Chapter 11 Flashcards
1
Q
- What are MRI contrast agents? What are the requirements for a good MRI contrast agent?
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2
Q
- Work out the ground states for Pm3+, Eu3+, Er3+, Pr4+, Eu2+.
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3
Q
- A solution of Eu(ClO4)3 in water shows a weak luminescence upon irradiation with light of a wavelength of 393 nm. Upon addition of the sodium salt of pyridine-2,6-dicarboxylic acid (dipicolinic acid), a steady increase of the luminescence intensity is observed until the metal-to-ligand ratio is 1:3. Further addition of the ligand does not appreciably change the luminescence output. However, the luminescence becomes much stronger upon changing the excitation wavelength from 393 nm to 266 nm. Explain these observations.
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4
Q
- (a) Why do La3+, Lu3+ and Gd3+ compounds not show visible luminescence? (b) Explain why f–f transitions in the electronic spectra of lanthanide complexes are weaker than d–d transitions in the corresponding spectra of transition metal complexes. (c) What are hypersensitive transitions? (d) Why should water molecules be avoided in the first coordination sphere of luminescent lanthanide complexes?
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5
Q
- What is the mechanism of sensitized lanthanide luminescence? Use a scheme to illustrate this mechanism.
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6
Q
- Describe the application of rare earths in lamp phosphors (working principle of fluorescent lamps, types of phosphors used, mechanism of sensitized luminescence in lamp phosphors).
- Why is Y2O3Eu3+ an excellent red phosphor for fluorescent lamps? Why do green lamp phosphors obtain contain Ce3+ or Gd3+ besides the Tb3+ ion?
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7
Q
- Explain the working principle of a four-level neodymium laser.
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8
Q
- Describe the hysteresis loop of a ferromagnetic material.
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9
Q
- Compare the advantages and disadvantages of neodymium-iron-boron and samarium-cobalt magnets.
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10
Q
- Discuss the effect direct substitution of Nd by Dy in NdFeB alloys on the magnetic properties of neodymium-iron-boron magnets. How can the amount of Dy in NdFeB alloys be minimised?
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