Lanthanide phosphors

Colour televisions and similar displays are the largest commercial market for lanthanide phosphors, with over 100 million tubes manufactured a year. About 2 g of phosphor is used in each tube. The lanthanide involvement in a traditional colour TV tube works along these... 

In general low symmetry cation sites produce the most intensely emitting lanthanide phosphors. 

Inorganic phosphors are potential labels for time-resolved luminescence staining and assays in aqueous environment [23, 52-55]. The lanthanide phosphors have essentially infinite shelf life, no toxicity, no photobleaching, and are unaffected by environmental conditions such as pH, temperature, enzymatic reactions, or solvent effects. Their major drawback is that the luminescence per lanthanide ion is significantly less than from the dye-doped or dye nanoparticles due to the weak absorption of individual ions partly compensated by their higher number. Inorganic nanoparticles, however, can be prepared readily in large quantities with relatively simple methods. The size of the nanoparticles can be controlled from low nanometer scale to several hundred nanometers with a narrow size distribution. 

Soukka T, Kuningas K, Rantanen T et al (2005) Photochemical characterization of up-converting inorganic lanthanide phosphors as potential labels. J Fluoresc 15 513-528... 

Up to now, some basic applications have been presented which apply in some cases to lanthanide complexes and in other cases to lanthanide phosphors or inorganic... 

The screen materials are made from a variety of heavy metals compounds such as oxides, sulfides, aluminates or silicates of metals such as zinc, cadmium and ffingsten. More efficient phosphors use lanthanides. The materials are usually activated by dopants such as silver, copper and europium. These allow fine-ffining of the emitted wavelengths and optimisation of the efficiency of the materials. Typical materials are M2O2S where M is Gd or La, doped, for example, with Tb, Eu, or Pr, or Y3(Al,Ga)50i2 doped with Ce or Tb (see Chap. 4 for more information on solid-state lanthanide phosphors). 

Group III with electronic configuration 5s 4d . The principal ore is gadolinite (a silicate also containing lanthanides). Y2O3 containing Eu is used as a red phosphor in colour television. Yttrium iron garnets are used as microwave filters. 

Lanthanide luminescence apphcations have already reached industrial levels of consumption. Additionally, the strongly specific nature of the rare-earths energy emissions has also led to extensive work in several areas such as photostimulable phosphors, lasers (qv), dosimetry, and fluorescent immunoassay (qv) (33). 

The role of cerium in these lighting phosphors is not as the emitting atom but rather as the sensitizer. The initial step in the lighting process is the efficient absorption of the 254 nm emission Ce ", with broad absorption bands in the uv, is very suitable. This absorbed energy is then transferred to the sublattice within the crystalline phosphor eventually the activator ion is fed and emission results. Cerium, as a sensitizer ion, is compatible in crystal lattices with other lanthanide ions, such as Eu and Tb, the usual activator atoms. 

Current availability of individual lanthanides (plus Y and La) in a state of high purity and relatively low cost has stimulated research into potential new applications. These are mainly in the field of solid state chemistry and include solid oxide fuel cells, new phosphors and perhaps most significantly high temperature superconductors... 

Figure 2 Structures of some lanthanide complex phosphors (a) [Eu(TTFA)3(phen)], (b) [Tb(ACAC)3 (phen)], (c) [Dy(BTFA)3(phen)], (d) [Eu(DBM)3(phen)], (e) [Eu(DBM)3(bath)] and (f) [Eu(TTFA)3(TPPO)2]...

Lanthanide-doped inverse photonic crystals have been reported.282 The lattices were prepared by infilling self-assembled polystyrene sphere templates with a mixture of zirconium alkoxide and europium at 450 °C, the polystyrene spheres were burnt out leaving hollow spheres of air, and the infilled material was converted to Zr02 Eu3+. The PL properties of the resulting photonic lattice were reported.282 The possibility of including phosphors into photonic lattices could lead to many... 

This comparison of the spectroscopic properties of the different types of fluorescent reporters underlines that semiconductor QDs and upconverting nanoparticles have no analogs in the field of organic dyes. Therefore, their unique features are unrivaled. The different molecular labels detailed here each display unique advantages that can compete with some of the favorable features of QDs and upconverting phosphors such as long lifetimes in the case of MLC systems and lanthanide chelates or very narrow emission bands for lanthanide chelates beneficial for spectral multiplexing. 

The rare earth (RE) ions most commonly used for applications as phosphors, lasers, and amplifiers are the so-called lanthanide ions. Lanthanide ions are formed by ionization of a nnmber of atoms located in periodic table after lanthanum from the cerium atom (atomic number 58), which has an onter electronic configuration 5s 5p 5d 4f 6s, to the ytterbium atom (atomic number 70), with an outer electronic configuration 5s 5p 4f " 6s. These atoms are nsnally incorporated in crystals as divalent or trivalent cations. In trivalent ions 5d, 6s, and some 4f electrons are removed and so (RE) + ions deal with transitions between electronic energy sublevels of the 4f" electroiuc configuration. Divalent lanthanide ions contain one more f electron (for instance, the Eu + ion has the same electronic configuration as the Gd + ion, the next element in the periodic table) but, at variance with trivalent ions, they tand use to show f d interconfigurational optical transitions. This aspect leads to quite different spectroscopic properties between divalent and trivalent ions, and so we will discuss them separately. 

Suppose that you are going to develop an ultraviolet-emitting phosphor based on a trivalent lanthanide rare earth ion doped crystal. If you want this phosphor... 

Table 4.17 Comparison of the Extraction Constants Aei for the Ilh-Suhgroup Divalent Ions, and inh Lanthanide Ions, with Sulfur or Oxygen Dialkyl Phosphoric Acids ...

Lanthanides are also found as minor components in other ores, particularly in association with uranium or in phosphate rock. These are often coextracted with the major product and can be economically recovered from the waste streams resulting from the uranium or phosphoric acid extraction. 

Chemically pure reagents were used. Cadmium was added as its sulfate salt in concentrations of about 50 ppm. Lanthanides were added as nitrates. For the experiments with other metal ions so-called "black acid from a Nissan-H process was used. In this acid a large number of metal ions were present. To achieve calcium sulfate precipitation two solutions, one consisting of calcium phosphate in phosphoric acid and the other of a phosphoric acid/sulfuric acid mixture, were fed simultaneously in the 1 liter MSMPR crystallizer. The power input by the turbine stirrer was 1 kW/m. The solid content was about 10%. Each experiment was conducted for at least 8 residence times to obtain a steady state. During the experiments lic iid and solid samples were taken for analysis by ICP (Inductively Coupled Plasma spectrometry, based on atomic emission) and/or INAA (Instrumental Neutron Activation Analysis). The solid samples were washed with saturated gypsum solution (3x) and with acetone (3x), and subsequently dried at 30 C. The details of the continuous crystallization experiments are given in ref. [5]. 

General, in order to precipitate either AH, HH or DH the appropriate temperature and phosphate and/or sulfate concentration must be selected. In table 2 the operational conditions are listed for each experiment. In the experiments where DH is crystallized only the sulfuric acid concentration, the temperature and the residence time were varied. In case of HH crystallization various sulfuric acid and phosphoric acid concentrations were applied. AH crystallization has been studied at various residence times, in the presence of lanthanides or AIF3 and also in black acid from a Nissan-H process. 

Berthod et al. [325] employed countercurrent chromatography with diethyl-hexyl phosphoric acid (DEHPA) reverse micelles in heptane as a stationary phase to extract metaUic cations such as Fa +, Ce, Pr, and Nd + (lanthanide series). This technique was suggested for the application of ion filtering and concentration or for deionization of aqueous phases. Ashrafizadeh et al. [326] re-... 

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