Brunold Thomas C., Güdel Hans U.
Departement für Chemie, Freiestrasse 3, Universität Bern, CH-3000 Bern 9, Switzerland.
Inorg Chem. 1997 Apr 23;36(9):1946-1954. doi: 10.1021/ic9611711.
The first polarized low-temperature absorption and luminescence spectra of manganese-doped crystals of BaSO(4) containing essentially MnO(4)(2)(-) are reported. By using a flux composed of NaCl, KCl, and CsCl we were able to grow BaSO(4):Mn(6+) crystals below 620 degrees C. This prevents the simultaneous presence of MnO(4)(3)(-) besides MnO(4)(2)(-), which was mainly responsible for the erroneous assignments of the absorption spectrum in the literature. In the BaSO(4) host the MnO(4)(2)(-) ion occupies a site of C(s)() symmetry, and the orbital degeneracies of the E and T states are thus lifted. Above 16 000 cm(-)(1) the absorption spectra consist of a series of intense ligand-to-metal charge transfer (LMCT) excitations. Their marked polarization dependence allows an unambiguous band assignment in the parent T(d)() symmetry. The three origins of the (2)E --> (2)T(2) ligand-field (LF) transition peak at 11 074, 11 570, and 11 790 cm(-)(1). The lowest-energy component of (2)T(2) serves as the initial state for broadband luminescence in the near-infrared (near-IR) region with a maximum at 9300 cm(-)(1). Below 100 K the quantum yield is unity and the radiative lifetime is 2.75 &mgr;s, and at 300 K the quantum yield is still 20%. In both the (2)E <--> (2)T(2) (d --> d) absorption and luminescence spectra the vibrational structure is dominated by progressions in O-Mn-O bending modes whereas coupling to the totally symmetric Mn-O stretching mode is less pronounced. The luminescence band shapes for the transitions to the two orbital components of (2)E are strikingly different; the Huang-Rhys parameters for the bending-mode progressions obtained from fits of simulated band shapes to the experimental spectra are 1.3 and 3.7, respectively. This is due to weak E multiply sign in circlee and stronger T(2) multiply sign in circlee Jahn-Teller (JT) effects in the ground and excited LF states, respectively. The linear vibronic coupling constants are f(E)() approximately 180 cm(-)(1) and f(T)() approximately -730 cm(-)(1) and the corresponding JT stabilization energies E(JT)((2)E) approximately 50 cm(-)(1) and E(JT)((2)T(2)) approximately 780 cm(-)(1), respectively.
报道了含MnO₄²⁻的BaSO₄锰掺杂晶体的首个偏振低温吸收光谱和发光光谱。通过使用由NaCl、KCl和CsCl组成的助熔剂，我们能够在620℃以下生长BaSO₄:Mn⁶⁺晶体。这避免了除MnO₄²⁻之外同时存在MnO₄³⁻，而MnO₄³⁻是文献中吸收光谱错误归属的主要原因。在BaSO₄基质中，MnO₄²⁻离子占据Cₛ对称位点，因此E和T态的轨道简并性被消除。在16000cm⁻¹以上，吸收光谱由一系列强烈的配体到金属电荷转移（LMCT）激发组成。它们明显的偏振依赖性使得在母Tₑ对称中能够明确地进行能带归属。(²E)→(²T₂)配体场（LF）跃迁峰的三个起源分别位于11074、11570和11790cm⁻¹。(²T₂)的最低能量成分作为近红外（near-IR）区域宽带发光的初始态，其最大值在9300cm⁻¹处。在100K以下，量子产率为1，辐射寿命为2.75μs，在300K时量子产率仍为20%。在(²E)⇔(²T₂)（d→d）吸收光谱和发光光谱中，振动结构主要由O-Mn-O弯曲模式的进展主导，而与完全对称的Mn-O伸缩模式的耦合不太明显。向(²E)的两个轨道成分跃迁的发光带形状显著不同；从模拟带形状拟合实验光谱得到的弯曲模式进展的黄昆-里斯参数分别为1.3和3.7。这分别是由于基态和激发态LF态中E⊗和T₂⊗ Jahn-Teller（JT）效应较弱和较强所致。线性振子耦合常数分别为f(E)≈180cm⁻¹和f(T₂)≈ -730cm⁻¹，相应的JT稳定能E(JT)(²E)≈50cm⁻¹和E(JT)(²T₂)≈780cm⁻¹。
