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Spectroscopic properties of a series of (Sr 0.98-x Ba x Eu 0.02 )Si 2 O 2 N 2  (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-x Ba x Eu 0.02 )Si 2 O 2 N 2  (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 Eu 2+  luminescence reveals abrupt changes under pressure (decay time, energy and shape) which indicate the variation of the local symmetry and crystal field strength in Eu 2+  sites. These changes are attributed to the reversible pressure-induced structural phase transitions of triclinic (Sr 0.98-x Ba x Eu 0.02 )Si 2 O 2 N 2  into orthorhombic structure. Pressure in which phase transition occurs decreases linearly with increasing of Ba composition in (Sr 0.98-x Ba x Eu 0.02 )Si 2 O 2 N 2  series. Additionally, very different pressure shifts of the Eu 2+  luminescence in different phases of (Sr0.98-xBaxEu0.02)Si 2 O 2 N 2 :Eu from −40 cm −1 /kbar to 0 cm −1 /kbar have been observed. This effect is explained by different interaction of the Eu 2+  5d electron with the second coordination sphere around the impurity cations.

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