Observed Emission Peaks Research Articles

Physical, optical and spectral properties of Sm3+ and Eu3+ ions doped zinc boro-phosphate glass

This study focuses on the synthesis of Sm³⁺ and Eu³⁺ rare earth ions doped zinc boro-phosphate glasses and their physical, optical and spectral characterization. Photoluminescence was carried out through both steady-state and time-domain luminescence measurements. The glasses were prepared via the melt quenching technique, and they exhibit impressive mechanical strength and transparency. Judd-Ofelt analysis of the near-infrared absorption spectra revealed parameters Ω₂, Ω₄, and Ω₆, indicating low covalency and reduced site asymmetry for the rare earth ions compared to those in silicate-based glasses. When excited with violet light, the Sm³⁺-doped samples emitted bright orange luminescence, resulting from radiative relaxation from the ⁴G₅/₂ state to lower energy levels. The calculated branching ratios correspond well with the observed emission peak ratios. However, increasing the Sm³⁺ ion concentration resulted in reduced luminescence intensity and shorter fluorescence lifetimes, due to cross-relaxation effects. In the Sm³⁺/Eu³⁺ co-doped glasses, energy transfer from Sm³⁺ to Eu³⁺ ions was detected upon selective excitation of Sm³⁺ ions. This energy transfer efficiency was found to increase with higher concentrations of Eu³⁺ ions.

Visible room-temperature emission and excitation photoluminescence in In+- and As+-co-implanted SiO2 films

The visible room-temperature emission and excitation photoluminescence spectra were studied as a function of the indium and arsenic profiles in the In+ and As+ ion-implanted thermally grown SiO2 films before and after the annealing at the temperature of 900 °C. As+ ions at the energy of 40 or 135 keV and In+ ions at the energy of 50 keV, providing a projective range ratio RpAs/RpIn of 1 or 3, respectively, were used. Four emission photoluminescence bands, peaked at ∼347 nm (3.57 eV), ∼440 nm (2.81 eV), ∼450 nm (2.75 eV) and ∼500 nm (2.48 eV), were obtained from the 40 keV As+ and 50 keV In+ ion-implanted samples under the excitation wavelength of 300 nm (4.13 eV), 350 nm (3.54 eV), 400 nm (3.10 eV) and 450 nm (2.75 eV), respectively. As the As+ energy increased to 135 keV, under the same excitation conditions, the emission bands peaked at 370 nm (3.35 eV), 420 nm (2.95 eV), 460 nm (2.69 eV) and 505 nm (2.45 eV) dominated in the photoluminescence spectra. The excitation spectra of the observed emission peaks were studied, too. We preliminarily interpret the observed photoluminescence peaks as a result of the T1 → S0 transition of molecular-like clusters associated with the oxygen deficiency provided by In or In–As in ion-implanted SiO2.

Fabrication of Detonation Nanodiamonds Containing Silicon‐Vacancy Color Centers by High Temperature Annealing

Detonation nanodiamonds (DNDs) with sizes below 10 nm have attracted attention as single photon emitters with potential in many research fields from life sciences to quantum technologies. However, while nitrogen‐vacancy (NV) color centers are found in nanodiamonds directly after the detonation synthesis without the need for irradiation or annealing, silicon‐vacancy (SiV) color centers are not present in these pristine samples. Herein, SiV centers are created in DNDs by an annealing treatment up to 1100 °C in high vacuum. As silicon is not added, the precursor of the SiV centers must be pristine silicon impurities inside the nanodiamond lattice. A sharp emission line at the wavelength of 737 nm with a linewidth of 7.7 nm is observed in DNDs that are electron irradiated before annealing. This wavelength is consistent with the characteristic emission line of SiV centers and its linewidth is comparable with that in larger nanodiamonds created by chemical vapor deposition and subsequent milling. The average lifetime (0.4 ± 0.04 ns) of the fluorescence, which is in the range of reported lifetimes in nanodiamonds, also support that the observed emission peak are due to SiV centers in DNDs.

Photo-, radio- and thermo- luminescence properties of Eu-doped BaSi2O5 glass-ceramics

The optical, radioluminescence and thermoluminescence properties of Eu-doped BaSi2O5 glass-ceramics were evaluated. The glass samples were synthesized by the conventional melt-quenching technique using a carbon crucible under reductive condition and heat-treated at different temperatures. The samples exhibit photoluminescence and radioluminescence with a broad emission due to Eu2+, and the observed emission peaks are blue-shifted in the crystallized samples. The decay time constants are the typical values of the 5d-4f transitions of Eu2+. The glass sample shows no clear thermoluminescence glow peak while the glass-ceramic samples show an intense thermoluminescence glow peak around 180 °C. The thermoluminescence intensity monotonically increases with the irradiated X-ray dose, which covers from 0.01 to 1000 mGy.

Characterizations of Pr-doped Yb3Al5O12 single crystals for scintillator applications

Yb3Al5O12 (YbAG) single crystals doped with different concentrations of Pr were synthesized by the Floating Zone (FZ) method. Then, we evaluated their basic optical and scintillation properties. All the samples showed photoluminescence (PL) with two emission bands appeared approximately 300–500 nm and 550–600 nm due to the charge transfer luminescence of Yb3+ and intrinsic luminescence of the garnet structure, respectively. A PL decay profile of each sample was approximated by a sum of two exponential decay functions, and the obtained decay times were 1 ns and 3–4 ns. In the scintillation spectra, we observed emission peaks in the ranges from 300 to 400 nm and from 450 to 550 nm for all the samples. The origins of these emissions were attributed to charge transfer luminescence of Yb3+ and intrinsic luminescence of the garnet structure, respectively. The scintillation decay times became longer with increasing the Pr concentrations. Among the present samples, the 0.1% Pr-doped sample showed the lowest scintillation afterglow level. In addition, pulse height spectrum of 5.5 MeV α-rays was demonstrated using the Pr-doped YbAG, and we confirmed that all the samples showed a full energy deposited peak. Above all, the 0.1% Pr-doped sample showed the highest light yield with a value of 14 ph/MeV under α-rays excitation.

Effect of the carrier gas on morphological, optical and electrical properties of SnO2 nanostructures prepared by vapor transport

The aim of the study was to explore the effects of carrier gas on the properties of SnO2 nanostructures grown by vapor transport method for possible optoelectronic applications. Nanostructures of SnO2 were synthesized via vapor transport method using Ar plus O2 and N2 plus O2 gas mixtures. It was found that the carrier gas (Ar or N2) has great influences on the properties of the resulting SnO2 nanostructures. Tetragonal single phase SnO2 with nanowires (NWs) morphologies was obtained for Ar/O2. The diameters of the NWs ranged from 10 to 162 nm and the lengths exceed 5 µm. While tetragonal single phase SnO2 with nanoparticles morphologies (diameters of 42–173 nm) was obtained for N2/O2. The calculated optical band gap values were 3.81 and 2.95 eV for samples prepared with Ar/O2 and N2/O2, respectively. The conduction mechanism in the samples was found to be thermally activated. Single activation energy of 0.49 eV was evaluated for the sample prepared in Ar/O2, while two activation energies (EAL = 1.48 eV and EAh = 0.83 eV) were obtained for the sample prepared with N2/O2. The photoluminescence emission (intensity and shape) depended on the carrier gas. The observed emission peaks were assigned to the oxygen vacancies and the oxygen related defects. The obtained results may find applications in optoelectronics such as light emitting diodes.

Spin-coated Al-doped ZnO thin films for optical applications: Structural, micro-structural, optical and luminescence studies

Zn1−xAlxO (x = 0, 0.01, 0.02, 0.03) thin films were deposited on glass substrate using sol-gel spin coating method and the effect of Al doping on their structural, micro-structural, optical and photoluminescence properties were investigated. The XRD results confirm the single phase nature and the successful substitution of Al at Zn site in ZnO thin films. Further with Al doping, the crystallite size, lattice parameters and film thickness were found to decrease. Also, both AFM and SEM results confirm the formation of spherical grains with lower roughness of the films. Al doped (>2%) films shows ∼ 90% transparency in the visible wavelength region. Widening of band gap (3.18–3.34 eV) was observed with increase in Al doping concentration, which was attributed to the Burstein–Moss band-filling effect. The defect induced luminescence at room temperature was studied by photoluminescence spectroscopy. PL spectra of AZO films show sharp peaks in the visible wavelength region. A detailed analysis of photoluminescence of undoped and Al doped ZnO films indicates the inhibition of defect density of electronic states due to substitution of Al3+. The observed emission peaks were attributed to the defect related deep-level emissions. Results suggest possible use of Al doped ZnO films for transparent conducting oxide (TCO) electrodes and light emitting diodes (LED's) applications.

Up-conversion luminescence of novel Yb^3+-Ho^3+/Er^3+ doped Sr_5(PO_4)_3Cl phosphors for optical temperature sensing

To explore new phosphor materials for optical temperature sensors, the Yb3+-Ho3+ and Yb3+-Er3+ doped Sr5(PO4)3Cl (SPC) phosphors were prepared by the solid-state reaction method, and their upconversion luminescence properties were investigated. Upon 980 nm excitation, three emission peaks around 543, 668, and 758 nm are found for SPC:Yb3+,Ho3+, which could be attributed to the typical Ho3+ transitions. For the SPC:Yb3+,Er3+ phosphor, the dominant emission peak is located around 673 nm and the green emission peaks are very weak. By studying the dependence of intensities on the excitation powder, all the observed emission peaks for Yb3+-Ho3+ and Yb3+-Er3+ doped SPC samples are two-photon processes. The temperature-dependence measurement reveals that the fluorescence intensity ratios of 668/543 nm emissions for Ho3+ and 522/544 nm emissions for Er3+ change with the temperature. The reason has been interpreted by the energy level diagram, decay curves and so on. The sensitivity of the present samples were evaluated with the temperature changed from 293 to 553 K, and the high sensitivities have been obtained.

Biosynthesis and Photocatalytic Properties of SnO2 Nanoparticles Prepared Using Aqueous Extract of Cauliflower

This work reports the biosynthesis of Sn(OH)2 using aqueous extract of fresh cauliflower (Brassica oleracea L. var. botrytis), and the subsequent preparation of SnO2 nanoparticles at two different annealing temperatures of 300 and 450 °C for 2 h. The obtained SnO2 nanoparticles were denoted as S1 and S2 for the samples prepared at 300 and 450 °C, respectively. XRD analysis identified rutile tetragonal phase of SnO2 nanoparticles and TEM results gave a quasispherical and spherical morphologies for S1 and S2 respectively of the size range 3.62–6.34 nm. The optical properties were studied with UV–vis and photoluminescence (PL) spectroscopies, and the nanoparticles showed blue shift in their absorption edges. The observed emission peak in the PL spectra found around 419 nm is attributable to oxygen vacancies and defects. Photocatalytic activities of the nanoparticles (S1 and S2) were studied using methylene blue (MB) under ultraviolet light irradiation and the results reveal 91.89 and 88.23% degradation efficiency of MB by S1 and S2 respectively over a period of 180 min.

Fabrication and characterization of SiO2@SiC shell–core nanowire prepared by laser sintering

One-dimensional SiO2@SiC shell–core nanowire was fabricated on a SiC substrate without any catalyst using a laser sintering method. Based on a solid–liquid–vapor–solid (SLVS) in situ growth mechanism, the as-synthesized SiO2@SiC nanowires of about 60 nm diameter with a shell thickness of about 13 nm were grown. Varying the power density of laser sintering allowed the final SiC particle morphology to be controlled from grainy to whisker-like. High power density or high temperature benefited the nucleation probability of SiC whiskers. The isothermal oxidation test showed that the SiO2@SiC nanowires have good thermodynamic stability at high temperature. The photoluminescence (PL) property of SiO2@SiC nanowire was also investigated. The observed emission peaks were composed of an UV peak centered at 365 nm (3.40 eV) and a blue peak centered at 453 nm (2.74 eV). The theory behind the PL property and the growth mechanism of the SiO2@SiC nanowire were also discussed.

Theoretical Study of Optical Properties of Native Point Defects in α-Al2O3

Using first-principles calculations based on density functional theory with generalized gradient approximation (GGA) parameterized by Perdew-Burke-Ernzerhof (PBE) for the exchange-correlation functional, we studied the native point defects in α-Al2O3. We found that oxygen vacancy (VO), Al vacancy (VAl), and Al interstitial (Ali) are the dominant defects in α-Al2O3 under both Al- and O-rich growth conditions. Because the optical properties of α-Al2O3 are important for many device applications, the optical excitation levels due to these native point defects were studied. Our results revealed that the absorption and emission bands at ∼3.0 and 6.0 eV should be associated with VO (F-center) in good agreement with previous works. Moreover, the observed emission peak at ∼3.8 eV is very close to the calculated emission energy of Ali. The absorption and emission due to other native point defects were also reported.

Electroluminescence from Cr3+ in Perovskite Thin-Film Phosphors Using LaAlO3 and LaGaO3 as Hosts

We observed multicolor and near-infrared electroluminescence (EL) from perovskite oxide thin-film phosphors using Cr- and Ce-co-doped LaGaO3 and LaAlO3. These phosphor thin films were prepared by varying either Cr or Ce content using a combinatorial r.f. magnetron sputtering deposition method. Intense deep-red and weak yellow-green EL emissions were observed from thin-film electroluminescent (TFEL) devices fabricated using posannealed LaGaO3:Ce,Cr thin films. Intense near-infrared emission and yellow-green EL emissions were observed from TFEL devices fabricated using posannealed LaAlO3:Ce,Cr thin films. The highest EL intensity was obtained in TFEL devices using postannealed LaGaO3:Ce,Cr and LaAlO3:Ce,Cr phosphor thin films with Cr content approximetly 3 and 1at.%, respectively. All the observed emission peaks in EL from the LaGaO3:Ce,Cr and/or the LaAlO3:Ce,Cr phosphor thin films were assigned to either the emission originating from the transition in the Ce3+ and Cr3+ ions.

Electrically driven light emission from a single suspended carbon nanocoil

Electrically driven thermal radiation spectra from single suspended carbon nanocoils (CNCs) were investigated. The suspended CNC, whose structure is a hybrid between sp2 graphite-like nanocrystallites and sp3 amorphous carbon, shows thermally excited emission peaks superimposed on the blackbody radiation spectrum for wavelengths above 600nm. It is believed that at least four pairs of energy bands exist around the Fermi energy level and the observed emission peaks are attributed to thermally-excited interband electron transitions in the CNC. Photoluminescence measurements for the CNCs show similar emission peaks to the thermally excited emission, which further supports our speculation on the electronic structure of the CNC.

Observation of red emission in wurtzite ZnS nanoparticles and the investigation of phonon modes by Raman spectroscopy

Wurtzite ZnS nanoparticles are synthesized by a low temperature chemical method using ethylene glycol. Photoluminescence studies reveal a new red emission along with strong UV and blue emission known to occur from nanocrystalline ZnS. An energy level diagram involving oxygen trap levels and interstitial sulphur ions is proposed to explain the origin of the observed emission peaks. Micro-Raman spectroscopic studies indicate that the optic modes get softened whereas the second order longitudinal acoustic (LA) phonon mode get hardened in the nanocrystals. The analysis is done by taking into account the effect of the small particle size of nanoparticles as well as the existence of defects resulting in strain in the lattice.

Preparation and Photoluminescence Properties of Eu2+-Doped Oxyapatite-Type SrxLa10−x (SiO4)6O3−x/2

Eu2+-doped oxyapatite SrxLa10−x(SiO4)6O3−x/2 phosphors are prepared by solid-state reaction at high temperatures under reducing atmosphere. Their crystal structures and photoluminescence are investigated by x-ray diffraction (XRD) and fluorescence spectroscopy, respectively. The XRD results indicate that the samples are pure oxyapatite phase (P63/m space group). The fluorescence spectra show two peaks corresponding to two sites (4f and 6h sites) for Eu2+ in the host lattice. As the Eu2+ content influences the intensity ratio of the two observed emission peaks, the photoluminescence mechanism is discussed.

Unprecedentedly Strong and Narrow Electromagnetic Emissions Stimulated by High-Frequency Radio Waves in the Ionosphere

Experimental results of secondary electromagnetic radiation, stimulated by high-frequency radio waves irradiating the ionosphere, are reported. We have observed emission peaks, shifted in frequency up to a few tens of Hertz from radio waves transmitted at several megahertz. These emission peaks are by far the strongest spectral features of secondary radiation that have been reported. The emissions are attributed to stimulated Brillouin scattering, long predicted but hitherto never unambiguously identified in high-frequency ionospheric interaction experiments. The experiments were performed at the High-Frequency Active Auroral Research Program (HAARP), Alaska, USA.

Optical absorption and emission properties of Pr 3+ and Er 3+ in lithium cesium mixed alkali borate glasses

This article presents the optical absorption and emission properties of Pr 3+ and Er 3+ in mixed alkali borate glasses of the type 68B 2O 3· xLi 2O·(32- x)Cs 2O (where x = 8 , 12, 16, 20 and 24). The variation of Judd–Ofelt intensity parameters ( Ω λ ), the peak wavelength of the hypersensitive transitions, radiative transition probabilities ( A rad) and peak emission cross-sections ( σ p) with x in the glass matrix have been discussed in detail. The changes in position of hypersensitive transition and intensity parameters with x are correlated to the structural changes in the host matrix. The estimated radiative lifetimes ( τ R) of certain excited states of both Pr 3+ and Er 3+ in lithium cesium mixed alkali borate glasses are reported. Branching ratios ( β) and integrated absorption cross-sections ( Σ) for certain important transitions are presented. Peak stimulated emission cross-sections ( σ p) are calculated for the observed emission peaks of Pr 3+ and Er 3+ ions in this glass matrix.

The I*(2P1/2)−I*(2P1/2) Contact Pair Emission in Condensed Media: A Molecular Spring-Gauge for Cavity Sizing

The I*I*(0g + ) f I*I(B(0u + )) emission spectra obtained in neat Ar, Kr, Xe, and in mixed Kr/Xe matrixes is reported. The emission from the strictly cage-bound initial state shifts linearly with Kr/Xe mixing fraction, without significant change in spectral width. The line shapes in mixed-hosts are understood in terms of the statistics of sites in the solid solutions. The pure-host line shapes are reproduced through Monte Carlo simulations using accurately known I-Rg potentials. The analysis yields a refined I*I* potential and provides a calibration curve to readout the cavity size of isolation from the observed emission peak shift.

STM light emission from Si([formula omitted])[formula omitted]-Ag surface

Light emission stimulated by scanning tunneling microscope (STM-LE) from a Si(111)3×3-Ag surface was studied by a light detection system combined with a UHV-STM. A single broad peak appears in the emission (fluorescence) spectra and the peak energy linearly shifts to higher energies with increasing bias voltage. Photon maps clearly reveal the steps between the hole–island pairs in the Si(111)3×3-Ag surface, and those steps show dark contrast for the positive bias voltage and bright contrast for the negative bias voltage, respectively. The Si(111) 7×7 and Si(111)3×3-Ag regions show a clear contrast in the photon map, which indicates that the STM-LE is sensitive to the surface structure. The STM-LE from Si(111)3×3-Ag is well understood from the inverse photoemission process or inelastic tunneling process. The observed emission peak can be attributed to the transition of electrons near the Fermi level in the tungsten tip to the surface state of Si(111)3×3-Ag reported by the inverse photoemission measurement.

Separation of Dielectric Nonideality from Preferential Solvation in Binary Solvent Systems: An Experimental Examination of the Relationship between Solvatochromism and Local Solvent Composition around a Dipolar Solute

Dielectric nonideality of a binary solvent system refers to the deviation of the Onsager reaction field function from linearity in the polar mole fraction of the solvent mixture. A dipolar fluorophore dissolved in an ideal dielectric mixture exhibits a solvatochromic shift that is linear in the solvent polar mole fraction in it's solvation sphere. As a result, the “local composition” can be easily determined from the peak shift. Here we identify the conditions under which this linear approximation is appropriate for estimating local compositions around dipolar solutes. In a previous study (Khajehpour, M. H.; Kauffman, J. F. J. Phys. Chem. A 2000, 104, 7151−7159), we have demonstrated the influence of dielectric nonideality on the observed emission peak shifts of the charge-transfer excited state of ADMA [1-(9-anthryl)-3-(4-N,N-dimethylaniline)propane] in hexanes−ethanol mixtures. The linear approximation fails for this binary solvent, and a more elaborate method of analysis such as Suppan's nonlinearity ratio method must be used to determine the local composition from solvatochromic shifts. In this work, we examine mixture nonideality and dielectric enrichment in hexane−tetrahydrofuran and hexane−dichloromethane mixtures. Our analysis demonstrates that the contribution of nonideality to the observed solvatochromic shifts cannot be neglected in these binary solvents. Using Suppan's theory of dielectric enrichment, we have calculated the local composition of ADMA's solvation sphere and find that it is enriched in the polar component by ∼30% over the bulk composition. This calculated value agrees with experimental measures of the local composition based on analysis of solvatochromic shifts using Suppan's nonlinearity ratio method which accounts for dielectric nonideality. The linear approximation overpredicts this composition by as much as 50%, even though these binary solvents are more nearly ideal than the hexane−ethanol system. Following this observation, we have identified conditions under which the linear approximation is justified, and find that for most cases of practical importance the linear approximation will not provide accurate estimates of the local solvent composition from solvatochromic studies. Similarly, solvatochromic shifts can only be accurately predicted from theoretical local compositions if dielectric nonideality is taken into account. These results along with our previous studies indicate that the charge-transfer excited state of ADMA behaves as an ideal dipolar solute.