Photoluminescent materials

The phosphor MgW04 is an example of a luminescent material with 100% activator concentration, since each octahedral tungstate group in the lattice is able to luminesce. However, there is no concentration quenching. This is due to the large 

The broadness of the (Zn,Be)2Si04 Mn emission is due to another reason. Actually the emission of beryllium-free Zn2Si04 Mn is narrow (Fig. 6.5). Let us, therefore, start with the latter phosphor which shows a bright-grocn emission. 

If we replace part of the Zn ions by Be ions, the crystal field on the Mn ions will vary from ion to ion depending on the nature of the neighboring metal ions. This is due to the large difference between the ionic radii of Zn + and Be (0.60 Aand 0.27 A, respectively). Therefore, the emission band broadens relative to that of Zn2Si04 Obviously the introduction of Be increases the crystal field 

A serious drawback of this Mn phosphor is its poor maintenance in a lamp. It easily picks up mercury from the gas discharge and is liable to decompose under ultraviolet radiation. In addition beryllium is highly toxic [7], and nowadays not acceptable for application. In 1948, these phosphors were replaced by one phosphor with blue and orange emission, viz. Sb - and Mn -activated calcium halophosphate. 

Jenkings et al. [12] discovered that Sb -doped calcium halophosphate is a very efficient blue-emitting phosphor under 254 excitation (sec Fig. 6.6). The Sb ion has 5s configuration and its Su — P and P absorption bands are situated at 255 and 205 nm, respectively (F ig. 6.7) [II]. The Stokes shift of the emission is enormous, viz. 19000 cm at room temperature. 

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A Montali, C Bastiaansen, P Smith, and C Weder, Polarizing energy transfer in photoluminescent materials for display applications, Nature, 392 261-264, 1998. 

The first chemical transformations carried out with Cjq were reductions. After the pronounced electrophilicity of the fullerenes was recognized, electron transfer reactions with electropositive metals, organometallic compounds, strong organic donor molecules as well as electrochemical and photochemical reductions have been used to prepare fulleride salts respectively fulleride anions. Functionalized fulleride anions and salts have been mostly prepared by reactions with carbanions or by removing the proton from hydrofullerenes. Some of these systems, either functionalized or derived from pristine Cjq, exhibit extraordinary solid-state properties such as superconductivity and molecular ferromagnetism. Fullerides are promising candidates for nonlinear optical materials and may be used for enhanced photoluminescence material. 

In general, the photoluminescent properties of molecular assemblies depend on their assembled structures [21], Therefore, controlling the structures of molecular assemblies with external stimuli leads to the development of stimuli-responsive luminescent materials. Recently, some photoluminescent materials showing stimuli-responsive properties have been reported [11, 21-34]. However, the number of stimuli-responsive photoluminescent liquid crystals is still limited [11, 21, 28-34], Here we focus on mechano- and thermochromic photoluminescent mesomorphic materials. As the first topic, we focus on LC materials that change their photoluminescent colors by mechanical and/or thermal stimuli. We then describe another... 

As mentioned in the introduction section, the photoluminescent properties of molecular assemblies depend on the assembled structures of photoluminescent moieties [11, 21-34]. If assembled structures of photoluminescent moieties are changed by external stimuli, stimuli-responsive photoluminescent materials can be prepared. Recently, we have reported on anthracene, pyrene and naphthalene derivatives 1-3 having dendritic moieties which contain amide moieties to form intermolecular hydrogen bonds (Fig. 2) [28-30]. These dendritic moieties are known to be... 

Inorganic SP chemistry is an important branch of chemistry that has been the subject of extensive research and has also been extensively reviewed (12-15). The development of new materials with specific properties is a major endeavor for chemical research. New catalysts, or superconductors, or photoluminescent materials, or fer-... 

Figure 11.3 Structure and synthesis of the photoluminescent materials discrete library L2.

In this chapter we have described the mesomorphic behavior and ionic conductivities of ionic liquid-based liquid crystalline materials. These ion-active anisotropic materials have great potentials for applications not only as electrolytes that anisotropically transport ions at the nanometer scale but also as ordered solvents for reactions. Ionic liquid crystals have also been studied for uses as diverse as nonliner optoelectronic materials [61, 62], photoluminescent materials [78], structuredirecting reagents for mesoporous materials [79, 80] and ordered solvents for organic reactions [47, 81]. Approaches to self-organization of ionic liquids may open a new avenue in the field of material science and supramolecular chemistry. 

On the other hand, in the excitation spectrum, the emission intensity 4, at the monitored emission band, is plotted as a function of the wavelength A of the excitation light, w hich varies as the extinction coefficient of the absorbing molecules. Therefore, the excitation spectrum exhibits the same spectral appearance as that of the absorption spectrum. The advantage of measuring the excitation spectrum in addition to the emission spectrum is the greater sensitivity even for low concentrations of photoluminescent material compared to standard absorption measurements. 

These biopolymers can be used for the immobilization of metal ions not only with the final objective of metal recovery (and subsequent valorization by desorption or chemical/thermal destmction of the polymer matrix) but also for elaborating new materials or designing new applications. Depending on the metal immobilized on the biopolymer, it is possible to design new sorbents (immobilization of iron on alginate [119], of molybdate on chitosan [59], for As(V) removal, of silver on chitosan for pesticide removal [120]), supports for affinity chromatography [121], antimicrobial material [122], drug release material [123], neutron capture therapy [124], and photoluminescent materials [125]. These are only a few... 

In Pig. I. I, wc have drawn schematically a crystal or a grain of a photoluminescent material in order to illustrate the delinition. Our system consists of a host lattice and a luminescent center, often called an activator. For example, consider the famous luminescent materials AljOj Cr (ruby) and YjOj Eu . The host lattices are AliOt and YiOj, the activators the Cr and the Eu ions. 

Photoluminescent materials in which luminescence output can be modified by interaction with a substrate are being extensively investigated for use as sensors. Luminescent Ir complexes have been used as oxygen sensors, homocysteine sensors, metal cation sensors, and volatile organic compound sensors because of their rich photophysical properties. 

Silicon-based materials with unique (opto)electronic properties photoluminescent materials for flat panel technology, displays, light-emitting diodes, sensors electroluminescence, nonmetallic conductors, e.g. siloles, polysilanes, 2,3-diphenyl-1-silacyclobutene chemistry design and application of liquid crystals. 

S. Destri, M. Pasini, W. Porzio, A. Gavezzotti and G. Filippini, X-ray diffraction studies and computer simulations of the crystal and molecular structure of 2,5-di-(9,9-dimethylfluoren-2-yl)-3,4-dihexyl-thiophene-l,1-dioxide, a photoluminescent material, Cryst. Growth Des., 3, 257 - 262 (2003). 

Meyer J, Tappe F (2014) Photoluminescent materials for solid-state lighting state of art and future challenges. Adv Opt Mater... 

We provide a literature survey of a number of classical techniques used to quantify the chemical composition of porous silicon, highlighting their general merits and potential limitations with the material. Much of the early literature was focused on photoluminescent material, but increasingly there are studies on nanocomposites where chemical composition analysis is required to assess the degree and uniformity of impregnation or surface attachment. 

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