Rare Earth Ion Pairs Research Articles

Broad Band excited NIR emission in Li2CeO3:Nd/Yb phosphor for modification of solar spectrum

Abstract Luminescence in Li2CeO3 host has been investigated for the first time. Nd3+ and Yb3+ activators led to emission in the near infrared region. Excitation for 976 emission of Yb3+ is located in the near ultraviolet region in form of a broad band around 385 nm. Luminescence is attributed to the host sensitization, though the possibility of metal to metal charge transfer excitation is not ruled out. Additional characteristic lines were observed in the excitation spectrum for Nd3+ emission. Luminescence intensity of 976 emission almost doubled in Li2CeO3:Nd3+, Yb3+ phosphor owing to Nd3+→ Yb3+ energy transfer. Efficiency of Nd3+→Yb3+ energy transfer is about 87%. Absorption of near ultraviolet radiations followed by conversion to near infrared indicates the potential applications in solar photovoltaics. The phosphor is particularly attractive for such applications in view of the strong broad band excitation arising from allowed transitions, in contrast to majority of the phosphors reported in the literature based on rare earth ion pairs such as Tm3+-Yb3+ or Er3+-Nd3+ which involve narrow, weak, forbidden f-f transitions of activator ion.

Upconversion microparticles as time-resolved luminescent probes for multiphoton microscopy: desired signal extraction from the streaking effect

The great interest in upconversion nanoparticles exists due to their high efficiency under multiphoton excitation. However, when these particles are used in scanning microscopy, the upconversion luminescence causes a streaking effect due to the long lifetime. This article describes a method of upconversion microparticle luminescence lifetime determination with help of modified Lucy–Richardson deconvolution of laser scanning microscope (LSM) image obtained under near-IR excitation using nondescanned detectors. Determination of the upconversion luminescence intensity and the decay time of separate microparticles was done by intensity profile along the image fast scan axis approximation. We studied upconversion submicroparticles based on fluoride hosts doped with Yb3+-Er3+ and Yb3+-Tm3+ rare earth ion pairs, and the characteristic decay times were 0.1 to 1.5 ms. We also compared the results of LSM measurements with the photon counting method results; the spread of values was about 13% and was associated with the approximation error. Data obtained from live cells showed the possibility of distinguishing the position of upconversion submicroparticles inside and outside the cells by the difference of their lifetime. The proposed technique allows using the upconversion microparticles without shells as probes for the presence of OH? ions and CO2 molecules.

Selective Uptake of Rare Earths from Aqueous Solutions by EDTA-Functionalized Magnetic and Nonmagnetic Nanoparticles

Magnetic (Fe3O4) and nonmagnetic (SiO2 and TiO2) nanoparticles were decorated on their surface with N-[(3-trimethoxysilyl)propyl]ethylenediamine triacetic acid (TMS-EDTA). The aim was to investigate the influence of the substrate on the behavior of these immobilized metal coordinating groups. The nanoparticles functionalized with TMS-EDTA were used for the adsorption and separation of trivalent rare-earth ions from aqueous solutions. The general adsorption capacity of the nanoparticles was very high (100 to 400 mg/g) due to their large surface area. The heavy rare-earth ions are known to have a higher affinity for the coordinating groups than the light rare-earth ions but an additional difference in selectivity was observed between the different nanoparticles. The separation of pairs of rare-earth ions was found to be dependent on the substrate, namely the density of EDTA groups on the surface. The observation that sterical hindrance (or crowding) of immobilized ligands influences the selectivity could provide a new tool for the fine-tuning of the coordination ability of traditional chelating ligands.

Magnetic structure of endohedral fullerenes

The fullerene molecule, C60, has the capability to host a variety of atoms inside an icosahedral cage. Endohedrally doped fullerene structures are important to understand the behaviour of atoms with unfilled f shell. Electronic structure and magnetism of rare earth doped endohedral fullerenes with icosahedral symmetries are studied. A many body perturbation theory has been used to calculate the exchange interactions among the pairs of rare earth ions with two f-electrons. The ground multiplet of pairs is found to be non-magnetic. Possibilities of Raman transitions are also discussed. It is expected that the present approach will lead to an understanding of the magnetism of nano-materials.

Intrinsic optical bistability at atomic and molecular scale

A general model for intrinsic optical bistability is presented for atomic or molecular systems which can be decomposed into two weakly interacting subsystems. It is shown that optical bistability should occur when the interaction between the two subsystems fluctuates faster than the characteristic time of the interaction. The validity of the model is demonstrated in the case of magnetic bistability of conduction electrons. It is extended in the infrared or visible range with pairs of rare earth ions and rare earth-transition metal ions systems.

Spectroscopy of Ion Pairs in Binuclear Compounds; CsCdBr3:Pr3+

The spectroscopy of pairs of rare-earth ions is demonstrated for Pr3+ :CsCdBr3• For reasons of charge compensation only two definite types of Ρr3+ pairs are formed independent of concentration. Only the pair with the Pr3 + ions as direct neighbors shows upconversion. The dynamics of this upconversion process is studied by time-resolved spectroscopy and discussed in the energy leve1 schemes of the single ions, and the pair.

Empirical values for growth-induced anisotropy energy coefficient for designing garnet LPE films

Growth-induced anisotropy energy coefficients and their super-cooling temperature dependence, both attributed to rare-earth ion-pairs, K i j, and α i j, are obtained by analyzing the relationship between growth temperature dependence of uniaxial anisotropy energy, K u, and garnet compositions. Regression processes were used for analysis. Better agreements are obtained when the newly obtained K i j and α i j values are applied to estimate growth-induced anisotropy energy for 24 garnet compositions. The ratio of calculated growth-induced anisotropy energy values to observed values is 0.98 ± 0.12, when newly obtained K i j and α i j values are used in place of Eschenfelder's K i j values (0.85 ± 0.24). Appropriate melt compositions, to obtain LPE garnet films with bubble properties which meet device requirements, are easily given by computer simulation using the newly obtained values.

Interactions between rare earth ions in the ethyl sulphates

The existing data on the interactions between a large number of different pairs of rare earth ions in ethyl sulphates is surveyed as a whole, and some comparisons are made with similar data for LaCl3 and LaBr3. Such an analysis of all of the data enables one to draw much firmer conclusions about the interaction mechanisms than a discussion of the results for any particular pair of ions. It is shown that exchange contributes very little to the interaction, and that electric multipole-multipole interaction contributions are negligible. This suggests that the sizeable nondipolar contribution to the interaction should be attributed to virtual phonon exchange (VPE). Estimates of this interaction based upon standard theories show that the interaction must be enhanced by a factor of 40-50 in order to agree with the experimental measurements. That this enhancement factor remarkably consistent for all of the data, and that one can invent a plausible model to account for the enhancement factor in terms of contributions from optical phonon modes, indicates that VPE interaction is the appropriate mechanism.

Observation of simultaneous electronic transitions for rare-earth ion pairs in aqueous solution

In concentrated aqueous solutions at 298°K absorption bands observed for praseodymium ion at 24 154, 24 844, and 25 974 cm −1 are assigned as simultaneous transitions for Pr 3+ ion pairs to states[ 3P 0][ 3H 6], [ 3P 0][ 3F 2], and [ 3P 0][ 3F 3] from the pair ground state [ 3H 4][ 3H 4]. A shoulder at 23 200 and a band at 27 400 cm −1 are assigned analogously. The interpretations and applications of simultaneous transitions in metal-ion pairs in solution are discussed.