C. Parent

Luminescent properties of delafossite-type oxides LaCuO2 and YCuO2

Abstract Investigation of luminescent properties of delafossite-type CuLaO 2 and CuYO 2 oxides shows two emission bands resulting from two separated excitation bands: the emission band of lower energy results from the excitation to highest energy, exhibiting thus a larger Stokes shift. The existence of a single site for Cu + ions suggests a simple model involving two emitting levels: one corresponding to a 3 d 9 4 s 1 configuration and the other to a 3 d 9 4 p x , y 1 configuration.

Silver aggregates in photoluminescent phosphate glasses of the `Ag2O–ZnO–P2O5' system

Abstract Photoluminescent properties of glasses of the Ag 2 O–ZnO–P 2 O 5 system are reported. The compositions of the glasses are limited by the polyphosphate and diphosphate domain of this system. The phosphate structural units of the network former are deduced from Raman spectra. A comparison with the luminescent properties of crystallized silver phosphates of similar composition allows identification of two different emitting centers: isolated Ag + , Ag + –Ag + pairs, and a third center resulting from an Ag + –Zn 2+ interaction. The introduction of 1 mol% SiO 2 or Al 2 O 3 in these glasses leads to precipitation of silver particles, whose dimensions range from nanometers to micrometers, and to the appearance of luminescent centers (Ag 2 ) + detected around the micrometer particles by optical microscopy. We assume that these centers are an intermediate stage during the process of silver precipitation.

A structural interpretation of the Pb2+, Eu3+ and Nd3+ optical spectra in doped sodium borate glasses

Abstract The study of sodium borate glasses over the compositional range 10–35 mol.% Na2O by using Pb2+, Eu3+ and Nd3+ as local sounds shows the existence of two possible situations depending on whether the Na2O content is lower or higher than about 25 mol.%. In the first composition range the simultaneous increase of optical basicity and of modifier ion site asymmetry implies rather a 2D-character of the network former. The properties of the glasses with high Na2O content involve more 3D-character for the former sublattice.

Spectroscopic investigation of the copper (I)-rich phosphate CuZr2(PO4)3

The Nasicon-type phosphate CuZr2(PO4)3 exhibits two fluorescences occurring in the violet and green regions. They are assigned to two different centres: the violet one to isolated Cu+ and the green one to Cu+-Cu+ pairs occupying the same site. These assignments are in agreement with previous structural investigations using X-ray, neutron and EXAFS measurements and provide information about the location of copper ions in the crystal. A third luminescence is detected in the blue range at low temperature. The origin of this fast strong emission is not clearly established. It could be due to Cu+-Cu0 pairs in the M(1) site.

Energy transfer in a Nd3+-Yb3+ borate glass

Abstract The glasses investigated in the present study had the composition 15Li2O-10BaO-(5-x-y)La2O3-xNd2O3-yYb2O3-3Al2O3-67B2O3 (0 ⩽ x ⩽ 5; 0 ⩽ y ⩽ 5). In singly Nd3+ doped glasses, a slight site-to-site dependence of radiative decay rates has been observed using FLN spectroscopy. Nonexponential decays of neodymium emission were analyzed in terms of microparameters characterizing the probabilities of emission quenching by cross relaxation and of energy migration. In singly Yb3+ doped glasses, the 2F 5 2 → 2F 7 2 emission decay is always exponential. Energy migration over Yb3+ ions arises for y = 1.5 and an ultrafast migration is observed for y #62; 2. In Nd3+-Yb3+ co-doped glasses the Nd3+ → Yb3+ energy transfer probability is quite high. However, a Yb3+ → Nd3+ back transfer exists for low Yb3+ concentrations.

Nd3+, Eu3+, and Gd3+ ions as local probes in the NaxSr3−2xLnx(PO4)2 and KCaLn(PO4)2 rare earth phosphates

Abstract Use of Nd 3+ , Eu 3+ , and Gd 3+ as local structural probes allows the determination of the rare earth positions in the Na x Sr 3−2 x Ln x (PO 4 ) 2 ( Ln = La to Tb) and KCa Ln (PO 4 ) 2 phases ( Ln = rare earth). Moreover, a common feature of both series is a particularly high splitting of the excitation 6 P 7 2 and 6 P 5 2 levels of the Gd 3+ ions.

Luminescence of the Cu+ ion in CuLaO2

Abstract The investigation of the luminescent properties of the delafossite-type CuLaO2 oxide shows two emission bands; the emission band at lower energy results from the excitation to the highest energy level, thus exhibiting a higher Stokes shift. The existence of only one atomic site for Cu+ suggests a simple model involving two emitting levels: one is a localized state corresponding to an excited term of the 3d94s1 configuration and the other is an excitonic state.

The structure and luminescent properties of Mn0.5Zr2(PO4)3

The phosphate Mn0.5Zr2(PO4)3 can be obtained at high temperature (1400°C). It crystallizes in the rhombohedral system (space group R3) with parameters ah = 8.85(1) and ch = 21.80(5) A in the equivalent hexagonal cell. Its structure, determined by the Rietveld method, is typical of the Nasicon-type arrangement with a partial occupation of the two M(1) sites [(3a) and (3b)] generated by the space group. The magnetic and luminescent properties are consistent with the crystallographic data and give evidence of the existence of a small amount of Mn3+ in such as-prepared samples, the actual composition being Mn2+0.5–xMn3+2x/3Zr2(PO4)3 with x ≅ 0.03.

The solid solution BaLi1–xCuxPO4(x⩽ 0.5): an example of Cu+ single-ion luminescence in oxide insulators

The crystallographic and spectroscopic properties of the solid solution BaLi1–xCuxPO4(0 ⩽x⩽ 0.5) have been investigated as a function of temperature and monovalent copper concentration. A structural description of the compounds is proposed, on the basis of an isotypy with the hexagonal form of β-SiO2 trydimite. This description involves the existence of a 1:1 ordering between the cross-linked LiO4 and PO4 tetrahedra, in a way such that the replacement of lithium by copper cannot involve any direct Cu+–Cu+ interaction in the network. This argument is supported by the spectroscopic results. The materials exhibit a unique blue emission under UV excitation, whatever the temperature and the composition. This luminescence possesses a time-constant which is independent of the copper concentration. It is attributed unambiguously to Cu+ single ions.

Oxygen environment of rare-earth ions in phosphates with β-K2SO4 type structure

Abstract The use of europium as a local structure probe allowed the authors to determine the various phases appearing at room temperature in the NaPO 4 Na 3 Eu(PO 4 ) 2 and NaSrPO 4 Na 3 Eu(PO 4 ) 2 systems. The broadening of the europium emission lines in going from the calcium to the strontium phases illustrates the ease of movement of the [PO 4 ] groups.