Showing papers on "Photoluminescence excitation published in 2012"
TL;DR: The zero-phonon transition rate of a nitrogen-vacancy center is enhanced by a factor of ∼70 by coupling to a photonic crystal resonator fabricated in monocrystalline diamond using standard semiconductor fabrication techniques.
Abstract: The zero-phonon transition rate of a nitrogen-vacancy center is enhanced by a factor of ∼70 by coupling to a photonic crystal resonator fabricated in monocrystalline diamond using standard semiconductor fabrication techniques. Photon correlation measurements on the spectrally filtered zero-phonon line show antibunching, a signature that the collected photoluminescence is emitted primarily by a single nitrogen-vacancy center. The linewidth of the coupled nitrogen-vacancy center and the spectral diffusion are characterized using high-resolution photoluminescence and photoluminescence excitation spectroscopy.
425 citations
TL;DR: Important features in the spectral and temporal photoluminescence excitation of single nitrogen-vacancy centers in diamond are reported at conditions relevant for quantum applications.
Abstract: Important features in the spectral and temporal photoluminescence excitation of single nitrogen-vacancy (NV) centers in diamond are reported at conditions relevant for quantum applications. Bidirectional switching occurs between the neutral (NV(0)) and negatively charged (NV(-)) states. Luminescence of NV(-) is most efficiently triggered at a wavelength of 575 nm which ensures optimum excitation and recharging of NV(0). The dark state of NV(-) is identified as NV(0). A narrow resonance is observed in the excitation spectra at 521 nm, which mediates efficient conversion to NV(0).
164 citations
TL;DR: The results provide conclusive evidence that the photoluminescence in gold nanostructures indeed occurs via radiative damping of plasmon resonances driven by excited electrons in the metal itself.
Abstract: In this work, we performed a systematic study on the photoluminescence and scattering spectra of individual gold nanostructures that were lithographically defined. We identify the role of plasmons in photoluminescence as modulating the energy transfer between excited electrons and emitted photons. By comparing photoluminescence spectra with scattering spectra, we observed that the photoluminescence of individual gold nanostructures showed the same dependencies on shape, size, and plasmon coupling as the particle plasmon resonances. Our results provide conclusive evidence that the photoluminescence in gold nanostructures indeed occurs via radiative damping of plasmon resonances driven by excited electrons in the metal itself. Moreover, we provide new insight on the underlying mechanism based on our analysis of a reproducible blue shift of the photoluminescence peak (relative to the scattering peak) and observation of an incomplete depolarization of the photoluminescence.
153 citations
TL;DR: In this paper, the crystalline phase of the doped and undoped nanoparticles and particle sizes are observed with X-ray diffraction and transmission electron microscope, and FTIR confirms the bonding interaction of Co 2+ in TiO 2 lattice framework.
133 citations
TL;DR: Pressure-dependences of X-ray diffraction and photoluminescence from alkane-terminated colloidal particles are reported, and the diamond-phase bulk modulus is determined, and a systematic photolumscence red shift is found that matches the X(conduction)-to-Γ(valence) transition of bulk crystalline silicon.
Abstract: A lack of consensus persists regarding the origin of photoluminescence in silicon nanocrystals Here we report pressure-dependences of X-ray diffraction and photoluminescence from alkane-terminated colloidal particles We determine the diamond-phase bulk modulus, observe multiple phase transitions, and importantly find a systematic photoluminescence red shift that matches the Xconduction-to-Γvalence transition of bulk crystalline silicon These results, reinforced by calculations, suggest that the efficient photoluminescence, frequently attributed to defects, arises instead from core-states that remain highly indirect despite quantum confinement
130 citations
TL;DR: In this paper, the intrinsic absorption and photoluminescence spectra of rubrene single crystals were derived from a series of experiments performed at different excitation wavelengths and in different experimental geometries.
Abstract: We report the intrinsic absorption and photoluminescence spectra of rubrene single crystals, deriving them from a series of experiments performed at different excitation wavelengths and in different experimental geometries. We describe the absorption spectra for all three light polarizations in the crystal, and discuss how anisotropic wavelength-dependent absorption and emission affect the characteristics of observed photoluminescence spectra. We identify vibronic progressions both in absorption and emission and discuss their parameters and the main vibrational modes that are responsible for them. We propose that the most commonly measured absorption and emission in rubrene, the one with light polarization perpendicular to the $c$ axis of the crystal, is caused by vibronic-induced depolarization of the $c$-polarized electronic transition between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO).
107 citations
TL;DR: In this paper, structural and spectroscopic characterizations of the samples have been performed by X-ray diffraction and photoluminescence spectra measurements and the optimal Ce3+ dopant concentrations in both compounds were determined, and the concentration quenching mechanisms were also discussed.
Abstract: Ce3+-doped Ba2Ln(BO3)2Cl (Ln = Gd, Y) phosphors were synthesized through a conventional high-temperature solid state method in CO atmosphere. Structural and spectroscopic characterizations of the samples have been performed by X-ray diffraction and photoluminescence spectra measurements. The phosphors can be efficiently excited by near ultraviolet (n-UV) light resulting in blue emission. The optimal Ce3+ dopant concentrations in both compounds were determined, and the concentration quenching mechanisms were also discussed. The photoluminescence excitation (PLE) and emission (PL) spectra, and decay curves at liquid helium temperature were measured to analyze the crystallographic occupancy sites of Ce3+ in the Ba2Ln(BO3)2Cl (Ln = Gd, Y) hosts. The thermal stabilities of the phosphors Ba2Ln(BO3)2Cl:Ce3+ (Ln = Gd, Y) were studied using the dependence of the luminescence intensities on temperature (300–500 K), and their luminescence quenching temperatures and thermal activation energies were also determined. The results indicate that the phosphor Ba2Gd(BO3)2Cl:Ce3+ offers excellent optical properties as a potential blue-emitting phosphor candidate for n-UV LEDs, such as a higher thermal stability and a stronger luminescence intensity, than those of the phosphor Ba2Y(BO3)2Cl:Ce3+.
94 citations
TL;DR: A first consistent model for the understanding of multiphoton photoluminescence generation in gold nanoantennas is provided, opening new perspectives for applications ranging from the characterization of plasmonic resonances to biomedical imaging.
Abstract: Two-pulse correlation is employed to investigate the temporal dynamics of both two-photon photoluminescence (2PPL) and four-photon photoluminescence (4PPL) in resonant and nonresonant nanoantennas excited at a wavelength of 800 nm. Both 2PPL and 4PPL data are consistent with the same two-step model already established for 2PPL, implying that the first excitation step in 4PPL is a three-photon sp → sp direct interband transition. Considering energy and parity conservation, we also explain why 4PPL behavior is favored over, for example, three- and five-photon photoluminescence in the power range below the damage threshold of our antennas. Since sizable 4PPL requires larger peak intensities of the local field, we are able to select either 2PPL or 4PPL in the same gold nanoantennas by choosing a suitable laser pulse duration. We thus provide a first consistent model for the understanding of multiphoton photoluminescence generation in gold nanoantennas, opening new perspectives for applications ranging from the characterization of plasmonic resonances to biomedical imaging.
85 citations
TL;DR: In this article, the photoluminescence properties of the samples were investigated by excitation and emission spectra, and it was shown that the samples have broad blue excitation band located at 430-510nm, which covers the emission wavelength of commercial blue light-emitting diode (LED) chips.
76 citations
TL;DR: In this paper, the as-synthesized Ca3−xB2O6:xDy3+ (0.95−yDy0.34) phosphors were synthesized at 1100°C in air by solid-state reaction route.
72 citations
TL;DR: In this article, the fabrication and photoluminescence properties of colloidal SiC quantum dots stemming from diminishing different polytypes (3C, 6H, and 4H) of bulk SiC crystals using electrochemical method were reported.
Abstract: We report the fabrication and photoluminescence properties of the colloidal SiC quantum dots (QDs) stemming, respectively, from diminishing different polytypes (3C, 6H, and 4H) of bulk SiC crystals using electrochemical method. The three types of obtained SiC QDs show unexpected quite-similar photoluminescence, photoluminescence excitation, and transient photoluminescence properties. This strange phenomenon is explained by using the polytypic transformations of the colloidal SiC QDs driven by ultrasonic waves. Our results will greatly deepen our understanding of the fundamental physics of nanoscale SiC.
TL;DR: In this paper, a simple, physically consistent, and practical prescription for converting the luminescence spectra into absorption is presented and its relation to the so-called nonequilibrium generalization of the van Roosbroeck-Shockley relationship is discussed.
Abstract: The problem of conversion of experimentally measured luminescence spectrum into the absorption cross section is revisited. The common practice of using the van Roosbroeck-Shockley (or Kubo-Martin-Schwinger or Kennard-Stepanov) relation in this context is incorrect because luminescence from semiconductors is essentially all due to the spontaneous emission component of the recombination of carriers distributed far-from-equilibrium. A simple, physically consistent, and practical prescription for converting the luminescence spectra into absorption is presented and its relation to the so-called nonequilibrium generalization of the van Roosbroeck-Shockley relationship is discussed.
TL;DR: The photoluminescence excitation of Eu 3+ ions results from the radiative intra-configurational f-f transitions that happen between the 5 D J (J ǫ 0, 1Õ 3 ) exited states and the 7 F J ( J Ã 0,1Õ 4 ) ground states.
TL;DR: In this article, Nanocrystalline Ca2Gd8Si6O26 (CGS) phosphors were synthesized by solvothermal reaction method and the structural and morphological properties of the samples were evaluated by X-ray diffraction and scanning electron microscopy.
Abstract: Nanocrystalline Ca2Gd8Si6O26 (CGS): Sm3+ phosphors were synthesized by solvothermal reaction method. The structural and morphological properties of the samples were evaluated by X-ray diffraction and scanning electron microscopy. The photoluminescence excitation and emission spectra along with decay properties were investigated as a function of Sm3+ concentration. Under 405 nm excitation wavelength, the photoluminescence spectra showed three emission peaks at 565 nm (4G5/2 → 6H5/2) and at 650 nm (4G5/2 → 6H9/2), and with an intense orange emission at 600 nm (4G5/2 → 6H7/2). Based on the orange emission performance, the Sm3+ concentration was optimized to be at 2 mol%. The low voltage cathodoluminescence (CL) properties were also performed for 2 mol% Sm3+-doped CGS phosphors as a function of accelerating voltage (1–5 kV). From the CL spectra, the reddish-orange emission was observed. The calculated Commission International De I-Eclairage chromaticity coordinates are in close proximity to the chromaticity coordinates of Nichia corporation developed amber light emitting diodes.
TL;DR: In this paper, a MWO 4 :Sm 3+ (M = Ca, Sr and Ba) red phosphor with spherical microparticles was successfully prepared via a mild and facile hydrothermal route.
TL;DR: In this article, the donor-acceptor pair band excitation channels were determined by photoluminescence excitation spectroscopy in conjunction with temperature-dependent photoluminance measurements, which is put into a broader context based on Haynes's rule.
Abstract: Mg doping of high quality, metal organic chemical vapor deposition grown GaN films results in distinct traces in their photoluminescence and photoluminescence excitation spectra. We analyze GaN:Mg grown on sapphire substrates and identify two Mg related acceptor states, one additional acceptor state and three donor states that are involved in the donor-acceptor pair band transitions situated at 3.26–3.29 eV in GaN:Mg. The presented determination of the donor-acceptor pair band excitation channels by photoluminescence excitation spectroscopy in conjunction with temperature-dependent photoluminescence measurements results in a direct determination of the donor and acceptor binding, localization, and activation energies, which is put into a broader context based on Haynes’s rule. Furthermore, we analyze the biexponential decay dynamics of the photoluminescence signal of the acceptor and donor bound excitons. As all observed lifetimes scale with the localization energy of the donor and acceptor related bound excitons, defect and complex bound excitons can be excluded as their origin. Detailed analysis of the exciton transfer processes in the close energetic vicinity of the GaN band edge reveals excitation via free and bound excitonic channels but also via an excited state as resolved for the deepest localized Mg related acceptor bound exciton. For the two Mg acceptor states, we determine binding energies of 164 ± 5 and 195 ± 5 meV, which is in good agreement with recent density functional theory results. This observation confirms and quantifies the general dual nature of acceptor states in GaN based on the presented analysis of the photoluminescence and photoluminescence excitation spectra.
TL;DR: In this paper, a promising dual-mode solar spectral converter CaLaGa3S6O:Ce3+,Pr3+ for Si solar cells has been successfully developed, which can almost harvest UV-blue-red (250-625 nm) photons, greatly enhancing the utilization of solar spectrum especially in UV-Vis spectrum region, and convert into an intense broad NIR emission (930-1060 nm), perfectly matching the maximum spectral response of Si cells.
Abstract: A promising dual-mode solar spectral converter CaLaGa3S6O:Ce3+,Pr3+ for Si solar cells has been successfully developed. The structure, photoluminescence excitation and emission spectra in the UV-Vis-NIR region, and the decay curves have been systematically investigated. The results show that CaLaGa3S6O:Ce3+,Pr3+ exhibits two distinct solar spectral converting behaviors, quantum cutting (QC) (3PJ = 0,1,2 → 1G4 → 3H4) and downshift (DS) processes (1D2 → 3FJ = 3,4), depending on different excited levels of Pr3+ and Ce3+. It can almost harvest UV-blue-red (250–625 nm) photons, greatly enhancing the utilization of solar spectrum especially in UV-Vis spectrum region, and convert into an intense broad NIR emission (930–1060 nm), perfectly matching the maximum spectral response of Si solar cells. We demonstrate that Ce3+/Pr3+ ions can form an efficient donor–acceptor pair, with high potential as full spectrum solar converter for Si solar cells, and Ce3+ ion can be an efficient sensitizer for harvesting UV photon and greatly enhancing the NIR emission of Pr3+ ion through efficient energy feeding by allowed 4f–5d absorption of Ce3+ ion with high oscillator strength. The NIR integrated emission intensity of CaLaGa3S6O:Ce3+,Pr3+ is 7.78 times as intense as that of a NIR quantum cutting phosphor Ca2BO3Cl:Ce3+,Tb3+,Yb3+ (CBC). We believe this new dual-mode solar spectral converter may open a new route to the design of advanced UV-Vis–NIR phosphors for Si based solar cell applications.
TL;DR: In this paper, an efficient near-infrared quantum cutting downconversion from Yttrium lithium fluoride single crystals doped with trivalent lanthanide ions Pr3+ and Yb3+ was observed.
Abstract: Yttrium lithium fluoride single crystals doped with trivalent lanthanide ions Pr3+ and Yb3+ are prepared by an improved Bridgman method. X-ray diffraction, photoluminescence excitation, and emission spectra and decay curves are measured to investigate the structural and luminescent properties of the crystals. An efficient near-infrared quantum cutting downconversion from the crystals was observed. The downconversion involves the emission of two near-infrared photons for each blue photon absorbed at 480 nm via cross relaxation energy transfer from Pr3+ to Yb3+. Decay curve fitting using a modified Inokuti-Hirayama expression indicates dipole-dipole energy transfer from Pr3+ to Yb3+, which is consistent with the expected cross-relaxation scheme. The maximum quantum cutting efficiency approaches up to 168.4% in LiYF4: 0.28 mol. % Pr3+ and 6.02 mol. % Yb3+, and this is equivalent to 68.4% energy transfer efficiency.
TL;DR: In this article, the red-emitting nano-phosphors were characterized by X-ray powder diffraction, scanning electron microscope and photoluminescence excitation and emission measurements.
TL;DR: In this article, the temperature dependence of the photoluminescence (PL) and photoluminance excitation characteristics of the green emission band in undoped ZnO crystals was explored.
Abstract: We explore the temperature dependence of the photoluminescence (PL) and photoluminescence excitation characteristics of the green emission band in undoped ZnO crystals. We find that there exists a thermally assisted luminescence channel, which tends to dominate over the existing luminescence channel especially under below-band-gap excitation. Shallow donor electrons are likely to contribute to the thermally assisted luminescence process by being thermally excited from the donor levels to the conduction band. We hence suggest that the shallow donor centers, which are presumably attributed to zinc interstitials and will not act as emitting centers by themselves, are indirectly responsible for the green PL emission. The most probable candidate of the emitting center is the neutral oxygen vacancy, showing the green emission either via a direct internal emission process or an indirect thermally assisted emission process in combination with shallow donor centers.
TL;DR: In this paper, the exciton-LO-phonon progressions in the low temperature (4.2 K) photoluminescence excitation spectra of different types of colloidal NCs are reported.
Abstract: In this paper, the observation of LO-phonon progressions in the low temperature (4.2 K) photoluminescence excitation spectra of different types of colloidal NCs is reported. The strength of the exciton-LO-phonon coupling at 4.2 K, as reflected by the Huang–Rhys parameter S, increases from CdSe QDs (S = 0.8–1.0) to Type-I1/2 CdTe/CdSe HNCs (S = 1.5), and from these to Type-II CdTe/CdSe HNCs (S = 2.9). This trend is explained by the decrease in the electron–hole wave function overlap that accompanies the gradual increase in the CdSe volume fraction in the HNCs. The decrease in the electron–hole overlap increases the exciton polarization, which in turn enhances the exciton-LO-phonon coupling via the Frohlich interaction. The results provide novel insights into the nature of spatially indirect exciton transitions and show that compositional control of semiconductor heteronanocrystals can be used as a very effective tool to tailor the exciton–phonon coupling strength of nanoscale excitons.
TL;DR: It is revealed that the outstanding tube-structure preference of PFOPy can be interpreted by a characteristic "wavy" conformation ofPFOPy on the tube wall.
Abstract: For applications in standard optical devices, single-wall carbon nanotubes (SWCNTs) exhibiting emissions near 1500 nm are potentially feasible because silicon semiconductors efficiently transmit the light in this region. However, techniques to extract such semiconducting SWCNTs have not been reported thus far. In this study, using poly(9,9-dioctylfluorene-alt-pyridine) (PFOPy) as a dispersant in organic solvent, we succeeded in selectively dispersing SWCNTs which show near-infrared fluorescence around 1500 nm. On the basis of optical absorption and photoluminescence excitation spectroscopy, we revealed that the outstanding tube-structure preference of PFOPy can be interpreted by a characteristic “wavy” conformation of PFOPy on the tube wall.
TL;DR: In this article, a series of single-phased Ca2Al2SiO7:Eu2+ phosphors were synthesized by the solid-state reaction and their structure and photoluminescence properties were investigated by the X-ray powder diffraction (XRD) and excitation and emission spectra in detail.
TL;DR: In this article, vanadium-doped Zn2SiO4 particles embedded in a silica host matrix were prepared by a simple solid-phase reaction after the incorporation of ZnO and ZnV nanoparticles, respectively, in silica monolith using the sol-gel method with supercritical drying of ethyl alcohol.
TL;DR: In this article, the influence of different structures and bonding of the hosts on the luminescence performance of Eu3+ ion-doped trigonal LaAlO3 and GdAlO 3 was investigated in detail based on chemical bond theory.
TL;DR: In this paper, multicolor emission is reported from ultrasmall (<10 nm) β-NaYF4:Eu,Tb nanocrystals depending on the excitation wavelengths or emission detection delay time.
Abstract: Multicolor emission is reported from ultrasmall (<10 nm) β-NaYF4:Eu,Tb nanocrystals depending on the excitation wavelengths or emission detection delay time Detailed optical investigations of three samples (NaYF4:Eu, NaYF4:Tb and NaYF4:Eu,Tb) obtained by a co-thermolysis method have been carried out Photoluminescence, photoluminescence excitation and emission decay time obtained at different excitation wavelengths have been measured Excitation mechanisms of Eu and Tb ions have been explained based on the experimental results and calculations using Judd–Ofelt theory It has been shown that efficient energy transfer from Tb to Eu ions accounts for the efficient red emission of NaYF4:Tb,Eu nanocrystals
TL;DR: In this article, the photoluminescence of zinc oxide nanowires was investigated via the thermal annealing treatment in oxygen-rich and oxygen-poor conditions, and dramatic changes in the relative intensity of the ultraviolet and the green visible luminescence were observed following different annesaling treatments.
Abstract: The photoluminescence of zinc oxide nanowires was investigated via the thermal annealing treatment in oxygen-rich and oxygen-poor conditions. Dramatic changes in the relative intensity of the ultraviolet and the green visible luminescence were observed following different annealing treatments. The changes in photoluminescence bear little correlation to the changes in the oxygen-to-zinc ratios that were revealed using Raman scattering and other characterization techniques. The chemisorption of oxygen and the subsequent surface band bending, instead of the oxygen vacancy concentration, are shown to be the mechanism that determines the observed changes in photoluminescence.
TL;DR: The optical spectroscopy techniques were shown to be sufficient in determination of surface passivation of nanocrystals with high surface to volume ratio and significantly diminish for surface passivated nanocrystal.
Abstract: We examined in detail the optical properties of NaYF4:Eu3+ nanocrystals of ~9 nm in diameter. For such small nanocrystals roughly 17 % of Y3+ ions occupy surface sites and can be efficiently substituted by optically active Eu3+ ions. In order to determine the influence of surface Eu3+ on the optical properties of the whole nanocrystal, small β-NaYF4:Eu3+ nanocrystals with homogenous size distribution were prepared using trioctylphosphine oxide as a coordinating solvent. In order to passivate the surface sites, a thin β-NaYF4 shell was further deposited on nanocrystals core and the optical properties were investigated. For this purpose absorption, photoluminescence, photoluminescence excitation, and photoluminescence decays were recorded and analyzed. The optical characteristics of surface Eu3+ significantly diminish for surface passivated nanocrystals. We calculated the increase of quantum yield to the value of 64 % when NaYF4:Eu3+ core was capped by undoped shell. The optical spectroscopy techniques were shown to be sufficient in determination of surface passivation of nanocrystals with high surface to volume ratio.
TL;DR: In this article, Eu2+-activated K4CaSi3O9 phosphors were synthesized by conventional solid-state reaction and the phase formation was confirmed by X-ray powder diffraction measurements.
TL;DR: In this paper, the preparation of pure or doped lutetium aluminium garnet Lu3Al5O12 (LuAG) is reported as a simple and robust process, which is easy to control.
Abstract: Radiation-induced preparation of pure or doped lutetium aluminium garnet Lu3Al5O12 (LuAG) is reported as a simple and robust process, which is easy to control. Irradiation of an aqueous solution containing formate anions and soluble salts of both metal ions by ionizing radiation or UV light leads to precipitation of an amorphous solid phase. Subsequent calcination in the interval 850–1200 °C results in the crystallization of the LuAG with a well developed structure. Depending on the calcination temperature, the particle size ranges from 20 to 60 nm; the prepared LuAG nanopowder was also found to be easily compactable. The manufactured Ce-doped LuAG features intensive luminescence corresponding to Ce3+ 5d–4f transitions at 510 nm and its photoluminescence excitation spectrum comprises two Ce3+ 4f–5d1, 5d2 bands at 450 and 347 nm, respectively. The decay times of Ce3+ emission in nanopowders were substantially influenced by the nanomorphological character of the prepared material. Due to its high density, chemical stability, non-toxic character and excellent scintillation efficiency, the application of Ce-doped LuAG nanopowder in photodynamic therapy and in optical ceramics preparation is suggested.