The organic-inorganic hybrid perovskites methylammonium lead iodide (CH3NH3PbI3) and the partially chlorine-substituted mixed halide CH3NH3PbI3-xClx emit strong and broad photoluminescence (PL) around their band gap energy of ∼1.6 eV. However, the nature of the radiative decay channels behind the observed emission and, in particular, the spectral broadening mechanisms are still unclear. Here we investigate these processes for high-quality vapor-deposited films of CH3NH3PbI3-xClx using time- and excitation-energy dependent photoluminescence spectroscopy. We show that the PL spectrum is homogenously broadened with a line width of 103 meV most likely as a consequence of phonon coupling effects. Further analysis reveals that defects or trap states play a minor role in radiative decay channels. In terms of possible lasing applications, the emission spectrum of the perovskite is sufficiently broad to have potential for amplification of light pulses below 100 fs pulse duration.

Homogeneous Emission Line Broadening in the Organo Lead Halide Perovskite CH3NH3PbI3-xClx.

The organic−inorganic hybrid perovskites methylammonium lead iodide (CH3NH3PbI3) and the partially chlorine-substituted mixed halide CH3NH3PbI3−xClx emit strong and broad photoluminescence (PL) around their band gap energy of ∼1.6 eV. However, the nature of the radiative decay channels behind the observed emission and, in particular, the spectral broadening mechanisms are still unclear. Here we investigate these processes for high-quality vapor-deposited films of CH3NH3PbI3−xClx using time- and excitation-energy dependent photoluminescence spectroscopy. We show that the PL spectrum is homogenously broadened with a line width of 103 meV most likely as a consequence of phonon coupling effects. Further analysis reveals that defects or trap states play a minor role in radiative decay channels. In terms of possible lasing applications, the emission spectrum of the perovskite is sufficiently broad to have potential for amplification of light pulses below 100 fs pulse duration.

https://www-herz.physics.ox.ac.uk/publications/Wehrenfennig14b.pdf

Homogeneous Emission Line Broadening in the Organo Lead Halide

The effects of deep trap population on the thermoluminescence of Al2O3:C

Experimental optical properties of lattice vacancy defects in single crystal α-Al 2 O 3 are reviewed. Specific ultraviolet absorption and luminescence bands are associated with F-type centers. Following extended exposures to epithermal neutron sources, photobleaching and anisotropic properties allowed the association of several of the visible and near infrared bands with F 2 -type centers. Photoconductivity, photostability and charge state considerations provided tentative placement of defect energy levels with respect to the conduction band edge.

Optical properties of lattice defects in α-Al2O3

Effect of high-dose irradiation on the optically stimulated luminescence of Al2O3:C.

In Mg- and Ca-doped α-Al2O3 crystals irradiated by X-rays at 80 K new paramagnetic colour centres are observed having an absorption band at about 255 nm and an emission band at 310 nm. The hyperfine structure of the EPR spectrum indicates that the unpaired electron spin interacts mainly with two Al27 nuclei. The optical and EPR spectra are consistent with the model of a centre involving one electron trapped at an anion vacancy adjoining the substitutional divalent ion (FMg or FCa). The luminescence band at 290 nm observed in the TSL peak at 225 K is suggested to result from the recombination of the holes with the FMg(FCa) centres.



[Russian Text Ignored]

Impurity-Associated Colour Centres in Mg- and Ca-Doped Al2O3 Single Crystals

Trap spectroscopy and tunnelling luminescence in feldspars

Photo- and thermostimulated processes in α-Al2O3

The luminescence under X-ray excitation (XL) and the thermostimulated luminescence (TSL) in Al2O3 crystals are studied in the spectral region 2 to 6 eV at temperatures between 80 and 700 K. In crystals treated in reducing atmospheres at high temperatures a luminescence band at 3.0 eV is dominating the XL and TSL spectra. This band is also observed in spectra of neutron-irradiated crystals together with bands at 3.75 and 2.4 eV. In Mg-doped crystals a number of bands are observed peaking at 3.15, 3.75, 4.0, 4.4., and 4.75 eV. The luminescence band at 3.75 eV can be due to F+ centres. The band at 3.0 eV is connected with some donor type defects. In all the crystals studied (except the untreated one) one or both of the main TSL peaks at 225 and 260 K are observed. The first one is ascribed to release of holes, the other to electron release from some donor centres.



[Russian Text Ignored].

Recombination luminescence in single crystal Al2O3

The origin of the luminescence bands at 7.5 eV anv 3.8 eV appearing additionaly to the luminescence of F- and F+- centres in pure Al2O3 are investigated. The time - resolved luminescence spectra, absorption and luminescence excitation spectra as well as trap spectroscopy data depending on deviation from the stochiometry of crystals are discussed in terms of self - trapping of excitons in two configurations. The role of defects due to annihilation of excitons is considered.

Defect assisted intrinsic luminescence in Al2O3 crystals

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