Chlorides of NH₄Cl and SrCl₂ and fluorides of AlF₃ and SrF₂ were added to raw materials acting as the flux for preparing the SrSi₂O₂N₂:Eu²⁺ phosphor. The effects of the fluxes on the phase formation, particle morphology, particle size, and photoluminescence properties were investigated. The results revealed that particle size, particle morphology and photoluminescence intensity were largely dominated by the type of the flux material and its adding amount. The chloride-based flux was found to favor the formation of the SrSi₂O₂N₂:Eu²⁺ phase. Among the chloride-based fluxes, the sample added with the SrCl₂ flux presented the narrow particle distribution and cleaner surface, with enhanced emission intensity and an increased external quantum efficiency by 68% and 22%, respectively, compared with those of the sample without any flux adding. Full article

Many studies have considered the luminescence of colloidal II–VI nanocrystals, both in solution at a collective scale and at an individual scale by confocal microscopy. The quantum yield is an important figure of merit for the optical quality of a fluorophore. We detail here a simple method to determine the quantum yield of nanocrystals in solution as a function of the absorption. For this purpose, we choose rhodamine 101 as a reference dye to measure the nanocrystal fluorescence quantum yield. The influence of the concentration on quantum yield is therefore studied for both the reference and the solutions of nanocrystals and is found to be critical for the acuity of the method. Different types of nanocrystals are studied to illustrate different quantum yield evolutions with the concentration. Full article

Green-emitting phosphors based on lanthanum-gadolinium oxybromide were synthesized in a single phase form by the conventional solid state reaction method, and photoluminescence properties of them were characterized. The excitation peak wavelength of (La_1-xGd_x)OBr:Tb³⁺ shifted to the shorter wavelength side with the increase in the crystal field around the Tb³⁺ ions by doping Gd³⁺ ions into the La³⁺ site, and, as a result, the green emission intensity was successfully enhanced. The maximum emission intensity was obtained for (La_0.95Gd_0.05)OBr:5%Tb³⁺, where the relative emission intensity was 45% of that of a commercial green-emitting LaPO₄:Ce³⁺,Tb³⁺ phosphor. Full article

We numerically depict the complete angular distributions of luminescence and absorption properties in biaxial media, by calculating the imaginary part of the optical index for all directions of propagation. Our simulations show a double-layer surface with specific topology and symmetry properties that greatly differ from those of the refractive index surface. Our calculations show that the two layers intersect and inverse themselves along continuous loci related to polarization-independent luminescence or absorption properties. Specificities related to the orthorhombic, monoclinic and triclinic biaxial crystal systems are discussed. Such theoretical developments should be considered to fully exploit innovating luminescent materials. Full article

The quantum cutting phenomenon of a blue photon into two infrared photons is reported in glass codoped with Pr³⁺-Yb³⁺ ions. Oxyfluoride glass with compositions of 32SrF₂-0.1PrF₃-2.9YbF₃-42SiO₂-23Al₂O₃ were prepared, and photoluminescence properties in the range from visible to near-infrared were investigated. Evidence of several energy transfers, such as (Pr³⁺:³P₀→¹G₄)→(Yb³⁺:²F_5/2←²F_7/2) and (Pr³⁺:¹D₂→³F₄, ³F₃)→(Yb³⁺:²F_5/2←²F_7/2), were demonstrated in the Pr³⁺-Yb³⁺ co-doped glass. By comparing excitation spectrum of the Yb³⁺ emission with absorption spectrum of Pr³⁺, we obtain direct evidence of quantum cutting by excitation to Pr³⁺:³P_J levels at 420 ~ 490 nm. Full article

The crystal structure and the photoluminescence properties of novel green Ba_4-yEu_ySi₆O_16-3x/2N_x phosphors were investigated. The electronic structures of the Ba₄Si₆O₁₆ host were calculated by first principles pseudopotential method based on density functional theory. The results reveal that the top of the valence bands are dominated by O-2p states hybridized with Ba-6s and Si-3p states, while the conduction bands are mainly determined by Ba-6s states for the host, which is an insulator with a direct energy gap of 4.6 eV at Γ. A small amount of nitrogen can be incorporated into the host to replace oxygen and forms Ba_4-yEu_ySi₆O_16-3x/2N_x solid solutions crystallized in a monoclinic (space group P2₁/c, Z = 2) having the lattice parameters a = 12.4663(5) Å, b = 4.6829(2) Å, c = 13.9236(6) Å, and β = 93.61(1)°, with a maximum solubility of nitrogen at about x = 0.1. Ba₄Si₆O_16-3x/2N_x:Eu²⁺ exhibits efficient green emission centered at 515–525 nm varying with the Eu²⁺ concentration when excited under UV to 400 nm. Furthermore, the incorporation of nitrogen can slightly enhance the photoluminescence intensity. Excitation in the UV-blue spectral range (λ_exc = 375 nm), the absorption and quantum efficiency of Ba_4-yEu_ySi₆O_16-3x/2N_x (x = 0.1, y = 0.2) reach about 80% and 46%, respectively. Through further improvement of the thermal stability, novel green phosphor of Ba_4-yEu_ySi₆O_16-3x/2N_x is promising for application in white UV-LEDs. Full article

An in-depth optimization of growth conditions and investigation of optical properties including discussions on band alignment of GaAsSb/GaAs quantum well (QW) on GaAs by molecular beam epitaxy (MBE) are reported. Optimal MBE growth temperature of GaAsSb QW is found to be 470 ± 10 °C. GaAsSb/GaAs QW with Sb content ~0.36 has a weak type-II band alignment with valence band offset ratio Q_V ~1.06. A full width at half maximum (FWHM) of ~60 meV in room temperature (RT) photoluminescence (PL) indicates fluctuation in electrostatic potential to be less than 20 meV. Samples grown under optimal conditions do not exhibit any blue shift of peak in RT PL spectra under varying excitation. Full article

The paper proposes novel molecular designs for rare-earth complexes involving the introduction of two different phosphine oxide structures into one rare-earth ion. These designs are effective for improving solubility and emission intensity. Additionally, the complexes are indispensable for realizing high performances in LEDs and security media. The thermodynamic properties of Eu(III) complexes are correlated with the solubility. Correlations between coordination structures and emission intensity were explained by NMR analysis. The luminous flux of red LED devices with Eu(III) complexes is very high (20 mA, 870 m lumen). A new white LED has its largest spectra intensity in the red region and a human look much more vividly under this light. Full article

Nitridosilicates are structurally built up on three-dimensional SiN4 tetrahedral networks, forming a very interesting class of materials with high thermomechanical properties, hardness, and wide band gap. Traditionally, nitridosilicates are often used as structural materials such as abrasive particles, cutting tools, turbine blade, etc. Recently, the luminescence of rare earth doped nitridosilicates has been extensively studied, and a novel family of luminescent materials has been developed. This paper reviews the synthesis, luminescence and applications of nitridosilicate phosphors, with emphasis on rare earth nitrides in the system of M-Si-Al-O-N (M = Li, Ca, Sr, Ba, La) and their applications in white LEDs. These phosphors exhibit interesting luminescent properties, such as red-shifted excitation and emission, small Stokes shift, small thermal quenching, and high conversion efficiency, enabling them to use as down-conversion luminescent materials in white LEDs with tunable color temperature and high color rendering index. Full article

This article reviews the synthesis, structural and optical characterizations of some novel luminescent two dimensional organic-inorganic perovskite (2DOIP) semiconductors. These 2DOIP semiconductors show a self-assembled nano-layered structure, having the electronic structure of multi-quantum wells. 2DOIP thin layers and nanoparticles have been prepared through different methods. The structures of the 2DOIP semiconductors are characterized by atomic force microscopy and X-ray diffraction. The optical properties of theb DOIP semiconductors are characterized from absorption and photoluminescence spectra measured at room and low temperatures. Influences of different components, in particular the organic parts, on the structural and optical properties of the 2DOIP semiconductors are discussed. Full article

Sulfide-based luminescent materials have attracted a lot of attention for a wide range of photo-, cathodo- and electroluminescent applications. Upon doping with Ce³⁺ and Eu²⁺, the luminescence can be varied over the entire visible region by appropriately choosing the composition of the sulfide host. Main application areas are flat panel displays based on thin film electroluminescence, field emission displays and ZnS-based powder electroluminescence for backlights. For these applications, special attention is given to BaAl₂S₄:Eu, ZnS:Mn and ZnS:Cu. Recently, sulfide materials have regained interest due to their ability (in contrast to oxide materials) to provide a broad band, Eu²⁺-based red emission for use as a color conversion material in white-light emitting diodes (LEDs). The potential application of rare-earth doped binary alkaline-earth sulfides, like CaS and SrS, thiogallates, thioaluminates and thiosilicates as conversion phosphors is discussed. Finally, this review concludes with the size-dependent luminescence in intrinsic colloidal quantum dots like PbS and CdS, and with the luminescence in doped nanoparticles. Full article

Zinc oxide (ZnO) is a strong luminescent material, as are several polymers. These two materials have distinct drawbacks and advantages, and they can be combined to form nanostructures with many important applications, e.g., large-area white lighting. This paper discusses the origin of visible emission centers in ZnO nanorods grown with different approaches. White light emitting diodes (LEDs) were fabricated by combining n-ZnO nanorods and hollow nanotubes with different p-type materials to form heterojunctions. The p-type component of the hybrids includes p-SiC, p-GaN, and polymers. We conclude by analyzing the electroluminescence of the different light emitting diodes we fabricated. The observed optical, electrical, and electro-optical characteristics of these LEDs are discussed with an emphasis on the deep level centers that cause the emission. Full article

In 1996, Matsuzawa et al. reported on the extremely long-lasting afterglow of SrAl₂O₄:Eu²⁺ codoped with Dy³⁺ ions, which was more than 10-times brighter than the previously widely used ZnS:Cu,Co. Since then, research for stable and efficient persistent phosphors has continuously gained popularity. However, even today - almost 15 years after the discovery of SrAl₂O₄:Eu²⁺, Dy³⁺ - the number of persistent luminescent materials is still relatively low. Furthermore, the mechanism behind this phenomenon is still unclear. Although most authors agree on the general features, such as the existence of long-lived trap levels, many details are still shrouded in mystery. In this review, we present an overview of the important classes of known persistent luminescent materials based on Eu²⁺-emission and how they were prepared, and we take a closer look at the models and mechanisms that have been suggested to explain bright afterglow in various compounds. Full article

Semiconducting quantum dots, whose particle sizes are in the nanometer range, have very unusual properties. The quantum dots have band gaps that depend in a complicated fashion upon a number of factors, described in the article. Processing-structure-properties-performance relationships are reviewed for compound semiconducting quantum dots. Various methods for synthesizing these quantum dots are discussed, as well as their resulting properties. Quantum states and confinement of their excitons may shift their optical absorption and emission energies. Such effects are important for tuning their luminescence stimulated by photons (photoluminescence) or electric field (electroluminescence). In this article, decoupling of quantum effects on excitation and emission are described, along with the use of quantum dots as sensitizers in phosphors. In addition, we reviewed the multimodal applications of quantum dots, including in electroluminescence device, solar cell and biological imaging. Full article

Zinc oxide (ZnO) is a potential candidate material for optoelectronic applications, especially for blue to ultraviolet light emitting devices, due to its fundamental advantages, such as direct wide band gap of 3.37 eV, large exciton binding energy of 60 meV, and high optical gain of 320 cm⁻¹ at room temperature. Its luminescent properties have been intensively investigated for samples, in the form of bulk, thin film, or nanostructure, prepared by various methods and doped with different impurities. In this paper, we first review briefly the recent progress in this field. Then a comprehensive summary of the research carried out in our laboratory on ZnO preparation and its luminescent properties, will be presented, in which the involved samples include ZnO films and nanorods prepared with different methods and doped with n-type or p-type impurities. The results of ZnO based LEDs will also be discussed. Full article

White light-emitting diodes (WLEDs) have matched the emission efficiency of florescent lights and will rapidly spread as light source for homes and offices in the next 5 to 10 years. WLEDs provide a light element having a semiconductor light emitting layer (blue or near-ultraviolet (nUV) LEDs) and photoluminescence phosphors. These solid-state LED lamps, rather than organic light emitting diode (OLED) or polymer light-emitting diode (PLED), have a number of advantages over conventional incandescent bulbs and halogen lamps, such as high efficiency to convert electrical energy into light, reliability and long operating lifetime. To meet with the further requirement of high color rendering index, warm light with low color temperature, high thermal stability and higher energy efficiency for WLEDs, new phosphors that can absorb excitation energy from blue or nUV LEDs and generate visible emissions efficiently are desired. The criteria of choosing the best phosphors, for blue (450-480 nm) and nUV (380-400 nm) LEDs, strongly depends on the absorption and emission of the phosphors. Moreover, the balance of light between the emission from blue-nUV LEDs and the emissions from phosphors (such as yellow from Y₃Al₅O₁₂:Ce³⁺) is important to obtain white light with proper color rendering index and color temperature. Here, we will review the status of phosphors for LEDs and prospect the future development. Full article

This paper reviews the synthesis, structure and applications of metal fluoride nanoparticles, with particular focus on rare earth (RE) doped fluoride nanoparticles obtained by our research group. Nanoparticles were produced by precipitation methods using the ligand ammonium di-n-octadecyldithiophosphate (ADDP) that allows the growth of shells around a core particle while simultaneously avoiding particle aggregation. Nanoparticles were characterized on their structure, morphology, and luminescent properties. We discuss the synthesis, properties, and application of heavy metal fluorides; specifically LaF₃:RE and PbF₂, and group IIA fluorides. Particular attention is given to the synthesis of core/shell nanoparticles, including selectively RE-doped LaF₃/LaF₃, and CaF₂/CaF₂ core/(multi-)shell nanoparticles, and the CaF₂-LaF₃ system. Full article

At present, thick film (powder based) alternating current electroluminescence (AC-EL) is the only technology available for the fabrication of large area, laterally structured and coloured light sources by simple printing techniques. Substrates for printing may be based on flexible polymers or glass, so the final devices can take up a huge variety of shapes. After an introduction of the underlying physics and chemistry, the review highlights the technical progress behind this development, concentrating on luminescent and dielectric materials used. Limitations of the available materials as well as room for further improvement are also discussed. Full article

Although photoluminescence from gallium-arsenide (GaAs) deep-centers was first observed in the 1960s, semiconductor lasers have always utilized conduction-to-valence-band transitions. Here we review recent materials studies leading to the first GaAs deep-center laser. First, we summarize well-known properties: nature of deep-center complexes, Franck-Condon effect, hotoluminescence. Second, we describe our recent work: insensitivity of photoluminescence with heating, striking differences between electroluminescence and photoluminescence, correlation between transitions to deep-states and absence of bandgap-emission. Room-temperature stimulated-emission from GaAs deep-centers was observed at low electrical injection, and could be tuned from the bandgap to half-the-bandgap (900–1,600 nm) by changing the electrical injection. The first GaAs deep-center laser was demonstrated with electrical injection, and exhibited a threshold of less than 27 mA/cm2 in continuous-wave mode at room temperature at the important 1.54 μm fiber-optic wavelength. This small injection for laser action was explained by fast depopulation of the lower state of the optical transition (fast capture of free holes onto deep-centers), which maintains the population inversion. The evidence for laser action included: superlinear L-I curve, quasi-Fermi level separations satisfying Bernard-Duraffourg’s criterion, optical gains larger than known significant losses, clamping of the optical-emission from lossy modes unable to reach laser action, pinning of the population distribution during laser action. Full article