Showing papers on "Photoluminescence published in 2006"
TL;DR: It is reported that nanoscale carbon particles (carbon dots) upon simple surface passivation are strongly photoluminescent in both solution and the solid state.
Abstract: We report that nanoscale carbon particles (carbon dots) upon simple surface passivation are strongly photoluminescent in both solution and the solid state. The luminescence emission of the carbon dots is stable against photobleaching, and there is no blinking effect. These strongly emissive carbon dots may find applications similar to or beyond those of their widely pursued silicon counterparts.
3,817 citations
TL;DR: A review of current research on the optical properties of ZnO nanostructures and results of nonlinear optical studies, such as second-harmonic generation, are presented.
Abstract: We present a review of current research on the optical properties of ZnO nanostructures. We provide a brief introduction to different fabrication methods for various ZnO nanostructures and some general guidelines on how fabrication parameters (temperature, vapor-phase versus solution-phase deposition, etc.) affect their properties. A detailed discussion of photoluminescence, both in the UV region and in the visible spectral range, is provided. In addition, different gain (excitonic versus electron hole plasma) and feedback (random lasing versus individual nanostructures functioning as Fabry-Perot resonators) mechanisms for achieving stimulated emission are described. The factors affecting the achievement of stimulated emission are discussed, and the results of time-resolved studies of stimulated emission are summarized. Then, results of nonlinear optical studies, such as second-harmonic generation, are presented. Optical properties of doped ZnO nanostructures are also discussed, along with a concluding outlook for research into the optical properties of ZnO.
1,746 citations
TL;DR: In this article, the photoluminescence (PL) performance and mechanism of nano-sized semiconductor materials, such as TiO 2 and ZnO, are introduced, together with their attributes and affecting factors.
1,578 citations
TL;DR: Photoluminescent measurements indicate that the value of I610/I590 and the overall emission intensity of the NaEuF4 nanocrystals are highly correlative with the symmetries of the Eu3+ ions in both the lattice and the surface.
Abstract: We report a general synthesis of high-quality cubic (α-phase) and hexagonal (β-phase) NaREF4 (RE: Pr to Lu, Y) nanocrystals (nanopolyhedra, nanorods, nanoplates, and nanospheres) and NaYF4:Yb,Er/Tm nanocrystals (nanopolyhedra and nanoplates) via the co-thermolysis of Na(CF3COO) and RE(CF3COO)3 in oleic acid/oleylamine/1-octadecene. By tuning the ratio of Na/RE, solvent composition, reaction temperature and time, we can manipulate phase, shape, and size of the nanocrystals. On the basis of its α → β phase transition behavior, along the rare-earth series, NaREF4 can be divided into three groups (I: Pr and Nd; II: Sm to Tb; III: Dy to Lu, Y). The whole controlled-synthesis mechanism can be explained from the point of view of free energy. Photoluminescent measurements indicate that the value of I610/I590 and the overall emission intensity of the NaEuF4 nanocrystals are highly correlative with the symmetries of the Eu3+ ions in both the lattice and the surface.
1,338 citations
TL;DR: ZnO nanorod arrays were fabricated using a hydrothermal method and found that, while the defect emission can be significantly reduced by annealing at 200 degrees C, the rods still have large defect concentrations as confirmed by their low positron diffusion length and short PL decay time constants.
Abstract: ZnO nanorod arrays were fabricated using a hydrothermal method. The nanorods were studied by scanning electron microscopy, photoluminescence (PL), time-resolved PL, X-ray photoelectron spectroscopy, and positron annihilation spectroscopy before and after annealing in different environments and at different temperatures. Annealing atmosphere and temperature had significant effects on the PL spectrum, while in all cases the positron diffusion length and PL decay times were increased. We found that, while the defect emission can be significantly reduced by annealing at 200 °C, the rods still have large defect concentrations as confirmed by their low positron diffusion length and short PL decay time constants.
722 citations
TL;DR: The first known observation of efficient multiple exciton generation (MEG) from single photons absorbed in PbTe NCs is reported, and calculated longitudinal and transverse Bohr radii for PbS, PbSe, and Pb Te NCs are reported to account for electronic band anisotropy.
Abstract: We report an alternative synthesis and the first optical characterization of colloidal PbTe nanocrystals (NCs). We have synthesized spherical PbTe NCs having a size distribution as low as 7%, ranging in diameter from 2.6 to 8.3 nm, with first exciton transitions tuned from 1009 to 2054 nm. The syntheses of colloidal cubic-like PbSe and PbTe NCs using a PbO "one-pot" approach are also reported. The photoluminescence quantum yield of PbTe spherical NCs was measured to be as high as 52 +/- 2%. We also report the first known observation of efficient multiple exciton generation (MEG) from single photons absorbed in PbTe NCs. Finally, we report calculated longitudinal and transverse Bohr radii for PbS, PbSe, and PbTe NCs to account for electronic band anisotropy. This is followed by a comparison of the differences in the electronic band structure and optical properties of these lead salts.
674 citations
TL;DR: In this paper, the spatial variation of the effective minority carrier lifetime is measured without being affected by minority carrier trapping or by excess carriers in space charge regions, effects that lead to experimental artifacts in other techniques.
Abstract: Photoluminescence imaging is demonstrated to be an extremely fast spatially resolved characterization technique for large silicon wafers. The spatial variation of the effective minority carrier lifetime is measured without being affected by minority carrier trapping or by excess carriers in space charge regions, effects that lead to experimental artifacts in other techniques. Photoluminescence imaging is contactless and can therefore be used for process monitoring before and after individual processing stages, for example, in photovoltaics research. Photoluminescence imaging is also demonstrated to be fast enough to be used as an in-line tool for spatially resolved characterization in an industrial environment.
651 citations
TL;DR: In this article, the gallium-doped n-type ZnO with a thickness of 1.5 lm was grown on a c-Al2O3 substrate and showed excellent current-rectifying behavior with a threshold voltage of 3.2 V and an EL emission peak at 380 nm at room temperature.
Abstract: to improve the structural properties of n- and p-type ZnO compared to previous studies. [7] In addition, a thermal annealing process was carried out to activate the phosphorus dopants in p-type ZnO and improve the electrical and optical properties of the ZnO layers. The LED showed excellent current-rectifying behavior with a threshold voltage of 3.2 V and an EL emission peak at 380 nm at room temperature. The UV EL emission spectrum was in good agreement with the room-temperature photoluminescence (PL) spectrum of the p-type ZnO used in the LED. Furthermore, the near-bandedge emission was increased and the deep-level emission was decreased when (Mg,Zn)O alloy layers were introduced as energy barrier layers between n-type and p-type ZnO films to confine the carrier recombination process to the high-quality n-type ZnO film. A schematic diagram of the p–n homojunction ZnO LED is shown in Figure 1. The gallium-doped n-type ZnO with a thickness of 1.5 lm was grown on a c-Al2O3 substrate. It
624 citations
TL;DR: It was found that use of a pulsed MOCVD process allowed thenanowire diameter to remain constant after the nanowires had emerged from the selective growth mask, while remarkably the diameter of each nanowire remained constant over the entire (micrometer) length of the Nanowires.
Abstract: This paper reports a scalable process for the growth of high-quality GaN nanowires and uniform nanowire arrays in which the position and diameter of each nanowire is precisely controlled. The approach is based on conventional metalorganic chemical vapor deposition using regular precursors and requires no additional metal catalyst. The location, orientation, and diameter of each GaN nanowire are controlled using a thin, selective growth mask that is patterned by interferometric lithography. It was found that use of a pulsed MOCVD process allowed the nanowire diameter to remain constant after the nanowires had emerged from the selective growth mask. Vertical GaN nanowire growth rates in excess of 2 μm/h were measured, while remarkably the diameter of each nanowire remained constant over the entire (micrometer) length of the nanowires. The paper reports transmission electron microscopy and photoluminescence data.
597 citations
TL;DR: In this article, a spectroscopic investigation of NaYF4 powders doped with several different concentrations of Er 3 +, Tm 3 + and/or Yb 3 + is described.
543 citations
TL;DR: In this article, photoluminescence from ZnO nanostructures prepared by different methods (needles, rods, shells) was measured as a function of excitation wavelength and temperature.
Abstract: ZnO commonly exhibits luminescence in the visible spectral range due to different intrinsic defects. In order to study defect emissions, photoluminescence from ZnO nanostructures prepared by different methods (needles, rods, shells) was measured as a function of excitation wavelength and temperature. Under excitation at 325nm, needles exhibited orange-red defect emission, rods exhibited yellow defect emission, while shells exhibited green defect emission. Obvious color change from orange to green was observed for needles with increasing excitation wavelengths, while nanorods (yellow) showed smaller wavelength shift and shells (green) showed no significant spectral shift. Reasons for different wavelength dependences are discussed.
TL;DR: It is proposed that surface Cd vacancies function as nonradiative recombination centers and the adsorption of a Lewis base to the QD raises the surface vacancy energy close to, or above, the conduction band edge and eliminates electron capture by the surface vacancies.
Abstract: We report on the effects of Lewis bases and other ligands on radiative recombination in CdSe quantum dots (QDs) in several solvents. Long-chain primary amines are found to be the most efficacious capping agents for CdSe QDs in nonpolar solvents. Primary alkylamines are superior to secondary and tertiary alkylamines. The kinetics of chemisorption and desorption in less polar solvents, such as hexane or chloroform, are temperature controlled and obey a Langmuir isotherm. Mercaptan adsorption also obeys a Langmuir isotherm, and alkylmercaptans rapidly displace amines, leading to luminescence quenching. In more polar solvents, such as toluene, ligands desorb, leading to luminescence quenching. It is proposed that surface Cd vacancies function as nonradiative recombination centers. The adsorption of a Lewis base to the QD raises the surface vacancy energy close to, or above, the conduction band edge and eliminates electron capture by the surface vacancies. Solvent polarity has a strong effect on luminescence since the solvent determines the extent of ligand adsorption to the QD surface.
TL;DR: In agreement with the model of Persson and Lang, all experimental data show that energy transfer to the metal surface is the dominant quenching mechanism, and the radiative rate is unchanged throughout the experiment.
Abstract: The fluorescence behavior of molecular dyes at discrete distances from 15 nm diameter gold nanoparticles as a function of distance and energy is investigated Photoluminescence and luminescence lifetime measurements both demonstrate quenching behavior consistent with 1/d(4) separation distance from dye to the surface of the nanoparticle In agreement with the model of Persson and Lang, all experimental data show that energy transfer to the metal surface is the dominant quenching mechanism, and the radiative rate is unchanged throughout the experiment
TL;DR: In this paper, the emission peak position of (Sr1−xEux)2Si5N8:Eu2+ series varied from 618to690nm with increasing Eu2− ion concentration.
Abstract: Eu2+-doped ternary nitride phosphor, Sr2Si5N8:Eu2+, was prepared by the carbothermal reduction and nitridation method. The Rietveld refinement analysis showed that the single phase products were obtained. Two main absorption bands were observed on the diffuse reflection spectra peaking at about 330 and 420nm, so that the resultant phosphor can be effectively excited by InGaN light-emitting diodes. The emission peak position of (Sr1−xEux)2Si5N8:Eu2+ series varied from 618to690nm with increasing Eu2+ ion concentration. The redshift behavior of the emission band was discussed on the basis of the configuration coordination model.
TL;DR: In this paper, the authors reported the plasma synthesis of silicon quantum dots and their subsequent wet-chemical surface passivation with organic ligands under strict exclusion of oxygen, achieving photoluminescence quantum yields exceeding 60% at peak wavelengths of about 789nm.
Abstract: Silicon nanocrystals with diameters of less than 5nm show efficient photoluminescence at room temperature. For ensembles of silicon quantum dots, previous reports of photoluminescence quantum yields have usually been in the few percent range, and generally less than 30%. Here we report the plasma synthesis of silicon quantum dots and their subsequent wet-chemical surface passivation with organic ligands under strict exclusion of oxygen. Photoluminescence quantum yields exceeding 60% have been achieved at peak wavelengths of about 789nm.
TL;DR: In this article, large-area films of porous elastomeric photonic crystals (EPCs) are cycled to reversibly shift the position of the photonic band structure over a large wavelength range.
Abstract: In photonic crystals (PCs), strong scattering and destructive wave interference lead to a modification of the photon density of states in particular energy regions and along certain crystallographic directions1,2. The consequences of this range from suppression and enhancement of luminescence3,4,5,6,7 to narrow-band bright reflections useful for colour sensors8,9, displays10 and tuneable filters11,12,13,14. Here we demonstrate large-area films of porous elastomeric photonic crystals (EPCs) that are compressively–decompressively cycled to reversibly shift the position of the photonic band structure over a large wavelength range. Owing to their low compressive threshold, such porous EPCs can be used for imaging that is pressure and time sensitive, for example, to obtain colour fingerprints with high accuracy. Furthermore, by incorporating luminescent PbS quantum dots in the EPCs, the photonic stop-gap can be tuned through the near-infrared (NIR) quantum dot photoluminescence (PL) peak. Thereby we demonstrate a tuneable modification of photonic characteristics, including the suppression and enhancement in emission and dynamic modification of luminescence lifetimes.
TL;DR: In this paper, the authors studied the possible correlations between defects and photoluminescence spectra in ZnO nanoparticles of sizes ranging from 43 nm to 73 nm in diameter.
Abstract: We studied the possible correlations between defects and photoluminescence spectra in ZnO nanoparticles of sizes ranging from 43 nm to 73 nm in diameter. The defects and impurity contents were characterized by Fourier-transform infrared (FTIR) spectroscopy. The results show fewer carboxylate and hydroxyl impurities for particles of larger sizes. No significant variation in oxygen vacancy content was found among samples. Annealing in vacuum at 300 °C significantly reduces the carboxylate and hydroxyl impurities in the samples. The total luminescence intensity (UV + visible) increases as the particle size grows for both the unannealed and annealed samples. This suggests that both types of luminescence are subject to non-radiative quenching by near surface defect centers, possibly carboxylate and hydroxyl impurities. There may be quenching due to intrinsic lattice defects too. It is found that annealing in vacuum enhances the visible luminescence both absolutely and relative to the UV exciton luminescence. In addition to the 2.5 eV green luminescence peak, a peak centered at 2.8 eV can also be resolved, espeically for the 43 nm sample. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: It can be suggested that the SOVs should play an important role during the processes of PL, surface photovoltage, and photocatalytic reactions, and, for the as-prepared TiO(2) samples doped with different amounts of Zn by thermal treatment at 550 degrees C, the larger the Sov amount, the stronger the PL and SPS signal, and the higher the photoc atalytic activity.
Abstract: In this paper, TiO2 nanoparticles doped with different amounts of Zn were prepared by a sol−gel method and were mainly characterized by means of X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), and surface photovoltage spectrum (SPS). The effects of surface oxygen vacancies (SOVs) of Zn-doped TiO2 nanoparticles on photophysical and photocatalytic processes were investigated along with their inherent relationships. The results show that the SOVs easily bind photoinduced electrons to further give rise to PL signals. The SOVs can result in an interesting sub-band SPS response near the band edge in the TiO2 sample consisting of much anatase and little rutile, except for an obvious band-to-band SPS response. Moreover, the intensities of PL and SPS signals of TiO2, as well as the photocatalytic activity for degrading phenol solution, can be enhanced by doping an appropriate amount of Zn. These improvements are mainly attributed to the increase in the SOV amount. It can be suggested that the SOVs ...
TL;DR: In this paper, the authors used photoluminescence spectroscopy to study single crystalline ZnO samples systematically annealed in inert, Zn-rich and O-rich atmospheres.
Abstract: Photoluminescence spectroscopy has been used to study single crystalline ZnO samples systematically annealed in inert, Zn-rich and O-rich atmospheres. A striking correlation is observed between the choice of annealing ambient and the position of the deep band emission (DBE) often detected in ZnO. In particular, annealing in O2 results in a DBE at 2.35±0.05eV, whereas annealing in the presence of metallic Zn results in DBE at 2.53±0.05eV. The authors attribute the former band to zinc vacancy (VZn) related defects and the latter to oxygen vacancy (VO) related defects. Additional confirmation for the VO and VZn peak identification comes from the observation that the effect is reversible when O- and Zn-rich annealing conditions are switched. After annealing in the presence of ZnO powder, there is no indication for the VZn- or VO-related bands, but the authors observe a low intensity yellow luminescence band peaking at 2.17eV, probably related to Li, a common impurity in hydrothermally grown ZnO.
TL;DR: The photoluminescence of both kinds of particles (anatase and rutile) with several well-resolved peaks extending in the visible spectral region was observed, and the quantum yield at room temperature was found to be 0.25%.
Abstract: Nonaqueous reactions between titanium(IV) chloride and alcohols (benzyl alcohol or n-butanol) were used for the synthesis of anatase TiO2 particles, while rutile TiO2 particles were synthesized in aqueous media by acidic hydrolysis of titanium(IV) chloride. The X-ray diffraction measurements proved the exclusive presence of either the anatase or the rutile phase in prepared samples. The photoluminescence of both kinds of particles (anatase and rutile) with several well-resolved peaks extending in the visible spectral region was observed, and the quantum yield at room temperature was found to be 0.25%. Photon energy up-conversion from colloidal anatase and rutile TiO2 particles was observed at low excitation intensities. The energy of up-converted photoluminescence spans the range of emission of normal photoluminescence. The explanation of photon energy up-conversion involves mid-gap energy levels originating from oxygen vacancies.
TL;DR: The shape-controlled synthesis of ZnIn2S4, CuInS2, and CuInSe2 nano- and microstructures through a facile solution-based route is demonstrated and the UV-vis absorption spectra show that the as-prepared Nano- and micromaterials have strong absorption in a wide range from UV to visible light and their band gaps are somewhat relevant to the size and morphology.
Abstract: We demonstrated in this paper the shape-controlled synthesis of ZnIn2S4, CuInS2, and CuInSe2 nano- and microstructures through a facile solution-based route. One-dimensional ZnIn2S4 nanotubes and nanoribbons were synthesized by a solvothermal method with pyridine as the solvent, while ZnIn2S4 solid or hollow microspheres were hydrothermally prepared in the presence of a surfactant such as cetyltrimethylammonium bromide (CTAB) or poly(ethylene glycol) (PEG). The mechanisms related to the phase formation and morphology control of ZnIn2S4 are proposed and discussed. The UV−vis absorption spectra show that the as-prepared nano- and micromaterials have strong absorption in a wide range from UV to visible light and that their band gaps are somewhat relevant to the size and morphology. The photoluminescence measurements of the ZnIn2S4 microspheres at room temperature reveal intense excitation at ∼575 nm and red emission at ∼784 nm. Furthermore, CuInS2 and CuInSe2 with different morphologies such as spheres, plat...
TL;DR: In this article, the effects of annealing temperature and dopant concentration on the structural and optical properties of ZnO:Al, AZO thin films have been discussed and the minimum sheet resistance of 10 4 ǫ/□ was obtained for the film doped with 1.6% Al, annealed at 750°C.
TL;DR: In this article, the room-temperature photoluminescence (PL) of copper doped zinc sulfide (ZnS:Cu) nanoparticles was investigated, with the copper concentration varying from 0 to 2 mol%.
TL;DR: Several conjugated thieno[3,4b]pyrazine-based donor-acceptor copolymers were synthesized by Stille and Suzuki copolymerizations, and their optical, electrochemical, and field-effect charge transport properties were characterized.
Abstract: Several conjugated thieno[3,4-b]pyrazine-based donor−acceptor copolymers were synthesized by Stille and Suzuki copolymerizations, and their optical, electrochemical, and field-effect charge transport properties were characterized. The new copolymers, poly(5,7-bis(3-dodecylthiophen-2-yl)thieno[3,4-b]pyrazine) (BTTP), poly(5,7-bis(3-dodecylthiophen-2-yl)thieno[3,4-b]pyrazine-alt-2,5-thiophene) (BTTP-T), poly(5,7-bis(3-dodecylthiophen-2-yl)thieno[3,4-b]pyrazine-alt-9,9-dioctyl-2,7-fluorene) (BTTP-F), and poly(5,7-bis(3-dodecylthiophen-2-yl)thieno[3,4-b]pyrazine-alt-1,4-bis(decyloxy)phenylene) (BTTP-P), had moderate to high molecular weights, broad optical absorption bands that extend into the near-infrared region with absorption maxima at 667−810 nm, and small optical band gaps (1.1−1.6 eV). They showed ambipolar redox properties with low ionization potentials (HOMO levels) of 4.6−5.04 eV. The field-effect mobility of holes varied from 4.2 × 10-4 cm2/(V s) in BTTP-T to 1.6 × 10-3 cm2/(V s) in BTTP-F. These r...
TL;DR: In this article, the authors investigated solid-state self-quenching processes of highly efficient Ir(III) phosphorescent emitters by measuring thin film photoluminescence quantum efficiency and transient lifetime as a function of doping concentration in host matrix.
Abstract: Solid-state self-quenching processes of highly efficient Ir(III) phosphorescent emitters are investigated by the measurement of thin film photoluminescence quantum efficiency and transient lifetime as a function of doping concentration in a host matrix. The radiative decay rate constant is found to be independent from the average distance between dopant molecules (R), and the concentration-quenching rate constant is shown to be dependent on R(-6). The quenching dependence on R strongly suggests that luminescent concentration quenching in a phosphorescent Ir(III) complex:host film is controlled by dipole-dipole deactivating interactions as described by the Forster energy transfer model.
TL;DR: A new family of homoleptic iridium(III) complexes that emit blue phosphorescence at room temperature was reported in this article, consisting of phenyltriazole ligands and were easily prepared via short synthetic routes.
Abstract: We report a new family of homoleptic iridium(III) complexes that emit blue phosphorescence at room temperature. The iridium( III) complexes are comprised of phenyltriazole ligands and were easily prepared via short synthetic routes. The parent fac-tris(1-methyl-5-phenyl-3-propyl-[1,2,4]triazolyl)iridium(III) complex exhibits blue photoluminescence (PL) with emission peaks at 449 and 479 nm and has a solution PL quantum yield of 66%. The emission was sequentially blue-shifted by the attachment of one and two fluorine atoms to the ligand phenyl ring with the fac-tris{1-methyl-5-(4,6-difluorophenyl)-3-propyl-[1,2,4]triazolyl} iridium( III) complex having the 1931 Commission Internationale de l'Eclairage coordinates of (0.16, 0.12) at room temperature. In contrast, when the phenyl ring of the ligands was substituted by trifluoromethyl, the PL spectrum was red-shifted when compared to the parent compound whereas if the trifluoromethyl group was attached to the triazole ring, the emission was blue-shifted. The radiative rates of these new blue iridium( III) complexes were found to be in the range of 2-6 x 105 s(-1), indicating that the emission had varying amounts of metal-to-ligand charge-transfer character. Molecular orbital calculations showed that for the fluorinated complexes the contribution of the ligand triplet character to the emissive energy state increased with the hypsochromic shift in emission. This was confirmed by time-resolved PL measurements, which showed that the complex with the deepest blue emission had the slowest radiative decay rate.
TL;DR: In this paper, the fabrication methods as well as optical and electrical characteristics of silicon carbide nanocrystals, nanowires, nanotubes, and nanosized films are reviewed.
TL;DR: CeF3, CeF3:Tb3+ and Tb3/LaF3 (core/shell) nanoparticles were obtained by the polyol method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-Ray photoelectron spectra (XPS), UV−vis absorption spectra, photoluminescence (PL) spectra and lifetimes as mentioned in this paper.
Abstract: CeF3, CeF3:Tb3+, and CeF3:Tb3+/LaF3 (core/shell) nanoparticles were prepared by the polyol method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), UV−vis absorption spectra, photoluminescence (PL) spectra, and lifetimes. The results of XRD indicate that the obtained CeF3, CeF3:Tb3+, and CeF3:Tb3+/LaF3 (core/shell) nanoparticles crystallized well at 200 °C in diethylene glycol (DEG) with a hexagonal structure. The TEM images illustrate that the CeF3 and CeF3:Tb3+ nanoparticles are spherical with a mean diameter of 7 nm. The growth of the LaF3 shell around the CeF3:Tb3+ core nanoparticles resulted in an increase of the average size (11 nm) of the nanopaticles as well as in a broadening of their size distribution. These nanocrystals can be well-dispersed in ethanol to form clear colloidal solutions. The colloidal solutions of CeF3 and CeF3:Tb3+ show the characteristic emission of Ce3+ 5d−4f (320 nm) and Tb3+ 5D4−7FJ (J = 6−3, with 5D4−7F...
TL;DR: In this article, the authors investigated the temperature-dependent photoluminescence decay of efficiently luminescing organically capped CdSe quantum dots with diameters ranging from 1.7 to 6.3 nm over a broad temperature range 1.3-300 K.
Abstract: In this work we have investigated the temperature-dependence of the band-edge photoluminescence decay of efficiently luminescing organically capped CdSe quantum dots QDs with diameters ranging from 1.7 to 6.3 nm over a broad temperature range 1.3– 300 K. The overall trend is similar for all the investigated sizes, consisting of different temperature regimes. The low-temperature regime below 50 K is characterized by purely radiative decay and can be modeled by a thermal distribution between a lower dark and a higher bright exciton state, with a size-dependent energy separation viz., from 0.7 to 1.7 meV and dark exciton lifetime viz., from 0.3 to 1.4 s for QDs ranging from 6.3 nm to 1.7 nm in diameter. Nonradiative relaxation processes become increasingly important above 50 K until the temperature antiquenching regime is reached, leading to a decrease in the nonradiative contributions and photoluminescence intensity recovery above 200 K.