S. Gutzov

Cathodoluminescence study of europium-doped zirconia and cassiterite powders

Abstract The cathodoluminescence spectra of ZrO 2 :Eu 3+ powders of average crystallite size 15–35 nm and SnO 2 :Eu 3+ powders of crystallite size 40–50 nm, obtained after different heat treatments, were studied. The change in the room-temperature cathodoluminescence spectra of Eu 3+ , measured between 400 and 750 nm by 4–15 kV excitation, showed that prolonged heat treatment (24 h/950 °C) leads to the formation of non-centrosymmetric Eu 3+ sites in both systems. In the ZrO 2 :Eu 3+ systems two spectrum types were detected, for samples heated at relatively low and high temperatures, respectively. These observations are explained qualitatively by the formation of different configurations of oxygen vacancies in the process of crystal growth under heat treatment. Quantitative cathodoluminescence measurements show an increase of the luminous efficiency of the powders which is connected with particle agglomeration during heat treatment.

Luminescence of sol–gel-derived silica doped with terbium-benzoate complex☆

Abstract Various approaches to prepare sol–gel-derived silica doped with luminescent lanthanoid complexes have been already demonstrated in several studies. The applicability of these materials as phosphors for practical purposes depends on the quantum efficiencies achievable as well as on the excitation characteristics. This work describes the excitation spectrum of such hybrid materials down to the VUV region and gives quantitative figures for the quantum efficiencies under 254 nm excitation.

Optical properties of europium containing zirconium oxynitrides

Abstract Eu–Zr–O–N ceramics containing up to 10 mol% Eu 2 O 3 and 7 mol% nitrogen were synthesised by nitridation of europium doped zirconia materials in a nitrogen atmosphere at temperatures between 1600 and 1900 °C. Chemical and structural analyses of the samples depict a correlation between the stability of the observed fluorite-related phases and the concentration of the anion vacancies due to the incorporation of nitrogen and europia. The optical properties of quaternary Eu(III)–Zr–O–N phases are discussed in detail. Little amounts of nitrogen incorporated in the crystal lattice of Zr–Eu–O ceramics dramatically change the optical properties.

Highly efficient energy transfer from Ge-related defects to Tb3+ ions in sol–gel-derived glasses ☆

Abstract Luminescence and excitation spectra of sol–gel derived silica co-doped with Ge and Tb and treated in reducing atmosphere are reported. Energy transfer from Ge-related defects to Tb centers is demonstrated with an efficiency close to unity, resulting in all-inorganic sol–gel-derived materials with up to 30% quantum efficiency upon excitation under 254 nm radiation.

Effect of germanium-codoping on the luminescence of terbium doped silica xerogels

Abstract The luminescence and excitation spectra of sol–gel derived silica containing up to 7.5 mol% Tb as well as of silica containing 1 mol% Tb and additionally up to 12 mol% Ge are reported. At 355 nm excitation, we demonstrate an increase of the Tb emission intensity due to Ge incorporation. The excitation spectra of both Tb and Tb–Ge doped silica change after heat treatment. We conclude, that electronic as well as structural defects play an important role for the Tb luminescence in silica xerogels.

Preparation and optical properties of Zr–Ce–O–N materials

Abstract Zr–Ce–O–N ceramics containing up to 10 cation% Ce and 15 anion% N have been prepared by the nitridation of Zr–Ce–O pellets at 1600–1900°C and PN2 pressures between 1.4 and 1.6 bar. The phase relationships of the prepared materials are investigated using XRD. UV/V is reflectance spectra analysis shows that nitrogen incorporation changes the optical properties of Zr–Ce–O ceramics causing a brown–red coloration whose intensity depends on the nitrogen amount.

High temperature optical spectroscopy of cubic holmium doped zirconia, Zr0.78Y0.21Ho0.01O1.90

The electronic absorption spectra of a Zr0.78Y0.21Ho0.01O1.90 single crystal have been measured in in situ conditions between room temperature and 1289 K. The evolution of the spectra with rising temperatures is characterised by an overall increase in intensity. Notably the intensities of the 5I8 → 5F2, 5I8 → 5S2 and 5I8 → 5G6 transitions increase by factors of two to three. The evaluation of the spectral parameters favours the conclusion that the intensity increases are due to vibronic coupling associated with effective frequencies ranging between 1 × 1013 and 5 × 1013 s−1 (330 cm−1 and 1670 cm−1). The changes in the optical spectra are reversible and are not connected with structural changes in the material.

High temperature optical spectroscopy investigations on Zr0.78Y0.18Sm0.04O1.89 and Zr0.78Y0.18Ho0.04O1.89 single crystals

Results are reported from a temperature dependent optical study of the title compounds performed at temperatures up to 1323 K. Absorption maxima and integrated absorption of rare earth f-f transitions exhibit a considerable temperature dependence, which is quantitatively described in the framework of the optical high temperature spectroscopy of d-ions. A strong, reversible band gap shift of doped and pure YSZ is observed and evaluated according to the Tauc equation. Single crystals of the title compounds were prepared by the skull melting method. Their linear expansion coefficients were determined by high-temperature X-ray diffraction.

Functionalization of Sol-Gel Zirconia Composites with Europium Complexes

Different sol-gel strategies based on functionalization of ZrO2:Eu microparticles with 1,10- phenanthroline (phen) and incorporation of colloidal Eu(phen)2(NO3)3 into zirconia have been used to obtain hybrid sol-gel composites with controlled optical properties. The process leads to materials with quantum yields of about 48% monitoring the 615 nm emission line at 350 nm excitation. Excitation/ luminescence spectroscopy, diffuse reflectance spectroscopy and X-ray diffraction have been used to characterize the hybrid zirconia composites. Graphical Abstract Functionalization of Sol-Gel Zirconia Composites with Europium Complexes

Preparation and spectral properties of europium hydrogen squarate microcrystals

A simple scheme for preparation of europium hydrogen squarate octahydrate microcrystals, Eu(HSq)3·8H2O is demonstrated. The microcrystalline powders obtained have a potential application as non-centrosymmetric and UV radiation - protective hybrid optical material. The site-symmetry of the Eu - ion is C2V or lower, obtained from diffuse reflectance spectra. The formation of europium hydrogen squarate is supported by IR - spectroscopy, UV-vis spectroscopy, chemical analysis and X-ray diffraction. A detailed analysis of the UV-vis and IR spectra of the micropowders prepared is presented.