The photoluminescence (PL) in the visible spectral range of Ca 0.5 Ba 0.5 Ga 2 S 4 solid solutions activated with ions of rare-earth elements Eu 2+ and Er 3+ has been studied in the temperature range of 10-300 K. The PL spectrum contains a strong luminescence band peaking at 530 nm, which is due to the 4 f 6 5d → 4 f 7 transitions in Еu 2+ ions and weak lines in the range of 650-675 nm, which are due to the 4 F 9/2 → 4 I 15/2 transitions in Er 3+ ions. The position of the PL spectrum and the total PL intensity are characterized by high temperature stability in the range of 10-300 K; the total PL intensity decreases by only 13% with respect to the maximum value at 10 K. The PL decay time and the activation energy of nonradiative recombination channels are found to be τ e = 291 ns and E a = 41 meV, respectively.
INTRODUCTIONPhotoluminescence (PL) of ions of rare-earth elements (REEs) in wide-gap semiconductors has been intensely investigated, because these compounds are characterized by high luminescence efficiency due to the excitation of REE-ion PL through the semiconductor matrix [1][2][3]. A study of the luminescence properties of REEs in semiconductors and insulators yields information about the nearest REE environment and the symmetry of PL centers and crystal field. Ternary alkali-earth chalcogenide semiconductors of the II-III 2 -VI 4 type (II: Ba, Sr, or Ca; III: Ga or Al; and VI: S, Se, or O), activated by REE (Eu, Ce, Er, Yb, Pr, or Sm) ions, are promising phosphors.Calcium thiogallates doped with Еr 3+ ions exhibit strong Stokes and anti-Stokes luminescence in the visible spectral range at wavelengths of 530 nm ( 2 H 11/2 → 4 I 15/2 ), 550 nm ( 4 S 3/2 → 4 I 15/2 ), and 660 nm ( 4 F 9/2 → 4 I 15/2 ) and in the near-IR region at 870-920 nm ( 4 S 3/2 → 4 I 13/2 ), 976 nm ( 4 I 11/2 → 4 I 15/2 ), and 1530 nm ( 4 I 13/2 → 4 I 15/2 ) [4,5]. Barium, strontium, and calcium thiogallates activated by Eu 2+ ions are efficient phosphors emitting in the blue-green spectral region due to the 4 f 6 5d → 4 f 7 electronic transitions [6][7][8][9][10].Luminescence efficiency can be increased using more than one type of REE ions as dopants due to the excitation-energy transfer from one REE ion to another. In particular, in barium thiogallates activated