Defects and luminescence behavior of cubic F23 [(NH4(18-Crown-6))4MnX4] [TlX4], (X = Cl, Br) crystals

Luminescence from [(NH4(18-Crown-6))(4)MnBr4][TIBr4](2) (1), [(NH4(18-Crown-6))(4)NH4Cl4][TICl4](2) (2), [(NH4(18-Crown-6))(2)MnBr4] (3), and [(NH4(18-Crown-6))(2)MnCl4] (4) was studied in search of new insights regarding crystal defects in 2. Emission from 3 and 4 is normal Mn2+(T-4(1)((4)G) --> 6A(1)); that of 2 (lambda(max) 520 nm at ca. 300 K and 560 nm at 77 K) is unusual and temperature dependent. Thermal barriers (kj/mol, assignment): green emission of 1 and 2, T < 150 K (1-2, NH4+ rotations), 150 < T < 250 K (7-14, energy migration among [MnX4](2-)), 250 < T < 300 K (26-35, rotations of 18-Crown-6)); yellow emission of 2: T < 250 K (7-8, energy migration among [MnX4](2-)), T > 250K (29 kJ/mol, defect-to-Mn2+(4T(1)((4)G)) back energy transfer). Crystal data for 4: Space group P2(1)/c; Z = 4; a = 20.173(1) Angstrom; b = 9.0144(8) Angstrom; c = 20.821(1) Angstrom; beta = 98.782(5)degrees; V= 3741.9(8) Angstrom(3); R-w = 0.059; R = 0.054. (C) 2002 Elsevier Science.