Fundamental informations concerning the electronic structure of high-lying levels of rare earth ions as well as the mechanisms of energy transfer from the host lattice to the activator and the processes of electronic excitation multiplication were obtained for a series of fluoride matrices doped with trivalent rare earth ions as luminescence activators, using synchrotron facilities. Lifetime measurements of the radiatively decaying levels of the emission centre provide information on the kinetics of the energy transfer.

VUV emission of several stoichiometric fluoride crystals containing Er3+ and Tm3+ ions (LiErF4, LiTmF4, KErF4, KTmF4, BaTm2F8) has been studied with the technique of time-resolved spectroscopy under the pulsed synchrotron radiation excitation. Both fast (nanosecond) and slow (microsecond) VUV emission was detected for Tm3+-containing compounds in the studied spectral range (150–200 nm) while for Er3+-containing crystals only fast emission is observed. The difference is due to different energy level schemes for high-lying 4f states of these ions. In case of Er3+ the energy position of some high-lying 4f states is very close to that of emitting 5d levels and so the concentration quenching leads to considerable shortening of the emission.

Abstract— The first overview of the 4f levels of Gd3+ in the VUV is reported. It is shown that quantum cutting is a very promising phenomenon to make VUV phosphors with a quantum efficiency greater than 100% and that the efficiency of this process can be improved by cross‐relaxation. The visible quantum efficiency of LiGdF4: Eu3+ 0.5 mol% upon excitation in the VUV is shown to be 195%.

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The VUV emission of several wide bandgap crystals (BaY2F8, LiYF4, SrF2, BaF2) doped with Er3+ and Tm3+, stoichiometric ErF3 and TmF3, and (YPO4, LuPO4) doped with Nd3+, has been studied using time-resolved spectroscopy under pulsed synchrotron radiation excitation. For Nd3+, only fast (nanosecond) VUV emission due to allowed 4f25d→4f3 interconfiguration transitions is observed in the studied spectral range (150–200nm), while for Er3+ and Tm3+ both fast and slow (microsecond) emissions were detected. The efficiency of energy transfer from the matrix to the rare earth ion is very low in all fluoride crystals studied, while in YPO4 and LuPO4 doped with Nd3+ a very efficient energy transfer mechanism exists leading to a high quantum yield of the VUV emission for these compounds. On high-energy excitation the decay kinetics of the 5d→4f emission become non-exponential and both the acceleration and delay of the decay can be observed for the particular material.

As far as luminescence applications are considered, large band gap materials are the most suitable hosts which permit by incorporating a small concentration of foreign Ions (activators) into the lattices, to obtain emission of visible photons in a large energy domain. Such frequency converters are usually called phosphors.

VUV emission of several fluoride crystals doped with Er3+ and Tm3+ has been studied under pulsed synchrotron radiation excitation. It was shown that emission spectra of these ions in the 150–190 nm spectral range consist of both fast emission bands (decay constant in the range from a few to tens of nanoseconds) and slow ones (decay constant in the microsecond range). A model is proposed which explains the co-existence of the slow and fast components by the competition of the parity-allowed interconfiguration 4fn−15d → 4fn radiative transitions (fast emission) and parity-forbidden intraconfiguration 4fn → 4fn transitions (slow emission). Depending on the relative position of corresponding emitting levels both fast and slow emissions, or only slow, or only fast emission are observed.

Decay kinetics of 4f25d state of Nd3+ is very fast (τ ~ 1 ns) in NdF3 where concentration quenching of Nd3+ emission is observed. It is near-exponential in YF3-Nd, where relatively weak quenching of emission takes place at high-energy excitation. It shows distinct rise time in LiYF4-Nd where the delayed energy transfer to emission centers is observed. The latter starts at excitation energies higher than the energy of intrinsic absorption edge of the matrix and disappears at low temperature. The model for the mechanism of the delayed energy transfer in LiYF4-Nd is proposed.

From the point of view of luminescence applications, large band gap materials such as fluoride compounds are suitable matrices into which a small concentration of foreign ions called activators can be incorporated. To improve the knowledge of the optical properties of the overall system, the investigation of the different interactions of UV and VUV electromagnetic radiations with the condensed matter was undertaken. The excitation of the luminescence induced in rare earth ion activators doped in LiYF4, LaF3 and YF3 was recorded in a wide continuous spectral region from 5 to 15 eV using synchrotron radiation as a photon source. The main interest of this work was focused on the localization in energy of the different photon absorption mechanisms occurring in these fluoride compounds doped with rare earth ions.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.