity of YInGe 2 O 7 :Eu 3+ phosphor was achieved when doped with 40 mol% Eu 3+ ions. Compared with Y 2 O 2 S:0.05Eu 3+ , the Y 0.60 InGe 2 O 7 :Eu 3+ 0.40 phosphor obtained showed intense red-emission lines at 616 nm, corresponding to forced electric dipole 5 D 0 → 7 F 2 transitions of Eu 3+ under 394 nm light excitation. The International Commission on Illumination chromaticity coordinates of the phosphors ( x = 0.644, y = 0.356) of Y 0.60 InGe 2 O 7 :Eu 3+ 0.40 were close to National Television Standard Committee standard values. As such, the synthesized phosphors may find applications in near ultraviolet InGaN chip-based white light-emitting diodes. KEY WORDS : Optical materials, X-Ray diffraction, Luminescence, Solid state reaction Bull. Chem. Soc. Ethiop. 2013 , 27(2), 315-319. DOI: http://dx.doi.org/10.4314/bcse.v27i2.18

Relationship of the nightglow 630.0 nm emission intensity to the solar extreme ultraviolet

It is well known that the 630.0nm nightglow emission intensity at mid latitudes increased more than twofold in periods of maximum sunspot activity. It is assumed that this phenomenon is caused by variations in solar ultraviolet radiation intensity in solar activity cycles (Fishkova, 1983).In this paper, we present the results of photometric measurements of the nightglow emission intensity at 63°N and 130°E (Yakutsk) in 1990–2007. Moreover, we show the dependence of the 630.0nm emission intensity in magnetically quiet days on solar activity in the 22nd and 23rd cycles. It was established that there is a close relationship between the 630.0nm line nightglow intensity and the solar extreme ultraviolet (EUV) intensity based on SOHO/SEM data, obtained in 1997–2007 with a correlation coefficient of 0.8–0.9. The changes of ionization level of nighttime F2 layer at the Yakutsk station and neutral composition of the upper atmosphere (thermosphere) during the photometric observations have been analyzed. It is shown that the long-term variations of the red line emission intensity are caused by the change of nighttime F2 layer electron density. The nighttime ionization level is related to the electron density of the daytime F2 region which depends on the EUV flux intensity during a solar activity cycle.

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.

Structural and luminescence properties of Sr2VO4Cl and Sr5(VO4)3Cl: self-activated luminescence and unusual Eu3+ emission

Novel self-activated vanadate phosphors, blue-emitting Sr2VO4Cl and green-emitting Sr5(VO4)3Cl, were synthesized via the solid-state reaction route, and the relationship between the structure and luminescence properties was comparatively investigated. Self-activated luminescence originating from the VO43− charge transfer (VCT) transition in relation to different V–O distances was verified in two vanadate phases with different crystal structures. Sr2VO4Cl showed a blue emission band from 375 to 600 nm with a peak at 424 nm, while Sr5(VO4)3Cl exhibited a green emission band from 375 to 700 nm with a peak at 517 nm. With the introduction of Eu3+ to Sr2VO4Cl, both the VCT and Eu3+ emissions were found; however, the VCT emission was quenched in Sr5(VO4)3Cl after Eu3+ doping. Sr5(VO4)3Cl:Eu3+ only shows the characteristic red emission lines originating from Eu3+, while Sr5(VO4)3Cl:Eu3+,Na+ shows typical emissions coming from the VCT transition and the Eu3+ ions. As a comparison, the emission intensity of Sr2VO4Cl:Eu3+,Na+ decreased compared to that of Sr2VO4Cl:Eu3+. The intrinsic luminescence mechanism is discussed based on the differences in the crystal structures and the measured lifetimes.

Luminescence and structure of a novel red-emitting phosphor Eu3+-doped tellurate garnet Li3Y3Te2O12

Eu3+-doped red-emitting phosphors of tellurate garnets Li3Y3−3xEu3xTe2O12 (x=0.05–1) were synthesized by the solid-state reaction. The phase purity of the as-prepared phosphor was verified by X-ray diffraction (XRD) studies. The photoluminescence excitation and emission spectra, the fluorescence decay curves, the dependence of luminescence intensity on doping level and CIE coordinates were investigated. The phosphor can be efficiently excited by near UV and blue light to realize an intense narrow red emission line (611nm) corresponding to the forced electric dipole transition 5D0→7F2 of Eu3+ ions. The potential application as a red-emitting phosphor for solid state lighting was evaluated in comparison with Eu3+-doped Y2O2S and aluminum garnet phosphors. The phosphor can be suggested to be a potential red-emitting candidate for the application in white LEDs under the irradiation of near-UV or blue chips.

Variation of Emission Line Width in Mid- and High-Latitude Corona

Spectroscopic studies of the solar corona, using the high spatial and spectral resolution 25-cm coronagraph at the Norikura observatory for equatorial off-limb observations, indicated that the variation of radiance and line width with height is different for different temperature lines. The line width of the forbidden red emission line [\FeX] 6374 \AA was found to increase with height and that of the green emission line [\FeXIV] 5303 \AA decrease with height. This had been interpreted in terms of the interaction between different temperature plasma but needed to be confirmed. Further observations were made on several days during 2004, in two emission lines simultaneously covering the mid-latitude and polar regions to investigate the existence of the observed variation in other parts of the solar corona. In this study, we have analysed several raster scans that cover mid- and high-latitude regions of the off-limb corona in all four bright emission lines [\FeX] 6374 \AA, [\FeXI] 7892 \AA, [\FeXIII] 10747 \AA, and [\FeXIV] 5303 \AA. We find that the FWHM of the red line increases with height and that of the green line decreases with height similar to that observed in equatorial regions. The line widths are found to be higher in polar regions for all of the observed emission lines except for the green line. Higher values of FWHM in polar regions may imply higher non-thermal velocities which could be further linked to a non-thermal source powering the solar-wind acceleration, but the reason for the behaviour of the green emission line remains to be explored.