Markus Herren

High-resolution near-infrared luminescence of mangenese(V) in tetrahedral oxo coordination

Abstract Manganese(V)-doped crystals of Ba5(PO4)3Cl (apatite structure) and Ca2VO4Cl (spodiosite structure) exhibit highly resolved photoluminescence in the near-infrared. It is assigned to intraconfigurational 1Ea3A2 (Td notation) transitions, and the vibrational sideband structure is interpreted in terms of bending and stretching vibrations of the (MnO4)3− entity. In lightly doped samples of the apatite compound, both the intensity and the lifetime of the luminescence (τ10 K=0.41 ms) drops by an order of magnitude between 10 K and room temperature.

Luminescence properties of Mn5+ in a variety of host lattices: Effects of chemical and structural variation

The optical spectroscopic properties of Mn5+ doped into ten host lattices have been studied. The influence of both chemical variation [phosphates(V), arsenates(V), and vanadates(V)] and structural variation (spodiosites, apatites, and Li3PO4‐type salts) on the luminescence properties is studied in detail. By varying the host lattice, the position of the sharp luminescence band can be varied from 8300 to 8960 cm−1. Excited state splittings, luminescence lifetimes, and sideband intensities are correlated with the geometrical distortion of the MnO3−4 tetrahedron. In all the host lattices, the luminescence originates from the 1E excited state at all temperatures. It is essentially unquenched at room temperature in apatite and Li3PO4‐type lattices, whereas in spodiosites up to 90% of the luminescence may be quenched at room temperature.

Near-infrared luminescence of manganate(V)-doped phosphates and vanadates

Abstract Manganese(V) is stabilized in various phosphate and vanadate lattices with apatite and spodiosite structure on quasi-tetrahedral sites. At all temperatures between 10 and 298 K the luminescence spectra consist of sharp lines in the near infrared, assigned to 1 E → 3 A 2 (T d ). The observed splitting Δ E between the two low-symmetry orbital components of the emitting state 1 E(T d ) is correlated with structural distortion data of the (PO 4 ) 3- and (VO 4 ) 3- tetrahedra in the host. Luminescence lifetimes of Mn 5+ in five different compounds vary between 300 and 700 μs at 10 K. At room-temperature lifetimes are reduced by factors of 1.4 to 11, depending on the host lattices.

Spectroscopy of CrO4-4, MnO3-4 and FeO2-4: New (3d)2 luminophores in the NIR

Abstract The (3d) 2 ions Cr 4+ , Mn 5+ and Fe 6+ show sharp-line luminescence in the NIR around 1.2, 1.2 and 1.6 μm, respectively. An attempt is made to find trends and similarities for these three ions and to provide an appropriate model.

Selective excitation of Ti2+Mn2+ and Mn2+Ti2+Mn2+ spin clusters in MgCl2

Ti2+Mn2+ dimers and three types of Mn2+Ti2+Mn2+ trimers obtained by codoping MgCl2 with Ti2+ and Mn2+ were studied by site‐selective dye‐laser spectroscopy. Very high selectivity was achieved by using the 6A1g→4A1g,4Eg excitation on Mn2+, which does not coincide with any Ti2+ single‐ion excitation. Sharp‐line 1Eg(T2g)→3Ta1g luminescence from Ti2+ was observed in the near infrared (NIR). Electronic ground‐state splittings resulting from Ti2+–Mn2+ exchange interactions were observed for the various spin clusters and, as a result, accurate exchange parameters could be obtained. The luminescence behavior of Ti2+Mn2+ pairs was investigated as a function of temperature and compared with the behavior of Ti2+ single ions in MgCl2. As in Ti2+:MgCl2 luminescence from Ti2+Mn2+ clusters was not only observed in the NIR but also in the visible, it corresponds to 3Tb1g→3Ta1g transitions.

Energy transfer in titanium (II) doped magnesium chloride

The low-temperature luminescence spectrum of MgCl 2 :0.05% Ti 2+ consists of a series of sharp lines in the near infrared (NIR). For higher Ti 2+ concentrations (0.2%, 2%, 5-10%) additional bands due to pairs and trimers of Ti 2+ are observed. In a crystal containing 2% Ti 2+ both luminescence spectra and decay curves give evidence for thermally activated non-radiative excitation energy transferf (ET) from single ions to pairs. A simplified model is fitted to the decay, it provides a quantitative estimate of the relevant transfer rates. It is found that only one out of three Ti 2+ single ions can act as an ET donor. This is in contrast to ruby, and the difference is due to the different dimensionalities of the two lattices

Site-selective spectroscopy of Ti2+V2+, Ti2+V2+V2+, Ti2+Ti2+V2+ and Ti2+Ti2+ spin clusters in magnesium chloride

Abstract At temperatures below 50 K magnesium chloride crystals simultaneously doped with Ti2+ and V2+ show broad-band luminescence from V2+ ions and sharp-line luminescence from Ti2+ ions and mixed Ti2+V2+ clusters in the near infrared. In addition to the known Ti2+ and V2+ absorption bands a double excitation of a Ti2+ and a neighbouring V2+ ion was observed in the green spectral range. Using tunable laser excitation in the range of 19 250–19 400 cm-1, exchange-coupled Ti2+−V2+ dimers, Ti2+−V2+−V2+ trimer chains and Ti2+Ti2+V2+ triangular trimers were studied selectively. From energy differences of luminescence lines the following parameters for antiferromagnetic exchange interactions were derived (using the bilinear Heisenberg operator H ex = -2J AB S A ·S A ): 2J TiV = -67 cm -1 in Ti2+−V2+ dimers, 2JVV = -41 cm-1 in Ti2+−V2+−V2+ chains and 2JTiTi = -101 cm-1 in Ti2+Ti2+V2+ triangles. Ti2+−Ti2+ dimers in MgCl2 crystals containing only Ti2+ ions can be excited selectively at 24 040 cm-1. For these species an exchange parameter of 2JTiTi = -109 cm-1 was found.