Luminescent powders

Fig. 6.1. Cross section of a low-pressure luminescent lamp. / glass tube 2 luminescent powder 3 cathode 4 lamp cap...

M. A. Flores-Gonzales, G. Ledoux, S. Roux, K. Lebbou, P. Pierriat, O. Tillement, Preparing nanometer scaled Tb-doped Y203 luminescent powders by the polyol method, J. Solid State Chem., 178, 989-997 (2005). 

Davenport et al. (1952) were unsuccessful in their attempts to restore the luminescence of the filtered aqueous extract of Luminodesmus. Hastings and Davenport (1957) saw a weak luminescence in their filtered aqueous extracts made from the acetone powder of the millipedes. They found that the luminescence is dependent on pH, with an optimum at about pH 8.9, and that the light intensity could be increased by 10-30% by adding ATP. Hastings and Davenport also measured the luminescence spectrum of live animals, finding an emission peak at 495 nm. 

Fig. 10.S.3 Luminescence spectrum of the light emitted from freeze-dried, powdered specimens of the ascidian Clavelina miniata upon addition of water. The same luminescence spectrum was obtained when living specimens were stimulated. From Chiba et ai, 1998, with permission from John Wiley Sons Ltd.

Several solid surfaces, such as filter paper, sodium acetate, and silica gel chromatoplates with a polyacrylate binder, have been used in solid-surface luminescence work (1,2). Experimentally it is relatively easy to prepare samples for analysis. With filter paper, for example, a small volume of sample solution is spotted onto the surface, the filter paper is dried, and then the measurement is made. In many cases, an inert gas is passed over the surface during the measurement step to enhance the RTF signal. For powdered samples, the sample preparation procedure is somewhat more involved. Commercial instruments can be readily used to measure the luminescence signals, and a variety of research instruments have been developed to obtain the solid-surface luminescence data (1,2). 

The defects of the matrix play an important role on luminescent performances in these materials. Taking into consideration the preparation process of these compounds with the solid-state reaction of mixtures of BaC03, H3BO3, and NH4H2PO4 at different molar ratio, non-equal evaporation during the sintering process of these powders is inevitable and thus results in the formation of intrinsic defects, such as cation and oxygen vacancies. Positional disorder of B and Vacant B (Vb)" have been reported in SrBPOs crystals on the basis of... 

Therefore, there could exist rich defects in Ba3BP30i2, BaBPOs and Ba3BP07 powders. From the point of energy-band theory, these defects will create defect energy levels in the band gap. It can be suggested that the electrons and holes introduced by X-ray excitation in the host might be mobile and lead to transitions within the conduction band, acceptor levels, donor levels and valence band. Consequently, some X-ray-excited luminescence bands may come into being. 

X -Ray powder pattern studies of the complexes [M(phen)2X2]" and [M(bipy)2YZ]"+ [M = Co, Rh, Ir, or Os X = Cl, H2O, or ox YZ = CI2 or (0H)(H20)] show that each metal in each series is isomorphous. A cis configuration is therefore assigned to all complexes. Luminescence quantum yields have been measured for a series of [IrCl2(N—N)2C1 complexes (N—N = phen or bipy, or diphenyl derivatives), permitting a quantitative estimate of the effect of ligand phenyl substituents.A normal-co-ordinate analysis (i.r. has been carried out for [Ir(NH3)5Cl]Cl2. ... 

Spectroscopic properties of [Ru(bpy)3] " ", and the effects of varying the diimine ligands in [Ru(bpy)3 L ] + (L = diimine) on the electronic spectra and redox properties of these complexes have been reviewed. The properties of the optical emission and excitation spectra of [Ru(bpy)3] +, [Ru(bpy)2(bpy-d )] + and [Ru(bpy-d )3] " " and of related Os, Rh , and Pt and Os species have been analyzed and trends arising from changes in the metal d or MLCT character in the lowest triplet states have been discussed. A study of the interligand electron transfer and transition state dynamics in [Ru(bpy)3] " " has been carried out. The results of X-ray excited optical luminescence and XANES studies on a fine powder film of [Ru(bpy)3][C104]2 show that C and Ru localized excitation enhances the photoluminescence yield, but that of N does not. 

Spectroscopic analyses of solid-state reactions must first use solid-state techniques (IR, UV/Vis, Raman, luminescence, NMR, ESR, CD, X-ray powder diffraction, DSC, etc.) in order to secure the solid-state conversion, before the solution techniques (detection of minor side products, specific rotation, etc.) are applied. 

A big advantage of the solid-solid technique is the possibility of obtaining complexes that are not obtainable from solution. It must, however, be shown that uniform complexes rather than microcrystalline mixtures occur. Apart from X-ray powder diffraction (which does not properly account for very small crystallites), proof is obtained by solid-state spectroscopy (IR, UV, luminescence) or, in the case of stable radicals, by magnetic susceptibility measurements. The 1 1 and 2 1 complexes 68-72 were prepared by stoichiometric milling and relevant physical properties are collected in Table 3 [20]. 

The cathodoluminescence of thin films containing rare-earth oxides was studied by Hansen and Myers (140). Films of yttrium oxide doped with rare earths were prepared in vacuum by electron-bombardment evaporation of the oxide powder mixtures. Luminescent rise and decay curves were obtained for activation with europium, gadolinium, terbium, and dysprosium. 

It has been possible to derive J for several salts of [(en)2Cr(OH)2Cr(en)2]4+ from low-temperature single-crystal absorption and powder luminescence spectra in the region of the 4A2 A2— aA2E transition of the paired system.444 The difference of up to 10% from the values derived from powder magnetic susceptibility data indicates a slight temperature dependence of /. 

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