Variation Of Emission Spectra Research Articles

In-situ synthesis of SiC/SiO2 nanowires by catalyst-free thermal evaporation of silicon powder and their photoluminescence properties

Core-shell structured SiC/SiO2 nanowires (SiC/SiO2 NWs) were synthesized by a simple thermal evaporation method without a catalyst. The influence of the growth temperature and holding time on the microstructure and composition of the nanowires were investigated. The results indicate that within the temperature range of 1150 to 1550 °C, the color of SiC/SiO2 nanowires gradually transitions from pure white to off-white with increasing temperature. During this process, the average diameter of SiC/SiO2 increases from ∼74 nm to ∼291 nm, while the surface SiO2 layer thickness decreases from ∼17 nm to ∼5 nm, with nanowires can reach lengths of hundreds of micrometres. Variations in supersaturation of SiO and CO at different temperatures lead to discrepancies in nanowire diameter and SiO2 shell thickness. At 1350 °C, prolonged holding time enhances silicon powder reaction, resulting in increased structural disorder of the obtained SiC/SiO2 nanowires. The nanowire growth follows a vapor-solid (VS) mechanism. Additionally, the study demonstrates that the photoluminescence (PL) characteristics of the nanowires exhibit a blue shift attributable to their nanoscale dimensions, while variations in emission spectra correlate with stacking faults, SiC diameter, and SiO2 thickness. This work may be provide a theoretical basis for preparing SiC/SiO2 nanowires with different diameters and SiO2 shell thicknesses, which is crucial for advancing the development and application of SiC/SiO2 nanoceramics.

Original KGd2F7 nanocrystals in fluoro-oxide glass ceramics by Dy3+/Sm3+ co-doped for white light emission

Serial fluoro-oxide glass ceramics (GCs) containing 0.6 mol% Dy 3+ and various Sm 3+ from 0 mol% to 1.5 mol% co-doped novel KGd 2 F 7 nanocrystals were firstly fabricated through high temperature melt-quenching method. Then the microscopic structure of the GCs was revealed by transmission electron microscopy (TEM). And the rare-earth ions (RE 3+ ) of Dy 3+ and Sm 3+ were successfully doped in monoclinic-phase KGd 2 F 7 nanocrystals, which can be verified by energy-dispersive X-ray spectroscopy (EDX) mappings. The photoluminescence spectra of the GCs were probed systematically utilizing 365 nm excitation light. The yellow (573 nm), green (486 nm), and red (648 nm) multiple emissions were observed in the co-doped GCs, and the intensity of red became stronger because of the higher Sm 3+ doping concentrations. This contribution of multiple emissions is due to the co-absorption of both Dy 3+ and Sm 3+ for 365 nm and the presence of energy transfer (ET). Moreover, the ET between Dy 3+ and Sm 3+ was confirmed from the variations of emission spectra and measured decay curves of emissions. Furthermore, the maximum energy transfer efficiency (ETE) from Dy 3+ to Sm 3+ can reach ~60.34% and the internal quantum yield (QY) is computed to be around 31.82% upon excitation of 365 nm. The chromaticity coordinates (CIE (Commission Internationale de L′Eclairage)− 1931) of the GCs can be tuned effectively through changing activator concentrations. Ideal white light emission is at the CIE (0.3357, 0.3342), which was achieved for 0.6 mol% Dy 3+ /0.9 mol% Sm 3+ doped GCs sample. The results indicated that Dy 3+ /Sm 3+ co-doped GCs with both high thermal and chemical-physical stabilities have strong potential application in white light-emitting diodes and fluorescent display devices. • The Dy 3+ /Sm 3+ co-doped fluoro-oxide glass ceramics containing novel KGd 2 F 7 nanocrystals were firstly fabricated. • The Dy 3+ and Sm 3+ ions were successfully doped in monoclinic-phase KGd 2 F 7 nanocrystals. • The standard white light emission was obtained by changing the concentration of Sm 3+ . • The energy transfer process from the Dy 3+ to Sm 3+ has been verified to dipole-dipole interaction mechanism. • The fluoro-oxide glass ceramics containing KGd 2 F 7 nanocrystals exhibit high thermal stability.

Structural modifications and extended optical properties of Ni1-xCoxWO4 nanoparticles

We studied the effect of cobalt doping on structural and optical properties of NiWO4 nanoparticles. Different compositions of cobalt-doped NiWO4 were synthesized using direct chemical precipitation method. X-ray diffraction patterns of Ni1-xCoxWO4 nanoparticles revealed variation in average crystallite size and micro-strain without any change in the standard crystal structure. Transmission electron microscopy studies showed a deviation of particles size and morphology of the samples with a change in dopant concentration. Raman and Fourier transformed infrared spectroscopy also confirmed the standard NiWO4 profiles at different doping ratios. UV-VIS-NIR spectroscopy gave the information related to the bandgap tuning with the change in dopant concentration. It is also confirmed dual direct-indirect nature of bandgap in Ni1-xCoxWO4 nanoparticles. Photoluminescence emission spectroscopic studies displayed variation in emission spectra and colour with cobalt doping.

Emission dynamics of GaN-based blue resonant-cavity light-emitting diodes

We fabricated GaN-based blue resonant-cavity light-emitting diodes (RCLEDs) by inserting InGaN quantum well (QW) active region between two dielectric distributed Bragg reflectors (DBRs). Due to the different gain enhancement factors in a single device, multi-longitudinal modes were observed and tuned with changing the injection current density: pure-blue (PB) at low current density, violet-blue (VB) at intermediate current density, and PB again at high current density. The variation of emission spectra is explained by the competition between band-filling effect and self-heating effect.

Self-contained InGaN/GaN micro-crystal arrays as individually addressable multi-color emitting pixels on a deformable substrate

InGaN/GaN micro-crystals (μ-crystals) are self-contained and individually-addressable light emitting crystals that have unique potential in the development of ultra-small and ultra-high resolution pixels for next-generation displays. In this study, we explore the electrically-driven light emission behavior of vertically standing InGaN/GaN micro-crystals (μ-crystals) with well-defined crystal facets and tunable size. InGaN/GaN μ-crystals have hollow pedestals weakly bound to the substrate surface, thus enabling individual manipulation and/or collective transfer to other target surfaces. Cyclic bending tests and finite element analysis (FEA) of the strain distribution further highlight the excellent mechanical deformability of a device layout consisting of μ-crystal pixels embedded in a polymeric matrix. Light-emitting diodes (LEDs) with individual InGaN/GaN μ-crystals exhibit strong electroluminescence (EL) with unique features such as variations in emission spectra with respect to crystal diameter and driving voltage bias. Comparative analyses of photoluminescence, cathodoluminescence, and electric potential simulation indicate a strong correlation between the EL wavelengths and dominant emitting regions of InGaN/GaN polyhedral crystal planes. This is further supported by scanning transmission electron microscopy of quantum well structures, which strongly depend on both size and the crystal facets.

Luminescence of K2BaCa(PO4)2: Ce3+, Tb3+ dual-emitting phosphor and its application as ratiometric optical thermometer

Abstract A new dual-emitting phosphor K2BaCa(PO4)2: Ce3+, Tb3+ (KBCP: Ce3+, Tb3+) was successfully synthesized and designed to put into application of ratiometric temperature sensing. Under single UV excitation, the developed phosphors shows both Ce3+ violet and Tb3+ green emission mainly at 360 and 542 nm, respectively. The Ce3+-Tb3+ energy transfer process was analyzed by the variation of emission spectra and Ce3+/Tb3+ decay lifetimes. The remarkable thermal stability has also been tested, indicating that the intensity at 200 °C is still above 85% of the original intensity. Furthermore, the emission intensity ratio between 360 and 542 nm of KBCP: Ce3+, Tb3+ is found to have a good linear relationship with temperature (R2 > 0.993), and the corresponding sensitivity temperature resolution is 0.35% K−1 and >0.02 K, respectively. Thus, this novel dual-emitting phosphor can be used as a potential luminescent thermometer.

BaLu6(Si2O7)2(Si3O10):Ce3+,Tb3+: A novel blue-green emission phosphor via energy transfer for UV LEDs

A series of novel blue-green emission phosphors BaLu6(Si2O7)2(Si3O10):Ce3+,Tb3+ (BLSO:Ce3+,Tb3+) were synthesized via the high-temperature solid-state reaction route. Many characterizations such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR) were conducted to analyze the phase and structure of as-prepared samples. Photoluminescence (PL) properties illustrated that Ce3+ singly doped BLSO can produce a broad band ranging from 365 to 550 nm upon UV excitation, which overlapped the excitation spectrum of Tb3+ monitored at 550 nm emission. Energy transfer phenomenon from Ce3+ to Tb3+ in this kind of phosphor was demonstrated from the variations of emission spectra and the decrease of Ce3+ fluorescent decay lifetime in Ce3+-Tb3+ co-doped BLSO, based on which the emission color can be tuned from bright blue to green upon UV excitation. The energy transfer mechanism from Ce3+ to Tb3+ was determined to be electric dipole-quadrupole interaction. Moreover, the temperature-dependent PL of representative BLSO:0.18Ce3+,1.00Tb3+ was supplied in this manuscript, which indicated the good thermal stability of this kind of phosphor. The results show that BLSO:Ce3+,Tb3+ phosphors can be as a potential candidate of blue-green component in phosphor-converted UV LEDs.

Photoluminescence and Energy Transfer Properties with Y+SiO4 Substituting Ba+PO4 in Ba3Y(PO4)3:Ce(3+)/Tb(3+), Tb(3+)/Eu(3+) Phosphors for w-LEDs.

A series of Ce(3+), Tb(3+), Eu(3+) doped Ba2Y2(PO4)2(SiO4) (BYSPO) phosphors were synthesized via the high-temperature solid-state reaction route. X-ray diffraction, high-resolution transmission electron microscopy, Fourier transform infrared, solid-state NMR, photoluminescence (PL) including temperature-dependent PL, and fluorescent decay measurements were conducted to characterize and analyze as-prepared samples. BYSPO was obtained by the substitution of Y+SiO4 for Ba+PO4 in Ba3Y(PO4)3 (BYPO). The red shift of PL emission from 375 to 401 nm occurs by comparing BYSPO:0.14Ce(3+) with BYPO:0.14Ce(3+) under 323 nm UV excitation. More importantly, the excitation edge can be extended from 350 to 400 nm, which makes it be excited by UV/n-UV chips (330-410 nm). Tunable emission color from blue to green can be observed under 365 nm UV excitation based on the energy transfer from Ce(3+) to Tb(3+) ions after codoping Tb(3+) into BYSPO:0.14Ce(3+). Moreover, energy transfer from Tb(3+) to Eu(3+) ions also can be found in BYSPO:Tb(3+),Eu(3+) phosphors, resulting in the tunable color from green to orange red upon 377 nm UV excitation. Energy transfer properties were demonstrated by overlap of excitation spectra, variations of emission spectra, and decay times. In addition, energy transfer mechanisms from Ce(3+) to Tb(3+) and Tb(3+) to Eu(3+) in BYSPO were also discussed in detail. Quantum yields and CIE chromatic coordinates were also presented. Generally, the results suggest their potential applications in UV/n-UV pumped LEDs.

Surface Effects on Photoluminescence and Optical Nonlinearity of CdS Quantum Dots Stabilized by Sulfonated Polystyrene in Water

A simple aqueous method has been used for the direct synthesis of water-soluble sulfonated polystyrene (SPS) encapsulated CdS quantum dots (QDs). The aqueous solution of the QDs, stabilized by two SPSs of different sulfonation level, shows a blue shift in ultraviolet–visible (UV–vis) absorption and band edge emission. High resolution transmission electron microscope (HR-TEM) establishes the presence of quantum confined CdS particles. The sulfonation level of SPS influences the size of QDs and strongly affects the photoluminescence (PL). The CdS QDs passivated by SPS with less sulfonation level exhibit only band edge emission (463 nm), while QDs in aqueous solution of SPS with high sulfonic acid content emits predominantly defect state emission (610 nm) against the band edge emission (463 nm). The PL of the SPS-CdS nanocomposites demonstrates an interesting variation in emission spectra and quantum yield via the change in sulfonation level, the change in pH and on keeping in aqueous solution. In addition, the z-scan measurements show negative nonlinear refraction coefficient, indicating self-defocusing phenomena. The absolute value of the third order nonlinear refractive index and nonlinear absorption are decided by the CdS QDs surface chemistry.

Change of Luminescence Properties of Europium Ions Captured by Mixed‐Ligand Silver Nanoparticles

AbstractWe present herein silver nanoparticles about 4 nm in diameter coated with a binary mixture of 1‐octanethiol and 2‐(2‐{2‐[(6‐mercaptohexyl)oxy]ethoxy}ethoxy)ethanol. These particles show an affinity towards optically active Eu3+ ions. The effect of the nanoparticle on the characteristic emission peaks of Eu3+ is investigated. We use the variation in emission spectra of the ion to establish its binding to the nanoparticles.

A new sensor for detection of CH3CN and ClCH2CN vapors based on vapoluminescent platinum(ii) complex

The planar platinum(II) complex [Pt(Me3SiC≡CbpyC≡CSiMe3)(C≡CC6H4Et-4)2] (1) with 5,5-bis(trimethylsilylethynyl)-2,2'-bipyridine was prepared and characterized. Solid-state 1 exhibits unusual, selective and reversible luminescence vapochromism to CH3CN and ClCH2CN vapors, which is useful for the detection of these hazardous vapors. A vapochromic cycle was monitored by dynamic variations in emission spectra and X-ray diffraction (XRD) patterns. Both X-ray crystallographic and density functional theory studies suggest that the vapochromic and vapoluminescent behavior of 1 are induced by the variation in the intermolecular Pt-Pt interactions.

IR spectral analysis for the diagnostics of crust earthquake precursors

Abstract. Some possible physical processes are analysed that cause, under the condition of additional ionisation in a pre-breakdown electric field, emissions in the infrared (IR) interval. The atmospheric transparency region of the IR spectrum at wavelengths of 7–15 μm is taken into account. This transparency region corresponds to spectral lines of small atmospheric constituents like CH4, CO2, N2O, NO2, NO, and O3. The possible intensities of the IR emissions observable in laboratories and in nature are estimated. The acceleration process of the electrons in the pre-breakdown electrical field before its adhesion to the molecules is analyzed. For daytime conditions, modifications of the adsorption spectra of the scattered solar emissions are studied; for nighttime, variations of emission spectra may be used for the analysis.

Mechanochromic Luminescence Switch of Platinum(II) Complexes with 5-Trimethylsilylethynyl-2,2′-bipyridine

Planar platinum(II) complexes Pt(bpyC≡CSiMe(3))(C≡CC(6)H(4)R-4)(2) (R = H (1), Bu(t) (2)) with 5-trimethylsilylethynyl-22'-bipyridine show an unusual, reversible, and reproducible mechanical stimuli-responsive color and luminescence switch. When crystalline 1 or 2 is ground, bright yellow-green emitting is immediately converted to red luminescence with an emission red shift of 121-155 nm for 1 or 53-89 nm for 2. Meanwhile, the crystalline state is transformed to an amorphous phase that can be reverted to the original crystalline state by organic vapor adsorbing or heating, along with red luminescence turning back to yellow-green emitting. The reversibility and reproducibility of luminescence mechanochromic properties have been dynamically monitored by the variations in emission spectra and X-ray diffraction patterns. The drastic grinding-triggered emission red shift is likely involved in the formation of a dimer or an aggregate through Pt-Pt interaction, resulting in a conversion of the (3)MLCT/(3)LLCT emissive state in the crystalline state into the (3)MMLCT triplet state in the amorphous phase. Compared with the drastic grinding-triggered emission red shift in 1 (121-155 nm), the corresponding response shift in 2 (53-89 nm) is much smaller since a bulky tert-butyl in C≡CC(6)H(4)bu(t)-4 induces the planar platinum(II) molecules to stack through a longer Pt-Pt distance and less intermetallic contact compared with that in 1, as suggested from EXAFS studies.

Vapor‐ and Mechanical‐Grinding‐Triggered Color and Luminescence Switches for Bis(σ‐fluorophenylacetylide) Platinum(II) Complexes

Square-planar bis(σ-fluorophenylacetylide) platinum(II) complexes [Pt(Me(3)SiC≡CbpyC≡C-SiMe(3))(C≡CC(6)H(4)F)(2)] (C≡CC(6)H(4)F-2 for 2, C≡CC(6)H(4)F-3 for 3, and C≡CC(6)H(4)F-4 for 4; Me(3)SiC≡CbpyC≡CSiMe(3)=5,5'-bis(trimethylsilylethynyl)-2,2'-bipyridine) were prepared and were characterized by spectroscopic and luminescence studies, and X-ray crystallography. The color and luminescence of crystalline complex 3 is specifically sensitive to CHCl(3) vapor to afford 140-180 nm of luminescence vapochromic redshift, which is useful for specific detection of CHCl(3) vapor. Complex 4 displays selective luminescence vapochromic properties to CH(2)Cl(2) and CHCl(3) vapors with a luminescence vapochromic shift response of ca. 150-200 nm. Interestingly, complexes 2-4 exhibit reversible, and naked-eye perceivable, mechanical stimuli-responsive color and luminescence changes. When solid species 2-4 are crushed gently or ground, the crystalline state is converted to an amorphous phase. Meanwhile, bright yellow-orange luminescence in the crystalline species is converted to dark red under UV light irradiation with 100-160 nm of mechanochromic shift response. A vapochromic or mechanochromic cycle was monitored by dynamic variations in emission spectra and X-ray diffraction (XRD) patterns. The halohydrocarbon vapor- or mechanical-grinding-triggered color and luminescence switches are most likely correlated to a shorted intermolecular Pt-Pt distance as that revealed in vapochromic species 4·0.5 CH(2)Cl(2) by X-ray crystallography, thus leading to an increased contribution from intermolecular Pt-Pt interaction as demonstrated by DTF computational studies.

The problem of dating quartz 1: Spectroscopic ionoluminescence of dose dependence

A suite of quartz samples of different provenances, irradiation, thermal and depositional histories were analysed using spectroscopic ionoluminescence (IL) to investigate variations in emission spectra as a function of cumulative radiation dosing. Protons were selected for implantation to mimic the effect of natural radiation over geological timescales. All samples exhibited depletion in the UV–violet emission (3.2–3.4 eV) with increasing cumulative dose, whilst the red emission (1.8–1.9 eV) increased. A power–law relationship exists between the two emissions. It is inferred that the luminescence emission of quartz is indicative of its radiation history, and spectral analyses could be used to determine the utility of different quartz samples for optically stimulated luminescence dating (OSL) where the detection range is limited to 3.4–4.6 eV.

Temperature and excitation intensity tuned photoluminescence in Tl4GaIn3S8 layered single crystals

AbstractPhotoluminescence spectra of Tl4GaIn3S8 layered crystals grown by Bridgman method have been studied in the wavelength region of 500–780 nm and in the temperature range of 26–130 K with extrinsic excitation source (λexc = 532 nm), and at T = 26 K with intrinsic excitation source (λexc = 406 nm). Three emission bands A, B and C centered at 514 nm (2.41 eV), 588 nm (2.11 eV) and 686 nm (1.81 eV), respectively, were observed for extrinsic excitation process. Variations in emission spectra have been studied as a function of excitation laser intensity in the 0.9‐183.0 mW cm–2 range for extrinsic excitation at T = 26 and 50 K. Radiative transitions from the donor levels located at 0.03 and 0.01 eV below the bottom of the conduction band to the acceptor levels located at 0.81 and 0.19 eV above the top of the valence band were proposed to be responsible for the observed A‐ and C‐bands. The anomalous temperature dependence of the B‐band peak energy was explained by configurational coordinate model. From X‐ray powder diffraction and energy dispersive spectroscopic analysis, the monoclinic unit cell parameters and compositional parameters of Tl4GaIn3S8 crystals were determined, respectively. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Below and above bandgap excited photoluminescence inTl4InGa3S8 layered single crystals

Photoluminescence (PL) spectra ofTl4InGa3S8 layered single crystals grown by the Bridgman method have been studied in the550–710 nm wavelength and 80–300 K temperature ranges with below bandgap excitation(λexc = 532 nm),and in the 420–600 nm wavelength and 30–300 K temperature ranges with above bandgap excitation(λexc = 325 nm). The broad emission bands centered at 580 nm (2.14 eV) and 496 nm (2.49 eV) were observed atT = 80 and 30 K for below and above bandgap excitation processes, respectively. Variations inemission spectra have been studied as a function of excitation laser intensity in the10.3–429.7 mW cm−2 range for below bandgap excitation. Radiative transitions from the donor levels located at0.02 and 0.37 eV below the bottom of the conduction band to the deep acceptor levellocated at 0.20 eV above the top of the valence band were proposed to be responsible forthe observed PL bands. From x-ray powder diffraction and EDS analysis, themonoclinic unit cell parameters and compositional parameters, respectively, weredetermined.

Autofluorescence quantifies collagen in sausage batters with a large variation in myoglobin content

In order to clarify the potential of the method of autofluorescence for determining the collagen content in meat batter, an experimental design was used where the emission originating from collagen was unrelated to the effect of myoglobin absorbance on the emission spectra. Muscles like beef Masseter, beef Latissimus dorsi and pork Glutens medius assured a large variation in myoglobin content, and made absorbance from myoglobin account for 65–84% of the variation in the emission spectra at wavelengths normally thought interesting for collagen quantification. Collagen (range 1.3–4.0%) accounted for 7–18% of the variation in the autofluorescence emission spectra. Collagen content could be predicted from the emission spectra provided multivariate regression techniques were used. Pre-processing of spectra reduced the prediction error for collagen by 0.03–0.12%, depending on method used; the lowest prediction error obtained being 0.48%. The method of autofluorescence gave lower prediction errors for collagen content than did the method of near infrared reflectance when applied to the same batters.

The Effect of Temperature and Excitation on the Single- and Two-Photon Excited Emission Spectrum of Curium in a Glass Matrix

Single and two-photon excited emission has been observed from a curiumdoped borosilicate glass matrix at both room and liquid nitrogen temperatures. The emission spectrum was measured using several different excitation energies and intensities. In addition to the expected line narrowing, variations in the ratios of emission intensities between states, and between crystal field levels within the each state were observed with cooling. Slight variations in the emission spectrum also arose as a function of the excitation intensity. These variations in the Cm ion's emission spectrum as a function of experimental parameters are presented and discussed.

Variations in emission spectrum over southern radio sources of large angular extent

Sixteen extragalactic sources of large angular extent have been observed at 5000 MHz with the Parkes 64-m telescope (FWHP 4 arcmin). The structures are compared with those determined at 408 MHz from the Molonglo Cross telescope (FWHP 3 arcmin), and in several cases spectral variations over the sources are apparent. In a discussion extending the comparison to other sources for which similar observations are available, we show that spectral variations occur more frequently (but not exclusively) in the sources with lower luminosity, and that the nature of the variation depends on luminosity.