Equation of state for Eu-doped SrSi2O2N2

Study of persistent luminescence and thermoluminescence in SrSi2N2O2:Eu2+,M3+ (M = Ce, Dy, and Nd)

The process of persistent luminescence or glow-in-the-dark, the delayed emission of light of irradiated substances, has long fascinated researchers, who have made efforts to explain the underlying physical phenomenon as well as put it to practical use. However, persistent luminescence is an elusive and difficult process, both in terms of controlling or altering its properties, as well as providing a quantitative description. In this paper, we used SrSi₂N₂O₂:Eu²⁺ as a model persistent phosphor, characterized by the broad distribution of structural defects and exhibiting long-lasting Eu²⁺ luminescence that is visible for a few minutes after switching off UV light. We investigated the persistent luminescence process by two complementary methods, namely, thermoluminescence and temperature-dependent persistent luminescence decay measurements. Analysis of experimental data allowed us to determine the depth distribution of traps, and allowed us to distinguish two different mechanisms by which the emission is delayed. The first, the temperature-dependent mechanism, is related to trap activation, while the second, temperature-independent mechanism is related to carrier migration. Finally, we employed the strategy of the co-doping of the phosphor SrSi₂N₂O₂:Eu²⁺,M³⁺ (M = Ce, Nd, Dy) to modify the persistent luminescence properties.

Structural phase transitions and photoluminescence properties of oxonitridosilicate phosphors under high hydrostatic pressure

Spectroscopic properties of a series of (Sr_0.98-xBa_xEu_0.02)Si₂O₂N₂ (0 ≤ x ≤ 0.98) compounds has been studied under high hydrostatic pressure applied in a diamond anvil cell up to 200 kbar. At ambient pressure the crystal structures of (Sr_0.98-xBa_xEu_0.02)Si₂O₂N₂ (0 ≤ x ≤ 0.98) are related to the ratio of strontium to barium and three different phases exists: orthorhombic Pbcn(0.78 ≤ x ≤ 0.98), triclinic P1 (0 < x ≤ 0.65) and triclinic P1 (0.65 < x < 0.78). It was found that Eu²⁺ luminescence reveals abrupt changes under pressure (decay time, energy and shape) which indicate the variation of the local symmetry and crystal field strength in Eu²⁺ sites. These changes are attributed to the reversible pressure-induced structural phase transitions of triclinic (Sr_0.98-xBa_xEu_0.02)Si₂O₂N₂ into orthorhombic structure. Pressure in which phase transition occurs decreases linearly with increasing of Ba composition in (Sr_0.98-xBa_xEu_0.02)Si₂O₂N₂ series. Additionally, very different pressure shifts of the Eu²⁺ luminescence in different phases of (Sr0.98-xBaxEu0.02)Si₂O₂N₂:Eu from −40 cm⁻¹/kbar to 0 cm⁻¹/kbar have been observed. This effect is explained by different interaction of the Eu²⁺ 5d electron with the second coordination sphere around the impurity cations.

A first-principles study of the electronic structure and mechanical and optical properties of CaAlSiN3

A systematic study of the basic characteristics of CaAlSiN₃.