Strong Light Emission Research Articles

Hydrothermal Synthesis and Luminescent Properties of Spherical LaPO<sub>4</sub>:Ln<sup>3+</sup> (Ln<sup>3+</sup>= Eu<sup>3+</sup>, Dy<sup>3+</sup>, Ce<sup>3+</sup>, Tb<sup>3+</sup>)

Uniform LaPO4 and LaPO4:Ln3+ (Ln3+= Eu3+, Dy3+, Ce3+, Tb3+) microspheres have been selectively synthesized via a hydrothermal route, without using any catalyst, or template. X-ray diffraction, SEM, TEM, and photoluminescence spectroscopy were used to characterize the phase structure, morphology, and luminescence properties of the as-prepared samples. SEM results indicate that as-obtained samples have perfect spherical morphology with narrow size distribution. PL excitation and emission spectra demonstrated the LaPO4:Ln3+ phosphors show strong light emissions with different colors coming from different activator ions under ultraviolet excitation, which might find potential applications in fields such as light phosphor powders and advanced flat panel displays.

Synthesis and optical properties of σ–π conjugated aluminum-containing polyphenylcarbosilane (Al-PPCS) by hydrosilylation polymerization

Optical properties of aryl-substituted polyphenylcarbosilane (PPCS) and aluminum-containing polyphenylcarbosilane (Al-PPCS) prepared by hydrosilylation polymerization were studied. Polycarbosilane (PCS), aluminum-containing polycarbosilane (Al-PCS) and styrene were employed as reactants to yield σ–π conjugated PPCS and Al-PPCS using chloroplatinic acid as catalyst, respectively. Phenyl was directly attached to the conjugated main chains with SiC bonds. Effects of divinyl benzene cross-linking, oxidation curing and ultraviolet (UV) radiation on the photoluminescence (PL) properties of the samples were examined. PL spectra show strong blue light emission and the intensity of PCS is enhanced by adding the aryl groups and Al atoms. The excellent luminescent properties are attributed to the delocalization of electrons from the σ bond to π system. The hyperbranched Al-PPCS with extended σ–π conjugation has an obvious red-shifts PL, high quantum yield, excellent oxidation resistance and good UV resistance performance. Thermal analysis reveals that Al-PPCS can keep structure stability below 400°C under an inert gas atmosphere. The Al-PPCS may have potential applications including organic electroluminescent (EL) devices.

Growth of semiconductor alloy InGaPBi on InP by molecular beam epitaxy

We report the first successful growth of InGaPBi single crystals on InP substrate with Bi concentration far beyond the doping level by gas source molecular beam epitaxy. The InGaPBi thin films reveal excellent surface and structural qualities, making it a promising new III–V compound family member for heterostructures. The strain can be tuned between tensile and compressive by adjusting Ga and Bi compositions. The maximum achieved Bi concentration is 2.2 ± 0.4% confirmed by Rutherford backscattering spectroscopy. Room temperature photoluminescence shows strong and broad light emission at energy levels much smaller than the InP bandgap.

Strong visible electroluminescence from silicon nanocrystals embedded in a silicon carbide film

We report the strong visible light emission from silicon (Si) nanocrystals (NCs) embedded in a Si carbide (SiC) film. Compared to Si NC light-emitting diode (LED) by employing the Si nitride (SiNx) film as a surrounding matrix, the turn-on voltage of the Si NC LED with the SiC film was significantly decreased by 4 V. This was attributed to a smaller barrier height for injecting the electrons into the Si NCs due to a smaller band gap of SiC film than a SiNx film. The electroluminescence spectra increases with increasing forward voltage, indicating that the electrons are efficiently injected into the Si NCs in the SiC film. The light output power shows a linear increase with increasing forward voltage. The light emission originated from the Si NCs in a SiC film was quite uniform. The power efficiency of the Si NC LED with the SiC film was 1.56 times larger than that of the Si NC LED with the SiNx film. The Si NCs in a SiC film show unique advantages and are a promising candidate for application in optical devices.

Localizable and photoactivatable fluorophore for spatiotemporal two-photon bioimaging.

Photoactivatable probe-based fluorescent imaging has become an efficient and attractive technique for spatiotemporal microscopic studies of biological events. However, almost all previously reported photoactivatable organic probes have been based on hydrosoluble precursors, which have produced water-soluble active fluorophores able to readily diffuse away from the photocleavage site, thereby dramatically reducing spatial resolution. Hydroxyphenylquinazolinone (HPQ), a small organic dye known for its classic luminescence mechanism through excited-state intramolecular proton transfer (ESIPT), shows strong light emission in the solid state, but no emission in solution. In this work, HPQ was employed as a precursor to develop a localizable, photoactivatable two-photon probe (PHPQ) for spatiotemporal bioimaging applications. After photocleavage, PHPQ releases a precipitating HPQ fluorophore which shows both one-photon and two-photon excited yellow-green fluorescence, thereby producing a localizable fluorescence signal that affords high spatial resolution for bioimaging, with more than 200-fold one-photon and 150-fold two-photon fluorescence enhancement.

Rating analysis and comparisons of resonant circuit based sustain drivers for PDPs

Industrial and academic researches have, in the last twenty years, matured the plasma display panels (PDPs) to the successful product level for commercial flat screen television sets. The sustain driver with resonant operation, converting high dc voltage to ac square-wave voltage with high frequency for strong visible light emission, have great influence on the entire circuit efficiency and cost, from driving circuit point. Although circuit losses and costs of PDP drivers are of the utmost importance, comparative study of the sustain drivers has been missed in literature, despite numerous publications for PDP drivers. This paper, in detail, presents the theoretical analyses and systematic comparisons of the PDP drivers, in terms of switch current and voltage ratings. Based on analytical expressions and comparative features, the sustain drivers are evaluated from standpoint of switch ratings.

Photoluminescent properties of oxidized stochiometric and carbon-rich amorphous Si1-xCx:H films

Near-stochiometric and carbon-rich a-Si1−xCx:H thin films were deposited using the magnetron sputtering of Si target in Ar/CH4 gas mixture. As-deposited nearstochimetric (x = 0.5) sample showed weak blue photoluminescence (PL), while PL of as-deposited carbon-rich (x = 0.7) sample was 20 times stronger and white in color. The films were annealed in pure argon, wet argon, and dry oxygen at 450 °C for 30 min. The intensity of PL in a-Si1−xCx:H layers were enhanced by the factor from 2 to 12 after annealing in dependence on the annealing atmosphere. The strongest oxidation and strongest light emission were observed in carbon-rich series (x = 0.7) after annealing in oxidizing atmosphere. Structural properties of the films were characterized by infra-red absorption spectroscopy, ellipsometry and electron paramagnetic resonance. The effect of carbon enrichment of a-Si1−xCx:H films and annealing atmosphere on the evolution of photoluminescence and local interatomic bonding structure in annealed material were studied and analyzed. It has been found that main effects of thermal treatments is strong enhancement of photoluminescence accompanied by formation of Si:C–Hn and Si–OxCy bonding. The strongest oxidation effect as well as strongest photoluminescence were observed in carbon-rich a-SiC:H films.

Development of vertically aligned ZnO-nanowires scintillators for high spatial resolution x-ray imaging

Newly designed scintillator of (0001)-oriented ZnO vertical nanowires (vnws) for X-ray imaging was prepared on a Ga-doped ZnO/soda-lime glass by electrodeposition, and the light emission feature was estimated in a synchrotron radiation facility. The ZnO-vnws scintillator revealed a strong light emission and improved resolution on CMOS image compared with that for the ZnO-layer scintillator, although the light emission performance was deteriorated in comparison to the Lu3Al5O12:Ce3+. The light emission property closely related to the nanostructure and the resultant photoluminescence characteristic.

Novel rib-like ZnxCd1−xS whiskers in silica matrix

ZnxCd1−xS whiskers in silica matrix with novel rib-like structure have been synthesized in high yield by a solid–vapor decomposition route. The whiskers are composed of ZnxCd1−xS rod-arrays grown closely parallel to each other with uniform diameter and length. The photoluminescence spectrum of the whiskers revealed a strong blue light emission peak at 469nm and a weak one at 533nm, suggesting their potential applications in short wavelength optoelectronic nanodevices.

Photoluminescence properties of Eu doped Si nanowires

High-density (～1010 cm-2) silicon nanowires are grown directly from n-(111) single crystal silicon based on solid-liquid-solid mechanism by using Au-Al films as metallic catalyst. The results indicate that the optimal parameters to realize Si nanowires with high density and uniform distribution are as follows. The thickness of Au-Al film is between 5 and 15 nm, the temperature is 1100℃, and the flow of N2 is 1.5 L/min. The diameters and lengths of the formed Si nanowires are 100 nm and from several micrometers to sereral tens of micrometerss, respectively. Then Eu-doped Si nanowires are studied. The influences of the different lengths of Si nanowires, doping temperature (900-1100℃), and doping time (15-60 min) on the luminescence of Eu3 + are experimentally investigated. The morphologies and microstructures of the SiNWs, the photoluminescence properties and growth crystall orientations are characterized and analyzed by the scanning electron microscopy, the Hitachi F-4600 fluorescence spectrophotometer and X-ray powder diffraction. The results show that the Eu-doped Si nanowires have a stronly red luminescencent with an emission peak position at 619 nm (5D0→7F2) when the doping temperature is 1000℃, the grow time of SiNWs is 30 min, and the optimal excitation wavelength is 395 nm. At the same time, there are four emission bands of 576 nm (5D0→7F0), 596 nm (5D0→7F1), 658 nm (5D0→7F3), and 708 nm (5D0→7F4) that are observed. Compared with the scenario of the silicon substrate, the Eu-doped Si nanowires present strong red light emission. The photoluminescence properties of Eu-doped Si nanowires have potential applications in the lighting and the silicon optoelectronic integration. However, the parameters of Si nanowires such as diameter, density, surface morphology have great influences on the photoluminescence properties of Eu-doped Si nanowires, which are necessary to be further studied.

Non-aqueous sol–gel synthesis of hybrid rare-earth-doped γ-Ga2O3nanoparticles with multiple organic–inorganic-ionic light-emission features

Pure and Eu-doped γ-Ga2O3nanopowders with an organic capping layer were obtained by a benzyl alcohol route. Photoluminescence experiments allowed assigning the strong blue light emission to an aromatic ketone derivative.

Poly[(maleic anhydride)-alt-(vinyl acetate)]: A Pure Oxygenic Nonconjugated Macromolecule with Strong Light Emission and Solvatochromic Effect

Organic luminescent materials carrying no phenyl rings have attracted much interest from researchers due to their excellent biocompatibility and good biodegradability, which make them available for...

Large area growth and electrical properties of p-type WSe2 atomic layers.

Transition metal dichacogenides represent a unique class of two-dimensional layered materials that can be exfoliated into single or few atomic layers. Tungsten diselenide (WSe2) is one typical example with p-type semiconductor characteristics. Bulk WSe2 has an indirect band gap (∼1.2 eV), which transits into a direct band gap (∼1.65 eV) in monolayers. Monolayer WSe2, therefore, is of considerable interest as a new electronic material for functional electronics and optoelectronics. However, the controllable synthesis of large-area WSe2 atomic layers remains a challenge. The studies on WSe2 are largely limited by relatively small lateral size of exfoliated flakes and poor yield, which has significantly restricted the large-scale applications of the WSe2 atomic layers. Here, we report a systematic study of chemical vapor deposition approach for large area growth of atomically thin WSe2 film with the lateral dimensions up to ∼1 cm2. Microphotoluminescence mapping indicates distinct layer dependent efficiency. The monolayer area exhibits much stronger light emission than bilayer or multilayers, consistent with the expected transition to direct band gap in the monolayer limit. The transmission electron microscopy studies demonstrate excellent crystalline quality of the atomically thin WSe2. Electrical transport studies further show that the p-type WSe2 field-effect transistors exhibit excellent electronic characteristics with effective hole carrier mobility up to 100 cm2 V–1 s–1 for monolayer and up to 350 cm2 V–1 s–1 for few-layer materials at room temperature, comparable or well above that of previously reported mobility values for the synthetic WSe2 and comparable to the best exfoliated materials.

Yellow light emission from Ta2O5:Er, Eu, Ce thin films deposited using a simple co-sputtering method

Erbium, europium, and cerium co-doped tantalum oxide (Ta2O5:Er, Eu, Ce) thin films were prepared using a simple co-sputtering method, and yellow light emission was observed by the naked eye from a sample annealed at 900°C for 20min. The hexagonal Ta2O5 phase is very important, but the hexagonal CeTa7O19 phase should be avoided to obtain strong yellow light emission from Ta2O5:Er, Eu, Ce films. The co-sputtered films can be used as high-refractive-index and yellow-light-emitting materials of autocloned photonic crystals that can be applied to novel light-emission devices, and they will also be used as anti-reflection and down-conversion layers toward high-efficiency silicon solar cells.

Structure and optical properties of Dy3+/Tm3+ co-doped oxyfluoride glass ceramics containing β-NaGdF4 nanocrystals

Dy3+/Tm3+ co-doped oxyfluoride glass ceramics containing hexagonal β-NaGdF4 nanocrystals were prepared by the melt-quenching method and subsequent heat-treatment procedure. During the crystallization process, the structural evolution of glass network was systematically investigated using XRD, TEM and FTIR spectra. Experimental results provided new evidences that a silica-enriched layer around the precipitated fluoride nanocrystals was formed during the crystallization process. Strong white light emission was obtained in the oxyfluoride glass ceramics by modifying the relative concentration ratio of Tm3+ and Dy3+ ions.

Multiple Fireballs in a Reactive <inline-formula> <tex-math notation="TeX">${\rm H}_{2}/{\rm CH}_{4}$ </tex-math></inline-formula> Plasma

Inverted fireballs (FBs) are plasma phenomena, which develop inside a highly transparent, positively biased grid electrode through electron impact ionization. The ionizing electrons are accelerated into the grid by the high potential on the wires. This leads to an enhanced plasma density inside the hollow anode as well as a strong light emission. FBs show a wide variety of properties. This behavior may manifest itself in different shapes of FBs, which are very sensitive to the physical parameters of the discharge.

Suppression of Hole Overflow and Enhancement of Light Emission Efficiency in Si Quantum Dots Based Silicon Nitride Light Emitting Diodes

We present an effective method to suppress the hole overflow in Si quantum dots-based silicon nitride (SiN) light-emitting diodes (LEDs) by employing nanocrystalline Si (nc-Si) layer as hole blocking layer inserted between the SiN luminescent active layer and p-Si anode. The proposed devices exhibit strong white light emission under forward bias conditions. In comparison to the LEDs without nc-Si interlayer, a significant enhancement of more than 200% in light emission efficiency is achieved from the proposed devices. The increment in EL efficiency is found to strongly depend on the thickness of nc-Si interlayer. Besides, the proposed devices show a low turn-on voltage of 6 V, which is the same as that of the device without nc-Si interlayer. The analysis of the dominant recombination process indicates that the improved emission efficiency is resulting from the increased bimolecular radiative recombination probability, which is attributed to the effective hole-blocking effect of nc-Si barrier that mitigates the unbalance injections between electrons and holes in the SiN active layer by suppressing hole overflow.

InPBi single crystals grown by molecular beam epitaxy.

InPBi was predicted to be the most robust infrared optoelectronic material but also the most difficult to synthesize within In-VBi (V = P, As and Sb) 25 years ago. We report the first successful growth of InPBi single crystals with Bi concentration far beyond the doping level by gas source molecular beam epitaxy. The InPBi thin films reveal excellent surface, structural and optical qualities making it a promising new III–V compound family member for heterostructures. The Bi concentration is found to be 2.4 ± 0.4% with 94 ± 5% Bi atoms at substitutional sites. Optical absorption indicates a band gap of 1.23 eV at room temperature while photoluminescence shows unexpectedly strong and broad light emission at 1.4–2.7 μm which can't be explained by the existing theory.

White light emission of multi-chromophore photoluminescent nanoparticles using polyacrylate scaffold copolymers with pendent polyfluorene groups

Polyfluorenes and their nanoparticles are of interest because of their desirable photoluminescent properties. Here, we report the synthesis of a polyfluorene macromonomer p-[poly(9,9-dihexylfluorene-2,7-diyl] styrene (PFS) and their narrow polydispersity PFS-containing random copolymers with t-butyl acrylate [P(PFS-r-t-BA)s], i.e. via both reversible addition-fragmentation chain transfer (RAFT) and atom transfer radical polymerization (ATRP). The acid hydrolysis of P(PFS-r-t-BA) gives the corresponding amphiphilic P(PFS-r-acrylic acid) [P(PFS-r-AA)] polyelectrolytes, which self-assemble into photoluminescent nanoparticles in aqueous solutions. The P(PFS-r-AA) was shown to act as a scaffold for the incorporation of other pigments, which allowed tunable emissions via varying pigment combinations by Förster resonance energy transfer. The occurrence of strong white light emission was demonstrated.

Monophasic zircon-type tetragonal Eu1 − xBixVO4 solid-solution: synthesis, characterization, and optical properties

By combining the methods of co-precipitation and hydrothermal synthesis methods, the complete solid-solution of Eu1−xBixVO4 with monophasic zircon-type structure was successfully synthesized. The zircon-type structure was determined by X-ray diffractometer and Raman scattering, and the optical properties were characterized by ultraviolet-visible diffuse reflectance and photoluminescence spectrophotometer. The results indicate that the band gap of Eu1−xBixVO4 could be adjusted and controlled by bismuth content in the range of x=0–0.9. Meanwhile, the Eu1−xBixVO4 solid-solution phosphors show strong red light emission was shown in 619nm under both near UV-light and visible-light excitation. Notably, the emission intensity of Eu1−xBixVO4 (x=0.4) is the strongest in all samples.