The persistent phosphorescence and thermoluminescence of SrAl₂O₄:Eu²⁺:Dy³⁺ is reported for a variety of different excitation wavelengths and excitation temperatures, to provide new insights in the mechanism of the trapping and detrapping. These measurements reveal that the trapping is strongly dependent on the wavelength and temperature. First, with increasing loading temperature, the thermoluminescence peak shifts to lower temperatures which corresponds to a change of trap population. Secondly, the integrated thermoluminescent intensity increases with increasing loading temperature. All wavelength and temperature dependent experiments indicate that the loading of the traps is a thermally activated processes. Utilizing different wavelengths for loading, this effect can be enhanced or reduced. Furthermore excitation with UV-B-light reveals a tendency for detrapping the phosphor, reducing the resulting thermoluminescent intensity and changing the population of the traps.

Single crystals of tetragonal RCuGa₃ (R=La, Pr, Nd and Gd), with BaNiSn₃ type structure (space group I4 mm), have been grown by high temperature solution growth technique using Ga as flux. Their magnetic properties were determined by heat capacity and the measurement of magnetization and electrical resistivity along [100] and [001] directions. Except LaCuGa₃, the compounds order magnetically. PrCuGa₃ undergoes a ferromagnetic transition with Curie temperature of 4.6 K. NdCuGa₃ shows a bulk magnetic transition at 3.3 K. The data on GdCuGa₃ indicate combined characteristics of spin glass and antiferromagnetic behavior at low temperatures. From the Schottky heat capacity data the crystal electric field level energy spectra have been determined. Further we have performed temperature dependent measurements of electron spin resonance (ESR) on GdCuGa₃ between 11 K and room temperature. The ESR data indicate an enhancement of magnetic fluctuations associated with spin reorientation and both homogeneous and inhomogeneous thermal broadening of the linewidth.

Europium doped crystalline Ba₇F₁₂Cl₂ phosphors have been prepared at temperatures between 650 and 900 °C using alkali chloride fluxes, yielding both disordered (with the incorporation of small amounts of Na) and ordered crystal modifications. The white emission spectrum excited in the near UV consists roughly of two broad emission bands at ca 450 and 590 nm, as well as weak sharp Eu²⁺ 4f-4f emission bands around 360 nm. The incorporation of Eu²⁺ is further studied using EPR spectroscopy on single crystals, and reveals a significant zero field splitting. The emission spectrum can be significantly tuned by varying the excitation wavelength between 300 and 390 nm. Fine tuning may also be achieved by chemical substitutions to form Ba_7-xM_yF₁₂Cl_2-zBr_z (M = Na, Ca,Eu). Quantitative measurements of the light produced using commercial near UV LEDs show that the color temperature ranges between 4000 and 9700 K with CIE chromaticity coordinates close to the ideal values of x=y=0.333. The best color rendering index (CRI) found was 0.83, and the highest light to light conversion yield was 171 lumen/W. These results show that the title compound is a very promising candidate for white light generation using near UV LED excitation.

We have studied the solid-liquid equilibrium of the system Sr_1–yBa_yFCl_1–xBr_x using DTA and X-ray diffraction techniques. The entire composition range in this system yields solid solutions which crystallize in the PbFCl (Matlockite) structure type. The melting points of the entire composition range have been parametrized (within 5°C rms error) using a biquadratic fit of the available data obtained by experiment and from the literature.

A recent investigation of the (BaF₂–MgF₂) phase diagram produced several new compounds which are suitable hosts for Rare Earth impurities. We present results on single crystals of Ba₂Mg₃F₁₀ doped with Eu²⁺. The local structure and optical properties of this system were investigated by luminescence emission and by EPR. We observed two different Eu²⁺ sites. Both show C_s point symmetry and an important ground state splitting. Correlating our EPR and optical results with the new Ba₂Mg₃F₁₀ structure data allowed the assignment of each of them to a specific barium lattice site. The luminescence emission of both the 4f⁷–4f⁶5d and the 4f⁷–4f⁷ transitions is observed. The relative importance of the two emissions is strongly temperature dependent. The emission intensities of the intra f-shell ⁶P_7/2→⁸S_7/2transitions increase strongly on going from 295 K to 77 K. Thus, the lowest levels of the 4f⁶5d configuration are approximately degenerate with the ⁶P_7/2 manifold.

Eu²⁺ was introduced into pure and oxygen codoped BaMgF₄ single crystals. A detailed EPR study of this ion (S=7/2) was realized on both types of systems. The result is that only one spectrum was observed involving a strong crystal field. The associated site symmetry of the impurity is C_s. It occupies very closely a Barium lattice site as was established by correlating the EPR results with those of a refined X-ray structure analysis on a Ba_0.8Eu_0.2MgF₄ single crystal realized in our laboratory. The oxygen codoped crystals exhibited this same Eu²⁺EPR spectrum (the only one). Optical emission and excitation experiments were performed between 13 000 and 53 000 cm^−1. The results due to the Eu²⁺ impurity are given and discussed qualitatively within the 4f⁷ ↔ 4f⁶5d¹Â scheme.

When modern spectral hole burning applications for high-density information storage under noncryogenic temperatures are envisioned, it is necessary to develop new frequency-selective photoactive materials for this purpose. Mixed compounds of the PbFCl family, doped with samarium(II) ions, exhibit promising and true room-temperature hole burning capabilities. We investigate this class of systems (and related ones) by combining material synthesis and high-resolution spectroscopy. Whole groups of isomorphous crystals were synthesized with varying degrees of halide anion and/or cation substitutions. Thin films of fluoride-based materials were made in a laboratory-built molecular beam epitaxy system. An extended x-ray study, differential thermal analysis, luminescence, and Raman measurements allowed the characterization of the materials. Formal models were developed for both the inhomogeneous zero-phonon optical line shapes of the samarium(II) and the time evolution of the hole burning.

The 3,6-substituted 1,2,4-trioxan-5-ones 11-14, on heating to 170-200°, underwent unimolecular thermolysis to generate electronically excited singlet ketones with an efficiency of ca. 0.2%. The chemiluminescence quantum yields (ΦoS_CL) depended on the nature of the 6-substitutents and increased linearly with temperature. The Arrhenius activation energies were obtained by measuring the rate of decay of luminescence and determined as 22.9, 30.4, 35.6, and 34.2 kcal/mol for 11-14, respectively. Step analysis of the chemiluminescence of 14 afforded an average activation energy of 44.3 kcal/mol. This latter result is explicable in terms of two decomposition paths, higher and lower in energy, leading to excited and 'dark' products, respectively. The thermolysis of trioxanones 12-14 lacking a H-atom at the 6-position is interpreted as involving successive rupture of the peroxide bond, excision of ketone at the 3-substituted end, and loss of CO₂, to finally produce ketone originating from the 6-position (see Scheme 4).

The ESR of small concentration of Gd 0.03<y<0.06 substituting for Y in single crystals of Gd_yY_1−yBa₂Cu₃O_6−x has been measured. In the insulating compound, with x ~ 0.1, and the superdconducting materials with 30 K < T_c < 80 K, the measurements were performed at X-band, 9.3 GHz, and K_α-band, 36 GHz, over a large temperature range above T_c. Angular dependence measurements exhibit a spectrum which is fully resolved in certain directions, but only partially resolved, because of exchange narrowing, in other directions. Comparisons between the spectra in the insulating and superconducting compounds shows similar angular dependent behavior. This seems to indicate that the origin of the exchange narrowing is the same in both compounds. Since this narrowing in the insulating compound arises from interaction with, or via, the Cu magnetic system, it is implied that there is a similar, perhaps fluctuating, system in the superconducting state. Preliminary measurements of the temperature dependence of the line widths may indicate the presence of spin pairing at about 110 K, above the actual T_c of 70 K. The crystal field parameters are D = 3B⁰₂ = 1307 MHz, B⁰₄ = 3.014 MHz and B⁴₄ = -11.43 MHz, for the semiconducting sample. The g-value is 1.989 ± 0.005. These values change only slightly in the superconducting crystals.

ESR results are reported on the Ag²⁺ ion introduced into alkaline earth fluoride crystals. In SrF₂ (as in CaF₂) a trigonal centre is present which tunnels between four equivalent C₃ directions as shown by ESR under uniaxial stress. A T_2g ⊗ t_2g Jahn-Teller model describes adequately the paramagnetic and stress effects when the strong coupling case is considered. Ag²⁺ in BaF₂ forms a static tetragonal cluster similar to Ag²⁺ and Cu²⁺ in SrCl₂.