Karol Szczodrowski

Stabilization of Eu3+ under a reductive atmosphere by the Al3+ co-doping of Sr2SiO4:Eu2+/Eu3+

Two series of materials based on a strontium orthosilicate matrix doped with europium and different concentrations of aluminum ions were obtained using different solid state synthesis strategies. The phase composition of the samples was investigated using the X-ray diffraction (XRD) technique. The results of the optical characterization indicated that the incorporation of aluminum ions causes the stabilization of the Eu3+ ions under reductive atmosphere. The concentration ratio of europium ions incorporated into the matrix in both oxidation states ([Eu3+]/[Eu2+]) can be controlled by changing the Al3+ concentration. The observed effect is interesting from the point of view of the design of phosphors used to obtain white light emitting diodes (WLEDs). The influence of temperature on the relative intensity of Eu2+ and Eu3+ emission bands was studied to investigate the range of the impact of the created compensation defects. It is shown that the Eu3+ to Eu2+ reduction process in Sr2SiO4 takes place due to the migration of the strontium vacancies to the surface.

Equation of state for Eu-doped SrSi2O2N2

α-SrSi2O2N2 is one of the recently studied oxonitridosilicates applicable in optoelectronics, in particular in white LEDs. Its elastic properties remain unknown. A survey of literature shows that, up to now, nine oxonitridosilicate materials have been identified. For most of these compounds, doped with rare earths and manganese, a luminescence has been reported at a wavelength characteristic for the given material; all together cover a broad spectral range. The present study focuses on the elastic properties of one of these oxonitridosilicates, the Eu-doped triclinic α-SrSi2O2N2. High-pressure powder diffraction experiments are used in order to experimentally determine, for the first time, the equation of state of this compound. The in situ experiment was performed for pressures ranging up to 9.65 GPa, for Eu-doped α-SrSi2O2N2 sample mounted in a diamond anvil cell ascertaining the hydrostatic compression conditions. The obtained experimental variation of volume of the triclinic unit cell of α-SrSi2O2N2:Eu with rising pressure served for determination of the Birch-Murnaghan equation of state. The determined above quoted bulk modulus is 103(5) GPa, its first derivative is 4.5(1.1). The above quoted bulk modulus value is found to be comparable to that of earlier reported oxynitrides of different composition.

The influence of charge compensation defects on the spectroscopic properties of europium doped Ca9Y(PO4)7

In this study, a series of Ca9Y(PO4)7 compounds doped with 5% of Eu ions and with different [Y]/[Ca] ratios was synthesized using the Pechini method. Due to the presence of two different cations in the studied matrix (Ca2+ and Y3+) that are available for europium substitution, the synthesis parameters were selected to obtain the incorporation of the europium ions (5% mol) into the calcium sites only. The phase composition as well as elemental analysis and the spectroscopic measurements, carried out before and/or after the reduction of Eu3+ were performed to characterize the obtained phosphors. The XRD patterns show that in all cases the obtained materials consist of pure phase of Ca9Y(PO4)7. PLE and PL spectra measured before the reduction indicate that for the materials with the excess of yttrium, an additional Eu3+ site is observed which was not observed for materials with a deficiency of yttrium. For samples obtained after the reduction, the luminescence of Eu2+ depends on the changes of the Y/Ca ratio. The observed differences in Eu2+ luminescence are discussed taking into account the creation of different compensation defects depending on change of the Y/Ca ratio.