White-light Photoluminescence Research Articles

Tunable Multicolor Emission and Energy Transfer of Sb3+/Mn2+ Codoped Phosphate Glasses by Design

In this work, the luminescent properties of Sb3+/Mn2+ codoped 60P2O5–40MgO glass are presented. White light photoluminescence combining blue and orange‐red light was observed under ultraviolet light excitation. The emission spectra showed that the blue emission intensity of Sb3+ decreased significantly whereas the red emission intensity of Mn2+ increased with the increasing concentration of Mn2+ ions. Meanwhile, by maintaining the concentration of MnO (2.0 mol%) and increasing concentration of Sb2O3, both the blue emission and red emission were enhanced remarkably. The energy transfer from Sb3+ to Mn2+ ions via the dipole–quadrupole interaction was confirmed.

White-light photoluminescence and photoactivation in cadmium sulfide embedded in mesoporous silicon dioxide templates studied by confocal laser scanning microscopy

SBA-15 and SBA-16 silica templates have been infiltrated with CdS by means of nanocasting using a hybrid precursor. The morphology and structure of both the SiO2@CdS nanocomposites and the silica-free CdS replicas have been characterized. The three-dimensional nanocrystalline CdS networks embedded in SBA-15 and SBA-16 silica templates exhibit broad photoluminescence (PL) spectra over the entire visible range, together with enhanced PL intensity compared to silica-free CdS replicas. These effects result from the role silica plays in passivating the surface of the CdS mesostructures. Furthermore, photoactivation is eventually observed during continuous illumination because of both structural and chemical surface modifications. Owing to this combination of properties, these materials could be appealing for solid-state lighting, where ultra-bright near-white PL emission is indispensable.

Preparation and Characteristics of Ca2NaMg2V3O12:Sm3+ Single-Phased White-Emitting Phosphors

Novel single-phased phosphors Ca2NaMg2-V3O12:xSm3+ that exhibit efficient white-light photoluminescence properties have been successfully synthesized by the solid-state reaction method. The formation of a single Ca2NaMg2V3O12 phase has been confirmed by X-ray powder diffraction (XRD). The wavelength-tunable white light is realized by coupling of the broad emission band at 500 nm due to a V5+−O2− charge-transfer state transition and the sharp emission peaks at 564, 616, 650 and 708 nm assigned to 4G5/2→6HJ (J = 5/2, 7/2, 9/2, 11/2) transitions of the Sm3+ ion. The luminescence color can be tuned from green to white by adjusting the doping concentration of Sm3+. When the doping concentration of Sm3+is increased from x = 0 to x = 0.20, the color rendering index of the Ca2NaMg2V3O12:xSm3+ phosphors increased from 55 to 83. The present white phosphors show a great potential for white LEDs.

Crystalline Inorganic Frameworks with 56-Ring, 64-Ring, and 72-Ring Channels

The development of zeolite-like structures with extra-large pores (>12-membered rings, 12R) has been sporadic and is currently at 30R. In general, templating via molecules leads to crystalline frameworks, whereas the use of organized assemblies that permit much larger pores produces noncrystalline frameworks. Synthetic methods that generate crystallinity from both discrete templates and organized assemblies represent a viable design strategy for developing crystalline porous inorganic frameworks spanning the micro and meso regimes. We show that by integrating templating mechanisms for both zeolites and mesoporous silica in a single system, the channel size for gallium zincophosphites can be systematically tuned from 24R and 28R to 40R, 48R, 56R, 64R, and 72R. Although the materials have low thermal stability and retain their templating agents, single-activator doping of Mn(2+) can create white-light photoluminescence.

Ethylenediamine assisted synthesis of wurtzite zinc sulphide nanosheets and porous zinc oxide nanostructures: near white light photoluminescence emission and photocatalytic activity under visible light irradiation

Porous fungus-like ZnO nanostructures have been synthesized by simple thermal annealing of the hydrothermally synthesized sheet-like ZnS(en)0.5 complex precursor in air at 600 °C. Structural and morphological changes occurring during ZnS(en)0.5 → ZnS → ZnO transformations have been observed closely by annealing the as-synthesized precursor at 100–600 °C. Wurtzite ZnS nanosheets and ZnS–ZnO composites are obtained at temperatures of 400 °C and 500 °C, respectively. Thermal decomposition and oxidation of the ZnS(en)0.5 nanosheets have been confirmed by differential scanning calorimetry and thermo-gravimetric analysis. The visible light driven photocatalytic degradation of methylene blue dye has been demonstrated in the synthesized samples. ZnS–ZnO composite shows the highest dye degradation efficiency of 74% due to the formation of surface complex as well as higher visible light absorption as a result of band-gap narrowing effect. The porous ZnO nanostructures show efficient visible photoluminescence (PL) emission with a colour coordinate of (0.29, 0.35), which is close to that of white light (0.33, 0.33). The efficient visible PL emission as well as visible light driven photocatalytic activity of the materials synthesized in the present work might be very attractive for their applications in future optoelectronic devices, including in white light emitting devices.

Metal-Free Highly Luminescent Silica Nanoparticles

Stable, cost-effective, brightly luminescent, and metal-free organosilica nanoparticles (NPs) were prepared using the Stöber method without any thermal treatment above 318 K. The white-light photoluminescence results from a convolution of the emission originated in the NH(2) groups of the organosilane and oxygen defects in the silica network. The time-resolved emission spectra are red-shifted, relative to those acquired in the steady-state regime, pointing out that the NPs emission is governed by donor-acceptor (D-A) recombination mechanisms. Moreover, the increase of the corresponding lifetime values with the monitored wavelength further supports that the emission is governed by a recombination mechanism typical of a D-A pair attributed to an exceptionally broad inhomogeneous distribution of the emitting centers peculiar to silica-based NPs. These NPs exhibit the highest emission quantum yield value (0.15 ± 0.02) reported so far for organosilica biolabels without activator metals. Moreover, the emission spectra and the quantum yield values are quite stable over time showing no significant aging effects after exposure to the ambient environment for more than 1 year, stressing the potential of these NPs as metal-free biolabels.

Effects of source material on epitaxial growth of fluorescent SiC

The growth of fluorescent SiC using Fast Sublimation Growth Process was demonstrated using different types of SiC source materials. These were prepared by (i) high-temperature hot pressing, (ii) chemical vapor deposition and (iii) physical vapor transport. The optimized growth rates of 50μm/h, 170μm/h and 200μm/h were achieved using the three types of sources, respectively. The best results in respect to growth rates are obtained using higher density sources. Fluorescent SiC layers with mirror-like morphology, very good crystal quality and yellowish or warm white light photoluminescence at room temperature were grown using all three types of the source materials.

Rhodamine B-anchored silica nanoparticles displaying white-light photoluminescence and their uses in preparations of photoluminescent polymeric films and nanofibers

This work reports white-light photoluminescent (PL) silica nanoparticles and their applications of preparation of PL polymer films and nanofibers. Rhodamine B (RhB) physically adsorbs or chemically bonds to silica nanoparticle (SNP) surfaces, resulting in PL SNPs. The RhB-modified SNPs exhibit white-light PL emissions under an excitation at 365 nm, which is different from the inherent yellow light emission of RhB. The SNPs with physically-adsorbed RhB show stimuli-responsive properties. In solutions, the RhB molecules which physically adsorb to SNPs release from SNPs, consequently turning the PL emission from white-light to yellow. On the other hand, the SNPs having covalently-bonded-RhB molecules are effective additives for preparation of white-light PL polymer composites. Both PL poly(methylmethacrylate) (PMMA) films (from casting process) and nanofibers (from electrospinning process) showing white-light PL emission have been prepared.

White light photoluminescence from ZnS films on porous Si substrates

ZnS films were deposited on porous Si (PS) substrates using a pulsed laser deposition (PLD) technique. White light emission is observed in photoluminescence (PL) spectra, and the white light is the combination of blue and green emission from ZnS and red emission from PS. The white PL spectra are broad, intense in a visible band ranging from 450 to 700 nm. The effects of the excitation wavelength, growth temperature of ZnS films, PS porosity and annealing temperature on the PL spectra of ZnS/PS were also investigated.

CaAl[sub 2]O[sub 4]:Eu[sup 2+],Nd[sup 3+],Sr[sup 2+]: A White-Light Phosphor with Yellow-Green Long Afterglow

A CaAl 2 O 4 :Eu 2+ ,Nd 3+ ,Sr 2+ phosphor, with white light under irradiation and a yellow-green long afterglow, was prepared by the solid-state method. The emission spectra, afterglow spectra, and afterglow decay curve of the samples have been measured. It is found that the emission spectra under the irradiation of 400 nm are comprised of the blue-light emission (442 nm) and the yellow-green-light emission (538 nm), and the chromaticity coordinates were calculated to be x = 0.289, y = 0.341. After the irradiation source was removed, the blue emission decreased rapidly so that the white-light photoluminescence changed to the yellow-green afterglow and its persistent time was measured to be over 4 h.

Morphology-Controlled Synthesis, Physical Characterization, and Photoluminescence of Novel Self-Assembled Pomponlike White Light Phosphor: Eu3+-Doped Sodium Gadolinium Tungstate

Three-dimensional pomponlike europium-doped sodium gadolinium tungstate NaGdWO4(OH)x:Eu3+ microarchitectures that exhibit efficient white-light photoluminescence properties have been successfully synthesized via a facile hydrothermal process in the presence of the surfactants cetyl trimethyl ammonium bromide, poly(vinyl pyrrolidone), and poly(ethylene glycol)-block-poly(propylene glycol)-block-ploy(ethylene glycol). The white light sodium gadolinium tungstate phosphor contains three emission bands: the blue-green band at 468 nm is ascribed to the ligand to metal charge transfer transition from O→W; the orange band at 590 nm and red band at 610 nm are attributed to the 5D0→7F1 and 5D0→7F2 transitions of Eu3+. The luminescence color can be tuned from blue to white to red by adjusting the doping concentration of Eu3+. Both scanning electron and transmission electron microscopy indicate that the obtained microspheres have a uniform particle size distribution. The three-dimensional sodium gadolium tungstate pompon-shaped structures were constructed layer-by-layer from a large number of two-dimensional nanoflakes with a mean diameter of ∼100 nm. The whole time-dependent process is interpreted as an example of self-assembly process. The emission spectra are dominated by a 5D0→7F2 transition of Eu3+. The optimum concentration for the white light was to keep the ratio of Eu3+ and Gd3+ at about 0.02.

Energy Transfer and Emission Quantum Yields of Organic−Inorganic Hybrids Lacking Metal Activator Centers

This work discusses quantitatively the energy transfer mechanism that occurs in the white-light emission of sol−gel derived amine- and amide-functionalized hybrids. The white-light photoluminescence (PL) results from a convolution of the emission originated in the NH/CO groups of the organic/inorganic cross-links with electron-hole recombinations occurring in the siloxane nanoclusters, both emissions typical of donor−acceptor pairs. Two model compounds that reproduce separately the two hybrid's emissions were synthesized and characterized by X-ray diffraction, 29Si/1H/13C magic-angle spinning NMR, diffuse reflectance, Fourier transform−IR, and photoluminescence spectroscopy to support their use as organic and inorganic structural models for the two counterparts of the hybrids. The comparison between the lifetimes of the two emissions of the inorganic and organic model compounds with those of the hybrids, the Arrhenius dependence with temperature of the siliceous-related lifetime in the hybrids, and the no...

White-Light Emission of Amine-Functionalized Organic/Inorganic Hybrids: Emitting Centers and Recombination Mechanisms

This work discusses the recombination mechanisms and the chemical nature of the emitting centers subjacent to the white-light emission of sol−gel derived amine-functionalized hybrids lacking metal activator ions, such as those based on 3-aminopropyl)triethoxysilane (APTES), 3-glycidyloxypropyltrimethoxysilane (GPTES), and on urea and urethane precursors. The white-light photoluminescence (PL) results from a convolution of the emission originated in the NH (NH2) groups of the urea or urethane bridges (APTES- and GPTES-based hybrids) with electron−hole recombinations occurring in the siloxane nanoclusters. These two components reveal a radiative recombination mechanism typical of donor−acceptor pairs, mediated by some localized centers. Photoinduced proton-transfer between defects such as NH3+ and NH- (GPTES- and APTES-based hybrids) or NH2+ and N- (di-ureasils and di-urethanesils) is proposed as the mechanism responsible for the NH-related component. Electron paramagnetic resonance data suggest that the sp...

Synthesis of Nano-ZnS Modified Porous Si with White Light Photoluminescence Properties

Porous silicon (PS) was modified with nano-ZnS using a chemical method. Scanning electron microscopy (SEM) images show that after the modification, smaller nano-ZnS particles 10–50 nm in diameter appear in the PS host. The formation of nano-ZnS in PS was also confirmed by energy dispersive spectroscopy (EDS). The EDS results revealed that the same ratio of Zn and S atoms existed in PS after the deposition of ZnS. Photoluminescence spectra of nano-ZnS/PS structures exhibited a distinct shift of emission from red to blue with increasing ZnS coverage. With appropriate doping, it is possible to obtain white light photoluminescence from nano-ZnS/PS.

White light luminescence from nano-ZnS doped porous silicon

Nano-ZnS was deposited into porous silicon. By varying theconcentration of Zn2+ ion solution during nano-ZnS formation,the amount of nano-ZnS in the porous silicon host can be controlled.The doped porous silicon exhibited a gradual shift in itsphotoluminescence peak from red to blue as a function of the nano-ZnScoverage. At an optimum doping, white light photoluminescence wasobtained. A study in the luminescence lifetime has shown that theradiative recombination at the blue end of the visible spectrum wasdue to nano-ZnS, whereas luminescence emission at the red end of thevisible spectrum came from porous silicon. The latter luminescencewas due to the tunnelling of excited electrons from nano-ZnS intoporous silicon. Time-resolved photoluminescence has also shown thatradiative recombination was effectively dominated by the nano-ZnS.The photoluminescence excitation results revealed the presence of twoexcitation levels: one belonging to nano-ZnS at the near-ultravioletregion, and another at about 520 nm from the surface states of poroussilicon. The doping of nano-ZnS into porous silicon demonstrates thatluminescence colour tuning is possible when an appropriate functionalmaterial is introduced into porous silicon.

White Light Luminescence from Nano-ZnS Doped Porous Silicon

Nano-ZnS was deposited into porous silicon. By varying the concentration of Zn2+ ion solution during nano-ZnS formation, the amount of nano-ZnS in porous silicon host can be controlled. The doped porous silicon exhibited a gradual shift in its photoluminescence peak from red to blue as a function of the nano-ZnS coverage. At an optimum doping, white light photoluminescence was obtained. A study in the luminescence lifetime showed that the radiative recombination at the blue end of the visible spectrum was due to nano-ZnS, whereas, luminescence emission at the red end of the visible spectrum came from porous silicon. The latter luminescence was due to in part tunneling of excited electrons from nanoZnS into porous silicon and in part direct excitation of porous silicon layer. Time-resolved photoluminescence also showed that radiative recombination was effectively dominated by the nano-ZnS. Photoluminescence excitation result revealed the presence of two excitation levels; one belonged to nano-ZnS at near uv region, and another at about 520 nm from the surface states of porous silicon and nano-ZnS. The doping of nano-ZnS into porous silicon demonstrates that luminescence color tuning is possible when an appropriate functional material is introduced into porous silicon.

Chemiluminescence and photoluminescence of S 2, SO and SO 2 in SF 6 afterglows

Frequently, the success of producing short-lived chemical species for use in chemical kinetic studies or for obtaining spectroscopic data depends on the chance finding of a source which gives high density of molecules. This paper describes methods of obtaining chemiluminescence of S 2, SO and SO 2 molecules, and, as well, sufficiently large concentrations of these species in their ground states to make possible the spectroscopic study by white light photoluminescence. A mixture of sulfur hexafluoride in helium passing through a microwave discharge serves as a source of these reactive atoms and molecules.