Photoluminescence properties of tunable emission (Sr1-Eu )2Ga2S5 phosphors

Photoluminescence properties of Eu2+‐activated thiogallate phosphors

“…37 The second category includes the BaGa 2 S 4 :Eu 2+ phosphor, which has cubic geometry with Pa3 symmetry and in which the Eu 2+ cations occupy two different sites surrounded by six S 2À anions in octahedral (O h ) symmetry and 12 S 2À anions in icosahedral (I h ) symmetry. Therefore, 29,38 the 5d orbitals of the excited states in the Eu 2+ ions are split into three levels: t 2g (5d z 2 , 5d x 2 Ày…”

“…In the case of the Sr 2 Ga 2 S 5 :Eu 2+ phosphor, the Eu 2+ cations are surrounded by seven S 2À anions in monocapped trigonal prism symmetry. 26,38 The 5d orbitals of the excited states in the Eu 2+ ions are split into five different levels: a 1 (5d x 2 Ày 2 ), b 2 (5d yz ), b 1 (5d zx ), a 1 (5d z 2 ), and a 2 (5d xy ). 39 Figure 1 shows the crystal structure at the center of the Eu 2+ ion and the energy-level splitting of the 5d orbitals of three categories of these six Eu 2+ -activated thiogallates.…”

“…Because the covalence effect of Eu 2+ -activated thiogallates is much larger than that of Eu 2+ -activated oxides, Eu 2+ -activated thiogallates are adequate for the application of the pc-WLEDs pumped by the blue LEDs. 14 Figure 3 ΔS (eV) 0.24 [29] 0.26 [28] 0.26 [29] 0.26 [28] 0.16 [29] 0.28 [22] 0.38 a 0.5 [28] 0.22 [38] 0.14 [38] D (eV) 1.73 [29] 1.71 [28] 1.62 [29] 1.62 [28] 1.75 [29] 1.63 [22] 1.35 a 1.3 [28] 1.72 [38] 1.91 [38] T 0.5 ( C) 125 [28] 200 [28] 180 [26] 145 [28] 6 0 [ 26] CIE coordinate (x, y) (0.42, 0.55) [29] (0.28, 0.66) [29] (0.33, 0.58) [29] (0.22, 0.57) a (0.38, 0.60) [38] (0.51, 0.49) [38] Note: [26,29,38]: Our reported papers. a This work.…”

“…The members of the third category—Sr 2 Ga 2 S 5 :Eu 2+ and Eu 2 Ga 2 S 5 —have orthorhombic geometry with Pbca symmetry. In the case of the Sr 2 Ga 2 S 5 :Eu 2+ phosphor, the Eu 2+ cations are surrounded by seven S 2− anions in monocapped trigonal prism symmetry 26,38 . The 5 d orbitals of the excited states in the Eu 2+ ions are split into five different levels: a 1 (5 d x 2 − y 2 ), b 2 (5 d yz ), b 1 (5 d zx ), a 1 (5 d z 2 ), and a 2 (5 d xy ) 39 …”

“…Excess S was used to prevent the formation of gallates instead of thiogallates. The mixtures were placed in alumina crucibles and heated to appropriate temperatures in the range from 800 to 1100 C. A double-crucible system was used, in which activated carbon was filled between the inner crucible containing the reagents and the outer crucible to prevent oxidation of the Eu 2+ ions of EuS to Eu 3+ ions 29,38,42. The concentration of the Eu 2+ -activator was fixed at 5 mol% for CaGa 2 S 4 :Eu 2+ , SrGa 2 S 4 :Eu 2+ , and Sr 2 Ga 2 S 5 :Eu 2+ and at 10 mol% for BaGa 2 S 4 :Eu 2+ .…”