Defects and luminescence behavior of cubic F23 [(NH₄(18-Crown-6))₄MnX₄] [TIX₄]₂ (X = CI, Br) crystals

Abstract

Luminescence from [(NH4(18-Crown-6))4MnBr4][TlBr4]2 (1), [(NH4(18-Crown-6))4MnCl4][TlCl4]2 (2), [(NH4(18-Crown-6))2MnBr4] (3), and [(NH4(18-Crown-6))2MnCl4] (4) was studied in search of new insights regarding crystal defects in 2. Emission from 3 and 4 is normal Mn2+(4T1(4G) →6A1); that of 2 (λmax ≈ 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>250 K (29 kJ/mol, defect-to-Mn2+(4T1(4G)) back energy transfer). Crystal data for 4: Space group P21/c; Z = 4; a = 20.173(1) Å; b = 9.0144(8) Å; c = 20.821(1) Å; β = 98.782(5)°; V = 3741.9(8) Å3; Rw = 0.059; R = 0.054. © 2002 Elsevier Science.