Thulium-169, excitation

In 2000, most European countries switched from their traditional currencies to the euro. Lanthanide luminescence is used as a means of preventing counterfeit euro banknotes from passing into the money chain. Excitation of euro banknotes with ultraviolet light results in fluorescence in the red, green and blue regions due to complexes of europium (Eu3+), terbium (Tb3+) and thulium (Tm3+), respectively, that are present in the banknotes. 

Thulium displays in minerals an intense UV and blue visible luminescence with a line spectrum near 360 and 450 nm, correspondingly. They are connected with electron transitions from different excited levels D2 and at 360-365 and 450-455 nm. The liuninescence of Tm " is more easily detected in time-resolved spectra with a narrow gate, because it usually has a relatively short decay time. The UV Hne usually has a much shorter decay time compared with the blue line. Different decay times from these levels are evidently connected with nonradiative relaxation due to the presence of high frequency vibrations in the lattice. The best excitation is at 355 nm, which is connected with transition... 

The thulium (III) ion exhibits spectrally narrow light emission at about 480 nm. Li and coworkers were the first to use the Tm + ion in OLEDs [65]. They prepared a Tm complex Tm(acac)3(phen) and constructed double-layer cells with structure ITO/PVK/Tm complex/Al. The electroluminescence spectrum of the OLED with drive voltage 10 V and the photoluminescence spectrum with excitation wavelength at 350 nm are shown in Figure 11.29. The emitting intensity of 6.0cdm was achieved when a 16 V forward bias voltage was applied. 

Figure 11.29 Square symbols-the EL spectrum of the device ITO/PVK/Tmcomplex/Al at drive voltage 10 V solid line - the PL spectrum of the Tm(ACAC)3(phen) powder (excitation wavelength 350 nm) [65]. (Reproduced from Synthetic Metals, 104, Z.R. Hong et al., Spectrally-narrow blue light-emitting organic electroluminescent devices utihzing thulium complexes, 165-168, 1999, with permission from Elsevier.)...

Thulium. Stimulated emission has been obtained from three states of Tm3+ 3H4,3, and Dp. Other excited states having high quantum efficiency in most hosts include 4 and 116... 

Fig. 1. Energy levels of trivaient lanthanides below 43000 cm (5.3 eV) arranged according to the number q of 4f electrons. Excited levels known frequently to luminesce are indicated by a black triangle. The excited levels corresponding to hypersensitive transitions from the ground state are marked with a square. For each lanthanide, J is given to the right (in the notation of atomic spectroscopy, ] is added to the Russell-Saunders terms as lower-right subscripts). When the quantum numbers S and L are reasonably well-defined, the terms are indicated to the left. It may be noted that the assignments and F< in thulium(lll) previously were inverted these two levels with 7 = 4 actually have above 60% of H and F character, respectively. Calculated 7-levels are shown as dotted lines. They are taken from Carnall et al. (1968) who also contributed decisively to the identification of numerous observed levels, mainly by using the Judd-Ofelt parametrization of band intensities.

Fig. 5 NIR photoluminescence excitation (dashed line, emission monitored at 800 nm) and emission spectra (solid line, excitation at 380 nm) of a thulium(III) complex (10 M in acetonitrile). Data adapted from [36]...

The effectiveness of the relaxation processes with thermal excitations of electronic states of the matrix ions diminishes as 6xp(-A/A b7 ) with the decrease of temperature. At fairly low temperatures the mechanism of nuclear relaxation via impurity paramagnetic centers, common for dielectrics, comes into effect (Abragam 1961, Khutsishvili 1968, Atsarkin 1980). This is well illustrated in fig. 20 the temperature motion of the nuclear relaxation rate is sharply slowed down for F at T < 5 K and fbr Tm at T < 3 K, and at the lowest temperatures the thulium nuclear moments relax only ten times faster than those of fluorine. This fact clearly shows that the relaxation of different nuclei proceeds by a single channel. The observed factor-of-ten difference is easily obtained, if one multiplies the concentration ratio nxm/nF = 4 by the ratio of the squares of their magnetic moments Thus, the role of 4f electrons is reduced here to the enhancement of dipole-dipole interactions of nuclei of the VV ions with impurity paramagnetic centers. 

The relaxation mechanism, connected with the random thermal excitation of the host lanthanide ions in VV paramagnets, proves to be effective for impurity ions too. We list the results of the relaxation rate measurements for a number of impurity lanthanide ions in TmES and LiTmF4 crystals (Aminov et al. 1986, 1989) (table 18). As for other investigations in this field, we may refer only to papers by Rimai and Bierig (1964), Rachford and Huang (1971), and Antipin et al. (1979) and only in the first of these papers was the influence of thuliiun ions on spin-lattice relaxation of Fe ions in thulium garnets observed with certainty. 

Multiplex detection using UPT was performed by Corstjens et al. [36] for the simultaneous detection of human antibodies against human immunodeficiency virus, Myobacterium tuberculosis and hepatitis C virus by using different antibodies adsorbed on adjacent test lines and one type of UCNPs. Hampl et al. [38] used two different types of particles (a thulium oxysulfide phosphor with blue emission and an erbium oxysulfide phosphor with green emission, both after being excited at 980 nm) for simultaneous detection of mouse IgG and ovalbumin. 

Besides triplet-triplet annihilation, a further process for achieving upconversion luminescence emission under continuous wave low-energy irradiation is based oti the use of lanthanide ions, most often erbium, holmium, and thulium (III) cations. In particular, a large variety of phosphors based on an inorganic host doped by lanthanide cations have been developed. The abundance of available states in these cations opens a large variety of paths for upconversion. As an example (Scheme 7.6), upconversion nanoparticles codoped with ytterbium and erbium cations exhibit a green emission due to the transitions from Hn/2 and respectively " Sn/2 excited states to the ground state as well as a red emission from the F9/2 state [10]. 

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