Markku Leskelä

Luminescence properties of Eu2+, Sn2+, and Pb2+ in SrB6O10 and Sr1 − xMnxB6O10

Abstract The luminescence properties of Eu2+, Sn2+, and Pb2+ in SrB6O10 have been studied both at room-temperature and liquid-helium temperature and the decay times of Sn2+ and Pb2+ in this matrix have been measured and analyzed. According to the emission spectrum of Eu2+ there seems to be three different cation sites in SrB6O10. Europium, tin, and lead were also used as sensitizers for Mn2+ and the energy transfer processes were characterized. Eu2+-Mn2+ energy transfer was inefficient due to the transfer within different Eu2+ centers. The sensitization action of Sn2+ and Pb2+ on Mn2+ was different because lead-lead energy transfer occurs (even at 4.2 K) but tin-tin transfer can be neglected. A fast diffusion model for the Pb2+ system is suggested.

Fluorescence spectrum, energy level scheme and crystal field analysis of europium(+III) doped lanthanum magnesium borate LaMgB5O10:Eu3+

The fluoresence spectrum of europium(+III) doped LaMgB5O10 was studied at 77 and 300K under U.V. and visible dye laser excitation. A phenomenological crystal field analysis was conducted on the basis of the observed 34 7 F 0-5 level energies. A descending symmetry method from D 2d to C 2v and C 2 symmetries was used in the simulation. D 2d simulation was found to be inadequate to describe the experimental energy level scheme whereas for C 2v symmetry a satisfactory r.m.s. deviation of 7·1 cm-1 was obtained. The decrease in symmetry to C 2 did not improve the simulation. The weak 5 D 0 → 7 F 0 transition intensity was found to correlate with the mixing of the 7 F 2,4 wave functions with the 7 F 00 one.

Site selectively excited luminescence of Eu3+ in gadolinium, yttrium and lutetium oxyorthosilicates☆

Abstract In the present study the optical properties of the Eu3+-activated rare earth oxyorthosilicate, RE2(SiO4)O:Eu3+ (RE ≡ Gd, Y, Lu) powder samples were investigated. The luminescence spectra were recorded at 77 K using site selective excitation by a dye laser in addition to conventional UV excitation. Strong luminescence was observed only from the 5D0 level. Site selective excitation gave two sites for the Eu3+ ion in all oxyorthosilicates studied. In lutetium and yttrium compounds the sites are deduced to be very similar since only small differences exist in the 5D0 → 7F0 transition energies, and because the 7Fj level schemes resemble each other. The absence of degeneracy in the 7Fj levels indicates low symmetry for both sites, which are rather different. In gadolinium oxyorthosilicate the two cation sites differ significantly from each other. The emission from one of the sites showed doubled peaks probably due to local distortions.

Luminescent properties of Ce3+ and Tb3+ in SrB6O10 and BaB8O13

Abstract The luminescence of Ce3+ and Tb3+ in SrB6O10 and BaB8O13 has been studied, also using Ce3+ and Tb3+ codoped samples. The excitation spectrum of Ce3+ in both matrices contains several bands between 260 and 320 nm. The emission spectrum of Ce3+ also has several maxima between 300 and 360 nm. In addition, there is a broad band at 515 nm in BaB8O13. The results indicate that in both matrices the Ce3+ ion may occupy several sites. The 4f-5d excitation band of Tb3+ lies below 210 nm in both compounds. The emission of Tb3+ shows typical peaks from the 5D4 level, having the most intense line at 542 nm. Sensitization of Tb3+ emission with Ce3+ is possible in these matrices and a bright green emission is observed. Addition of alkali ions for charge compensation significantly affects the emission intensities.

Preparation of yellow and red iron oxide pigments from iron(II) sulfate by alkali precipitation

Abstract A study was made of the preparation of yellow α-FeOOH pigments from iron(II) sulfate solution by alkali precipitation and gas oxidation methods. The preparation of pure yellow pigments turned out to be difficult. Pigments of composition FeOOH were obtained under acidic (pH 3 O 4 was formed as well, and it stained the products greenish, brownish or black. At 70°C and pH 7–9 a pure black Fe 3 O 4 was formed. According to TG measurements, the needle-like FeOOH particles decomposed to red α-Fe 2 O 3 above 300°C and the pigments then obtained were light red. The preparation of dark red oxides required higher temperatures than the direct firing of FeSO 4 ·7 H 2 O to oxide.

Thermal stability of Eu3+ activated rare earth hydrogenselenites

Abstract The thermal behaviour of Eu3+ activated rare earth (La, Gd, Y, Lu) hydrogen selenite hydrate was studied. After dehydration REH(SeO3) decomposes to corresponding selenite at 670-77 K depending on the rare earth. The selenite decomposes further to oxyselenite at about 970 K. The stability range of the oxyselenite phase is 100–150 degrees decrasing with decreasing with decreasing ionic radius. The behaviour of lanthanum compound differs from that of the others, The Eu3+ luminescence was found to be a sensitive probe of the thermal decomposition scheme of rare earth hydrogense lenites.

Site-selective excited luminescence of Eu3+-doped lutetium oxyselenite

Abstract The luminescence properties of an Eu3+-doped lutetium oxyselenite, (LuO)2SeO3:Eu3+, were investigated at 77 K under both UV and dye-laser excitation. The complex UV-excited luminescence spectrum resolves into two well-resolved spectra with the use of site-selective excitation. The two spectra resemble each other and therefore the corresponding sites cannot be very different, either. The two Ln sites are of low symmetry since the degeneracy of the 7FJ levels was totally lifted. The spectra of both the sites are very similar to the spectra of several other Ln oxysalts containing the tetragonal type of (LnO)n+n complex cation as a common structural unit.

Determination of cerium, europium and terbium in rare earth matrices by DCP-AES☆

Abstract Direct current plasma atomic emission spectrometry (DCP-AES) was used for the determination of cerium, europium and terbium in rare earth matrices. The interference effect of the matrix elements of rare earth phosphors (yttrium, lanthanum, gadolinium and lutetium) and vanadium, phosphorus, sulphur, boron, silicon, aluminium, magnesium and barium was investigated. Considerable spectral interferences from the rare earth elements were found at most of the emission lines studied. The other elements studied caused only minor interference. By using suitable emission lines (418.66 nm for cerium, 282.08 nm for europium and 332.44 nm for terbium), cerium, europium and terbium can be determined in yttrium, lanthanum, gadolinium and lutetium matrices, but in some cases the use of a background compensator is necessary.

A Thermal study of the precipitates formed in ammonia neutralization of acidic solutions of dissolved phlogopite

The precipitates containing mainly iron, aluminium and magnesium hydroxides, obtained from phlogopite dissolved in nitric acid by means of the neutralization procedure with ammonia, have been investigated by thermal analysis (TG, DTG and DTA). According to the present study, which is part of a larger investigation into the chemical utilization of Finnish mica minerals, the formation of solid solutions between iron and aluminium hydroxides in silt increases with an increasing neutralization temperature. Nitrogen exists mainly in the form of nitrate in silts, and magnesium forms mixed hydroxides with aluminium, which causes a separation between the iron hydroxide and magnesium aluminium hydroxide phases.ZusammenfassungDie von in Salpetersäure gelöstem Phlogopit durch Neutralisierung mit Ammoniak erhaltenen, hauptsächlich Eisen-, Aluminium- und Magnesiumhydroxid enthaltenden Niederschläge wurden thermoanalytisch (TG, DTG und DTA) untersucht. In der vorliegenden Arbeit, die Teil einer grossangelegten Untersuchung zur chemischen Nutzung finnischer Glimmermineralien ist, wird gezeigt, dass die Bildung fester Lösungen von Eisen- und Aluminiumhydroxiden in Schluff mit zunehmender Neutralisationstemperatur ansteigt. Stickstoff kommt in Schluff hauptsächlich in Form von Nitraten vor, und Magnesium bildet Mischhydroxide mit Aluminium, was eine Trennung der Eisenhydroxidphase von der Magnesium-Aluminium-Hydroxidphase bewirkt.РезюмеМетодами ТГ, ДТГ и ДТА и сследованы осадки, содержащие главным образом гидр оокиси железа, алюмин ия и магния. Осадки были получены раство рением флогопита в аз отной кислоте с последующе й нейтрализацией амми аком. Согласно провед енных исследований, являющихся частью ко мплексного исследов ания по химическому использованию финск их минералов, образов ание твердых растворов между гидр оокисями железа и алю миния в осадке увеличиваетс я с увеличением темпер атуры нейтрализации. Азот находится в осадке, главным обра зом, в форме нитрата, а магний образует смешанные гидроокис и с алюминием, что вызы вает разделение между гидроокисью же леза и смешанной гидр оокисью магний алюминия.