The rare earth elements (REEs) form a chemically uniform group and include yttrium (Y), lanthanum (La) and the lanthanides cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu) Their average abundance in the Earth’s crust range from 66µg g−1 in Ce to 05µg g−1 in Tm and «01µg g−1 in Pm Recent great improvements in more routine analytical technique, the use of REEs as fertilisers, at least in East Asian agriculture, and the importance of these elements as indicators in both pedological and physiological processes and reactions have contributed to an increased interest in these previously less considered elements in environmental sciences This review of recent and current literature deals with REEs in primary and secondary soil minerals, concentrations in surface soils, factors influencing adsorption, solubility and transport in soils, including weathering and transformations of REE minerals, and vertical distribution in soil profiles Reviewed and discussed are also concentrations, distribution and localisation of REEs in plants and plant organs, soil-plant relationships and interactions, effects on plant growth and crop production and their importance in plant physiology and biochemistry The REEs are found, usually several elements together, as phosphates, carbonates and silicate minerals finely dispersed especially in magmatic and metamorphic rocks REE concentrations in surface soils of humid climates, such as the A(E)-horizons of Podzols and Laterites, are usually lower than in the parent material, due to higher weathering and leaching rates than of the average soil constituents Some fractionation may occur due to the formation of more element-specific secondary minerals Transfer from soil to plant is usually low, but extreme accumulators are found, eg, among several species of ferns Roots have generally higher concentrations than shoots Possible uptakemechanisms of REEs are discussed Uptake is positively, though often weakly, correlated with soil acidity and easily soluble concentrations of the elements, but rarely well related to their total concentrations in the soil Under certain conditions, low concentrations of at least some REEs seem to favour plant growth and productivity, but the physiological mechanisms are still not well understood Some considerations concerning the boundary between essential and non-essential micro nutrients are discussed

Rare earth elements in soil and plant systems - A review

The optical properties of five different nanocrystalline Y2O3:Er3+, Yb3+ samples are presented and discussed. Green and red emission was observed following excitation with 488 nm and attributed to 2H11/2, 4S3/2→4I15/2, and 4F9/2→4I15/2 transitions, respectively. Striking red enhancement was observed in the upconversion spectra when exciting the Y2O3:Er3+, Yb3+ samples with 978 nm, and it became more pronounced with an increase in Yb3+ concentration. A cross relaxation mechanism (4F7/2→4F9/2 and 4F9/2←4I11/2) was responsible for directly populating the 4F9/2 state but did not explain the difference in the magnitude of red enhancement between identically doped bulk and nanocrystalline Y2O3:Er3+, Yb3+ samples. The 4F9/2 level was populated via a nonresonant mechanism that involved the 4F9/2←4I13/2 transition that is more prevalent in the nanocrystals, which is due to the high energy phonons inherent in this type of material. In nanocrystalline Y2O3:Er3+, Yb3+, we observe a change in the upconversion mechanis...

Significance of Yb3+ concentration on the upconversion mechanisms in codoped Y2O3:Er3+, Yb3+ nanocrystals

Nanocrystalline calcium phosphate ceramics in biomedical engineering

Colloidal solutions and redispersible powders of nanocrystalline, lanthanide-doped YVO4 have been prepared via a hydrothermal method at 200 °C. High-resolution transmission electron micrographs of size-selected samples show highly crystalline particles ranging in size from about 10 to 30 nm. The particles exhibit the tetragonal zircon structure known for bulk material. Upon UV excitation of the vanadate host, the energy is transferred to the lanthanide ion and strong luminescence (f−f transitions) is observed. By analyzing line splitting and intensity pattern in the luminescence spectrum of the europium-doped sample, we are able to verify that the dopant ions enter the same lattice site as in bulk material despite the nanocrystalline nature of the sample and the low-temperature synthesis. For YVO4:Eu nanoparticles a luminescence quantum yield of 15% at room-temperature was observed.

Wet-chemical synthesis of doped colloidal nanoparticles : yvo4:ln (ln = eu, sm, dy)

A simple hydrothermal method has been developed for the systematic synthesis of lanthanide orthophosphate crystals with different crystalline phases and morphologies. It has been shown that pure LnPO4 compounds change structure with decreasing Ln ionic radius:  i.e., the orthophosphates from Ho to Lu as well as Y exist only in the tetragonal zircon (xenotime) structure, while the orthophosphates from La to Dy exist in the hexagonal structure under hydrothermal treatment. The obtained hexagonal structured lanthanide orthophosphate LnPO4 (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy) products have a wirelike morphology. In contrast, tetragonal LnPO4 (Ln = Ho, Er, Tm, Yb, Lu, Y) samples prepared under the same experimental conditions consist of nanoparticles. The obtained hexagonal LnPO4 (Ln = La → Tb) can convert to the monoclinic monazite structured products, and their morphologies remained the same after calcination at 900 °C in air (Hexagonal DyPO4 is an exceptional case, it transformed to tetragonal DyPO...

Systematic synthesis and characterization of single-crystal lanthanide orthophosphate nanowires.

Combustion synthesis and photoluminescence of nanocrystalline Y2O3:Eu phosphors

The distribution pattern of La, Ce, Nd, Tb, Dy was in the order as leafrootstem, that of Pr, Sm, Eu, Gd, Ho, Y was as rootleafstem in fern Dicranopteris dichotoma Underw. Light and moderately heavy rare earth elements were easily selectively absorbed and then accumulated by the fern D. dichotoma . Many mainly light rare earth elements are bound to chlorophyll in D. dichotoma . Among the 15 detectable rare earth elements binding to chlorophyll, lanthanum content (50.08%) was the highest, and cerium content (19.40%) is the second of all. FXAFS (Fluorescence X_ray absorption fine structure) spectral analysis revealed that lanthanum coordinated 2 porphyrin rings and La_chlorophyll_a may have bilayer structure in D. dichotoma.

Distribution of rare earth elements and structure characterization of chlorophyll-lanthanum in a natural plant fern Dicranopteris dichotoma

Elemental analysis indicated that La-chlorophyll-a and Sm-chlorophyll-a have the double decker sandwich structure, Cu-chlorophyll-a has the mono decker structure

Tao Ye

Papers

Combustion synthesis and photoluminescence of nanocrystalline Y2O3:Eu phosphors

Distribution of rare earth elements and structure characterization of chlorophyll-lanthanum in a natural plant fern Dicranopteris dichotoma

Determination of coordination structure on metal-substituted chlorophyll a by spectroscopy

Combustion synthesis and photoluminescence of nanocrystalline Y{sub 2}O{sub 3}:Eu phosphors

Distribution, accumulation and transportation of rare earth elements in soil-Dicranopteris linearis system at South Jiangxi