White-light Photoluminescence Research Articles

Tunable and white light photoluminescence from ZnO on porous Si with the addition of carbon quantum dots.

In this work we demonstrate a two-pixel solid-state photoluminescent device able to emit white light covering the entire visible spectrum from 380 nm up to 800 nm. The device is based on a combination of porous Si, hydrothermally grown ZnO and carbon quantum dots, in a two-pixel formation, with porous Si and ZnO acting independently while the carbon quantum dots are deposited on top of the entire device. All processing is done using standard Si processing techniques. Moreover, the device design allows for tunability of the emitted spectrum simply by choosing the desired combination of the materials. Overall, the demonstrated device is low cost, environmentally safe and biocompatible.

Tunable white light photoluminescence of a single phase Tm3+/Tb3+/Eu3+ codoped GdPO4 phosphor

The present study describes the production of triply-doped GdPO4 and its optical characteristics. Structural information of the prepared material has been investigated by using X-ray diffraction and Fourier transform infrared spectroscopy. The material synthesized crystallizes into a single monoclinic crystal of space group P 21/n. The excitation curves of photoluminescence of single doped GdPO4: Tm3+, Tb3+, and Eu3+ are recorded and their emission spectra are analyzed. Triple-doped material emits multi colour light after a single UV stimulation. White light emission was seen in both triply-doped GdPO4 with variable Tm3+ concentration and triply-doped GdPO4 with variable Eu3+ concentration. GdPO4 doped with Tb3+ (7 mol%), Tm3+ (1.5 mol%), and Eu3+ (2 mol%) has colour coordinates (x = 0.3290, y = 0.3291) approximately near the value of typical white colour coordinates (x = 0.333, y = 0.3333). Furthermore, the transfer of energy in Tm3+, Tb3+ and Eu3+ in triple doped phosphor with varying Eu3+ concentrations was explained. Electric dipole-dipole interaction is used to justify and describe the process of energy transfer from Tb3+ to Eu3+. Decay time measurements were performed to explain energy transfer. Colour rendering index (CRI), Corelated colour temperature (CCT), Quantum efficiency and thermal stability of the prepared phosphor was calculated. All these parameters infer that GdPO4 doped with Tm3+, Tb3+ and Eu3+ may have potential application in white LEDs.

Boron‐Containing Molecules with Fluorescence‐Phosphorescence Dual‐Emission for Mechanochromism and Single Molecular White Light‐Emitting Diodes

AbstractOrganic molecules with fluorescence‐phosphorescence dual‐emission have attracted significant attention for their potential applications in white organic light‐emitting diodes (WOLEDs). Herein, donor–accepter molecules, Mes*BA‐Cz and FXylBA‐Cz, are designed and synthesized, and the photoluminescence of these two compounds in solid state exhibits fluorescence‐phosphorescence dual‐emission. Through the single crystal study, the phosphorescent emission is mainly caused by the molecular stacking in the crystalline state, which is beneficial for aggregation‐induced intersystem crossing. Dual emission behavior further caused the mechanochromism of the two compounds, with emission color changed between amorphous and crystalline state. White light photoluminescence with CIE coordinates of (0.33, 0.34) is achieved by doping FXylBA‐Cz in the poly (methyl methacrylate) film. Furthermore, a WOLED based on FXylBA‐Cz is manufactured with CIE coordinates of (0.31, 0.33), and the external quantum efficiency (EQE) reached 0.49%.

Dipole plasmon vitalized efficient white light emission via charge transfer in all oxide-based heterojunctions

Solid-state white-light emission, which is rapidly becoming the standard in a wide range of lighting applications, can be regarded as the best possible light source for next-generation cost-effective lighting. Herein, we report a simple solution-based technique to get efficient white-light emission using all-oxide semiconductor-based heterojunction. In this work, vertically oriented CuO nanorods were used for outstanding white-light emission by depositing ZnO thin films over CuO nanorods. The resulted bi-layered ZnO/CuO heterojunction arrangement have shown excellent optoelectronic properties. Furthermore, the inclusion of Au layer between ZnO/CuO heterojunction has improved white-light emission significantly and as an integral, a white light photoluminescence (PL) with a chromaticity coordinate of (0.32, 0.34) was obtained. Ab-initio calculations have supported our mechanism of charge transfer from CuO to ZnO especially with Au insertion. The presented work will provide insights into the intriguing optoelectronic properties of oxide hetero-structures.

White-light emitting multi-lanthanide terephthalate thin films by atomic/molecular layer deposition

ALD/MLD enables multi-lanthanide organic thin films in which different lanthanide species are optimally combined through organic linkers to yield warm white light photoluminescence.

A green and fast method for PEDOT: Photoinduced step-growth polymerization of EDOT

The first green and fast photoinduced step-growth polymerization of 3,4- ethylenedioxythiophene (EDOT) producing high molecular weight poly (3,4- ethylendioxythiophene) (PEDOT) is reported. Phenacyl bromide was used as a single-component photoinitiating system under a broad wavelength range. The reported photooxidative polymerization technique has several advantages over the conventional oxidation methods (chemical/electrochemical) such as the use of green solvent and ambient conditions (room temperature and air atmosphere), doping of the polymer with bromide ions during the photopolymerization reaction, possibility to perform bulk photopolymerization and tune the irradiation wavelength depending on the phenacyl bromide concentration. Doped PEDOT synthesized under near-UV irradiation was thoroughly investigated using different spectral and chromatographic methods. It has high conductivity (1.6 S/cm), high molecular weight (32.5 kg/mol) and strong white light photoluminescence.

Femtosecond Laser-Assisted Formation of Hybrid Nanoparticles from Bi-Layer Gold-Silicon Films for Microscale White-Light Source.

It is very natural to use silicon as a primary material for microelectronics. However, silicon application in nanophotonics is limited due to the indirect gap of its energy band structure. To improve the silicon emission properties, it can be combined with a plasmonic part. The resulting metal–dielectric (hybrid) nanostructures have shown their excellence compared to simple metallic dielectric nanostructures. Still, in many cases, the fabrication of such structures is time consuming and quite difficult. Here, for the first time, we demonstrate a single-step and lithography-free laser-induced dewetting of bi-layer nanoscale-thickness gold–silicon films supported by a glass substrate to produce hybrid nanoparticles. For obtaining hybrid nanoparticles, we study nonlinear photoluminescence by mapping their optical response and morphology by scanning electron microscopy. This method can be used for the fabrication of arrays of hybrid nanoparticles providing white-light photoluminescence with a good control of their microscopic sizes and position. The developed approach can be useful for a wide range of photonic applications including the all-optical data processing and storage where miniaturization down to micro- and nanoscale together with an efficiency increase is of high demand.

Correlating Broadband Photoluminescence with Structural Dynamics in Layered Hybrid Halide Perovskites.

The emission of white light from a single material is atypical and is of interest for solid-state lighting applications. Broadband light emission has been observed in some layered perovskite derivatives, A2PbBr4 (A = R-NH3+), and correlates with static structural distortions corresponding to out-of-plane tilting of the lead bromide octahedra. While materials with different organic cations can yield distinct out-of-plane tilts, the underlying origin of the octahedral tilting remains poorly understood. Using high energy resolution (e.g., quasi-elastic) neutron scattering, this contribution details the rotational dynamics of the organic cations in A2PbBr4 materials where A = n-butylammonium (nBA), 1,8-diaminooctammonium (ODA), and 4-aminobutyric acid (GABA). The organic cation dynamics differentiate (nBA)2PbBr4 from (ODA)PbBr4 or (GABA)2PbBr4 in that the larger spatial extent of dynamics of nBA yields a larger effective cation radius. The larger effective volume of the nBA cation in (nBA)2PbBr4 yields a closer to ideal A-site geometry, preventing the out-of-plane tilt and broadband luminescence. In all three compounds, we observe hydrogen dynamics attributed to rotation of the ammonium headgroup and at a time scale faster than the white light photoluminescence studied by time-correlated single photon counting spectroscopy. This supports a previous assignment of the broadband emission as resulting from a single ensemble, such that the emissive excited state experiences many local structures faster than the emissive decay. The findings presented here highlight the role of the organic cation and its dynamics in hybrid organic-inorganic perovskites and white light emission.

Liquid crystal polymers as luminescent coatings: Single-component white-light photoluminescence and corrosion inhibition

Luminescent coatings have several exciting applications. Polymers have been reported as both corrosion inhibitors and luminescent materials. Mild steel corrosion is a major economic problem. Moreover, full-color luminescence from one material is a hot research topic due to the advantages of such materials. Here, some liquid crystal polymers (LCPs) have been checked as corrosion inhibitors of mild steel in an acidic medium (1.0 M H2SO4) through potentiodynamic polarization techniques. The LCPs showed high anticorrosion efficiency depending on their structure. These LCPs were confirmed as mixed-type inhibitors. Furthermore, the studied LCPs have aggregation-induced emission behavior with controlled emission colors (blue, white, and green) via adjusting the solution concentration. The molecular aggregation changed according to the solution concentration, and thus the relative emission intensity was tuned at different wavelengths of the visible range. Interestingly, moderate solution concentrations displayed white emission from a single component. The LCPs also exhibited a stable emission behavior at high temperatures. Because these materials combine the advantages of polymers, LCs, corrosion inhibitors, and white-light emitters, these current findings should open a door to develop more attractive luminescent coatings.

"Зародышевые" трещины на поверхности кристалла кремния

The surface (100) of a silicon crystal after cutting the workpiece with a diamond disk and subsequent polishing was studied by the methods of white light interference profilometry and photoluminescence spectroscopy (PL). It was found that it is covered by "grooves". Their length is 10-40 µm, and the depth is quantized. It has values-1, 2.6, 3.6 and 4.5 nm. Four bands (1.63, 1.62, 1.68 and 2.25 eV) were observed in the PL spectra. They arise due to confinement, i.e., an increasing on the band gap width and a violation of momentum of the conservation law in nanocrystals. The sizes of nanocrystals are determined from the energy of the maxima of these bands. They are equal about 2, 2.3, 3 and 4 nm. When cutting silicon or striking it with a striker, fractoluminescence (FL) signals containing 4 maxima were observed. Signals are formed when dislocations break through barriers that occur at intersections.

Flexible-color tuning and white-light emission in three-, four-, and five-component host/guest co-crystals by charge-transfer emissions as well as effective energy transfers

A series of multi-color and white-light photoluminescence host/guest cocrystals were prepared by cooperative multi-molecular assemblies.

Multifunctional Ag nanoparticle decorated Si nanowires for sensing, photocatalysis and light emission applications

We report on the fabrication of Ag nanoparticle (NP) decorated mesoporous Si nanowire (NW) heterostructure (HS) by a simple and low cost chemical process. The as-grown Si NWs are mesoporous in nature and the Ag NP decorated Si NWs (Ag@Si NWs) exhibit broadband light emission, ultralow reflectance, efficient photocatalytic degradation of organic dyes and excellent sensitivity for the detection of organic molecules over a wide range of concentration. The broadband white light photoluminescence emission from the bare Si NWs is explained on the basis of quantum confinement effect in Si NCs/NWs and the nonbridging oxygen hole center defects in the SiSiOx interface. High work function of the noble metal NPs facilitates the effective separation of the photoinduced electron-hole pairs in Si NWs, which enables the Ag@Si NWs to exhibit high photocatalytic efficiency for the degradation of organic dye. The Ag@Si NWs exhibited high potential and sensitivity for the selective and quantitative detection of different organic molecules at extremely low concentration down to 10−12 M by surface-enhanced Raman scattering and 10−11 M by fluorescence-based detection. These versatile properties of the Ag@Si NWs open up opportunities for a variety of energy and environmental applications, such as white light emission, solar cell, artificial photosynthesis, disposal of organic pollutant and bio-chemical sensors etc.

Nearly white light photoluminescence from ZnO/rGO nanocomposite prepared by a one-step hydrothermal method

A zinc oxide (ZnO)/reduced graphene oxide (rGO) nanocomposite was prepared by a facile one-step hydrothermal method, i. e., the reduction from graphene oxide (GO) to rGO and the growing of ZnO nanocrystals on rGO were accomplished simultaneously. ZnO/rGO nanocomposite was proved to be made of flower-like ZnO nanocrystals enwrapped by rGO voiles. Under the excitation of ultraviolet light, the photoluminescence (PL) from ZnO/rGO exhibits a broad emission band spanned from ∼350 nm to ∼800 nm, and as an integral a nearly white light PL with a chromaticity coordinate of (∼0.25, ∼0.23) was obtained. Through Gaussian fitting process, the broad PL band was decomposed into six PL peaks, which were attributed to the radiative recombinations from ZnO and rGO, respectively. An analysis on the PL mechanism verified that the synergistic effect between the two constituent parts plays an important role in modulating the PL peak positions and intensities through enhancing or restraining the transport and transition process. Our experiments might provide an alternative path for preparing high-quality solid-state white light sources using ZnO/rGO as ultraviolet-activated phosphors.

Plasticity Promoted Band Structure Engineering Achieved by Arrayed Indentation on GaAs Wafers

Engineered defective sites on semiconductors offer opportunities for the design of novel optoelectronic devices with functions that are not intrinsically available. It is demonstrated that composite photonic crystal can be created on GaAs wafers by arrayed indentation. The indentation pattern supports photochemical cultivation of Ag nanoplates with a new principle involving plasticity promoted band engineering. It also provides a variety of novel functions not originally available in either GaAs or Ag nanostructures. In particular, this unique structure exhibits white light photoluminescence emission, strong enough to be perceived by the naked eye upon excitation with a 375 nm laser. This plasticity mediated principle opens a new avenue for the design and fabrication of novel composite semiconductor/metal structures with exotic properties.

White light emitting silicon nano-crystals-polymeric hybrid films prepared by single batch solution based method

Silicon nano-crystals have been studied intensively due to their photoluminescence properties and possible applications in new generation opto-electronic devices. Their importance in lightning and display technologies is increasing due to the abundance and non-toxicity of silicon. Here we report a single batch solution based synthesis route to silicon nano-crystal organic hybrid films exhibiting white light photoluminescence at room temperature upon excitation by ultraviolet light. Films prepared by ethylene glycol terminated Si nano-crystals showed maximum 240nm red shift in photoluminescence response upon excitation at 350nm. The shift was found to decrease in order for hybrid films fabricated using acrylic acid, 1-octanol acid and oleic acid terminated Si nano-crystals. The mean size of the Si nano-crystals (~2–10nm) estimated by Raman spectroscopy were smallest for the ethylene glycol capped Si nano-crystal films. The calculated Tauc bandgaps of the hybrid films varied between 1.51 and 2.35eV.

Easily processable multimodal spectral converters based on metal oxide/organic—inorganic hybrid nanocomposites

This manuscript reports the synthesis and characterization of the first organic–inorganic hybrid material exhibiting efficient multimodal spectral converting properties. The nanocomposite, made of Er3+, Yb3+ codoped zirconia nanoparticles (NPs) entrapped in a di-ureasil d–U(600) hybrid matrix, is prepared by an easy two-step sol-gel synthesis leading to homogeneous and transparent materials that can be very easily processed as monolith or film. Extensive structural characterization reveals that zirconia nanocrystals of 10–20 nm in size are efficiently dispersed into the hybrid matrix and that the local structure of the di-ureasil is not affected by the presence of the NPs. A significant enhancement in the refractive index of the di-ureasil matrix with the incorporation of the ZrO2 nanocrystals is observed. The optical study demonstrates that luminescent properties of both constituents are perfectly preserved in the final hybrid. Thus, the material displays a white-light photoluminescence from the di-ureasil component upon excitation at UV/visible radiation and also intense green and red emissions from the Er3+- and Yb3+-doped NPs after NIR excitation. The dynamics of the optical processes were also studied as a function of the lanthanide content and the thickness of the films. Our results indicate that these luminescent hybrids represent a low-cost, environmentally friendly, size-controlled, easily processed and chemically stable alternative material to be used in light harvesting devices such as luminescent solar concentrators, optical fibres and sensors. Furthermore, this synthetic approach can be extended to a wide variety of luminescent NPs entrapped in hybrid matrices, thus leading to multifunctional and versatile materials for efficient tuneable nonlinear optical nanodevices.

Tunable near white light photoluminescence of lanthanide ion (Dy3+, Eu3+and Tb3+) doped DNA lattices

We constructed lanthanide ion doped double-crossover DNA lattices grown on a silica substrate and studied their photoluminescence characteristics.

Nearly warm white-light emission of silicon-rich amorphous silicon carbide

An amorphous Si-rich SiC film with nearly warm white-light photoluminescence is synthesized to serve as a solid-state phosphorous material for white-lighting applications.

Nanoribbon-structured organo zinc phosphite polymorphs with white-light photoluminescence.

The first neutral organo zinc phosphites composed of 2.8 nm-wide ribbons were obtained in pure phases and exhibit near-white-light photoluminescence (PL). By using the "mesitylene strategy", interesting polymorphism in the system of NTHU-14 was discovered. The S-shaped ribbons are arranged into R and L arrays, resulting in RLR and RRR stacking for two polymorphs. π-π interactions exist within each array and hydrogen bonding between adjacent arrays. Besides a common ligand-based emission band at 410 nm, the PL curves of polymorphs 14-α and 14-β are distinctly different: 14-α gave a defect-based emission at 565 nm, whereas 14-β primarily shows a π-excimer-based emission at 535 nm. Electron paramagnetic resonance (EPR) data disclosed that radical species exist in the reaction and that the two phases were growing from different environments. Based on these results, the origin of the 565 nm band can be ascribed to lattice defects, and one possible cause of 14-β not showing noticeable yellow emission is identified.

Novel Sb3+/Eu3+ Co-doped phosphate luminescent glasses with adjustable emission

In the present work, the optical properties of Sb3+-doped and Sb3+/Eu3+ co-doped phosphate glasses were investigated. The blue emission intensity of Sb3+ decreased significantly while the red emission intensity of Eu3+ increased with the increasing concentration of Eu3+ ions. It was confirmed that an energy transfer from Sb3+ to Eu3+ occurred and the possible luminescent mechanism was proposed. The results suggest that the sensitization of Sb3+ not only enhance the emission intensity of Eu3+ excited at 274nm, but also results in the tunable emission color of the glasses. Particularly, white light photoluminescence combining blue and red emission was observed under ultraviolet light excitation.