Trivalent thulium

Johnson et al. (55) have reported a phonon-assisted energy exchange from trivalent erbium to trivalent thulium or to trivalent holmium. In this case, these authors were able to rule out resonance exchange completely Of some importance is that these systems are useful for laser oscillators, and the energy exchange results in a substantial decrease in threshold. 

In the case of thulium compounds TmSe and TmTe and YI3AI3, distinct multiplet structures due to divalent and trivalent thulium are seen in the 4f region [38]. The multiplet structure in TmTe is more distinct than in the case of TmSe in agreement with magnetic susceptibility data, (i.e.) magnetic moment of TmTe is smaller than that of TmSe. 

In 1961 Hayes and Twidell (8) found that if calcium fluoride crystals containing trivalent thulium were irradiated with x-rays, some of the thulium was converted to the divalent state. This discovery was the first of many in the study of dilute solutions of divalent rare earth ions. Most workers prefer to study the alkaline earth fluorides since these materials are stable with respect to air and have more attractive mechanical properties than the alkaline earth chlorides, bromides, and iodides. Enough work has been carried out in these softer materials to show that reactions similar to those in the fluorides do occur. 

The energy of the lowest Coulomb transition in trivalent thulium, the Hg— F4 transition, is at just under 700 meV with transitions to the... 

The incorporation of metallic NPs in RE-doped glasses has been intensively investigated in recent years for its positive effects on the PL behaviors of RE ions. Among various RE ions, the trivalent thulium ion exhibits rich emissions from visible bands to the mid-lR region, and its absorption band for the H4 state at 0.8 pm facilitates the use of the commercial GaAlAs diode laser as a pump source. In the present work, the NIR PL spectra of the Tm -doped 70GeS2-... 

Bivalence is similarly shown for europium, and trivalence for the elements gadolinium to thulium. 

Although rare-earth ions are mosdy trivalent, lanthanides can exist in the divalent or tetravalent state when the electronic configuration is dose to the stable empty, half-filled, or completely filled shells. Thus samarium, europium, thulium, and ytterbium can exist as divalent cations in certain environments. On the other hand, tetravalent cerium, praseodymium, and terbium are found, even as oxides where trivalent and tetravalent states often coexist. The stabilization of the different valence states for particular rare earths is sometimes used for separation from the other trivalent lanthanides. The chemicals properties of the di- and tetravalent ions are significantly different. 

The absorption and emission spectra of thulium and erbium were studied in phosphate and borate glass by Reisfeld and Eckstein (31, 32). Their objectives were 1) to study the influence of two different glass hosts on the transition probabilities of trivalent Er and Tm ions (henceforth R.E.), 2) to compare the intensities of the spectra of these R. E. in glcisses with those of liquid solutions and doped oxide lattices, and 3) to compare the broadening of the R. E. fluorescence bands in glasses with those in aqueous solutions and doped crystals. 

Thulium (Tm) is a unique heavy lanthanide element. It is the last heavy lanthanide with an incomplete 4f shell. In the lanthanide series, thuhum is followed by ytterbium, which has a divalent electronic character and does not show the typical structural changes observed in other trivalent lanthanide elements. And the last element in the lanthanide series lutetium also has a completely filled 4f shell, and therefore is not expected to exhibit low symmetry structures at ultra high pressures. 

The high-temperature polymorphic form for most of the rare earth metals just before melting is the bcc structure. Four of the trivalent lanthanides (holmium, erbium, thulium and lutetium) are monomorphic and do not form a bcc structure before melting at atmospheric pressure (see fig. 4). However, the bcc phase can be formed in holmium and erbium by the application of pressure (< 1 GPa), see section 3.7.1. The existence of the bcc phase in the lanthanides has been correlated with the d occupation number, which decreases along the lanthanide series, but increases... 

Similar observations can be obtained for the thulium chalcogenides. TmTe is obviously divalent. With increasing internal pressure (decreasing lattice constant), the tendency towards trivalency increases. This means that TmS is purely trivalent and TmSe is mixed valent as is evident from the magnitude of their lattice constants. One of the first intermediate valent system studied by photoemission was the... 

Charge transfer bands result whenever an easily oxidized ligand is bound to a trivalent lanthanide ion which can be reduced to the divalent state or when the ligand is bound to one of the tetravalent ions (J0rgensen, 1970). Such transitions are commonly observed in the spectra of complexes of samarium(III), euro-pium(III), thulium(III), ytterbium(III), and cerium(IV). The position of these bands in the spectrum is markedly dependent on the ligand and the metal ion. For example, in the ions RCU the charge transfer bands for europium(III),... 

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