Hans-Ulrich Güdel

Application of NaYF4:Er3+ up-converting phosphors for enhanced near-infrared silicon solar cell response

Erbium-doped sodium yttrium fluoride (NaYF4:Er3+) up-conversion phosphors were attached to the rear of a bifacial silicon solar cell to enhance its reponsivity in the near-infrared. The incident wavelength and light intensity were varied and the resulting short circuit current of the solar cell was measured. A close match between the spectral features of the external quantum efficiency and the phosphor absorption is consistent with the energy transfer up-conversion process. The peak external quantum efficiency of the silicon solar cell was measured to be (2.5±0.2)% under 5.1 mW laser excitation at 1523 nm, corresponding to an internal quantum efficiency of 3.8%.

High-energy-resolution scintillator: Ce3+ activated LaBr3

The scintillation properties of LaCl3 doped with 10% Ce3+ are presented. Under optical and gamma ray excitation, Ce3+ emission is observed to peak at 330 and 352 nm. The scintillation light output is 46 000±1000 photons/MeV at 662 keV. Forty percent is emitted with a decay time of 26 ns, 30% with 210 ns, and 30% with about 1000 ns. An energy resolution (full width at half maximum over the peak position) of 3.3±0.3% was observed for the 662 keV full absorption peak.

Bose–Einstein condensation of the triplet states in the magnetic insulator TlCuCl3

Bose–Einstein condensation denotes the formation of a collective quantum ground state of identical particles with integer spin or intrinsic angular momentum. In magnetic insulators, the magnetic properties are due to the unpaired shell electrons that have half-integer spin. However, in some such compounds (KCuCl3 and TlCuCl3), two Cu2+ ions are antiferromagnetically coupled to form a dimer in a crystalline network: the dimer ground state is a spin singlet (total spin zero), separated by an energy gap from the excited triplet state (total spin one). In these dimer compounds, Bose–Einstein condensation becomes theoretically possible. At a critical external magnetic field, the energy of one of the Zeeman split triplet components (a type of boson) intersects the ground-state singlet, resulting in long-range magnetic order; this transition represents a quantum critical point at which Bose–Einstein condensation occurs. Here we report an experimental investigation of the excitation spectrum in such a field-induced magnetically ordered state, using inelastic neutron scattering measurements of TlCuCl3 single crystals. We verify unambiguously the theoretically predicted gapless Goldstone mode characteristic of the Bose–Einstein condensation of the triplet states.

Efficient visible to infrared quantum cutting through downconversion with the Er3+–Yb3+ couple in Cs3Y2Br9

Downconversion of one visible photon to two near-infrared photons may increase the efficiency of c-Si solar cells by 30%. The lanthanide ion couple Er3+–Yb3+ is well known for efficient upconversion but for the reverse process, downconversion, fast multiphonon relaxation from the F47/2 level has been shown to compete with downconversion. Here we report efficient downconversion for the Er–Yb couple in Cs3Y2Br9. The low phonon energy in this bromide host suppresses multiphonon relaxation and efficient two step energy transfer from the F47/2 level of Er3+ is observed and results in strong 1000 nm emission from Yb3+. Based on emission spectra and luminescence life time measurements an intrinsic downconversion efficiency close to 200% is determined.

Low-Energy Magnetic Excitations of the Mn 12 -Acetate Spin Cluster Observed by Neutron Scattering

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Development and characterization of highly efficient new cerium doped rare earth halide scintillator materials

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Quantum magnets under pressure: controlling elementary excitations in TlCuCl3.

-acetate by inelastic neutron scattering and diffraction. We separated the energy levels corresponding to the splitting of the lowest

Scintillation properties of LaCl/sub 3/:Ce/sup 3+/ crystals: fast, efficient, and high-energy resolution scintillators

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Low-temperature upconversion spectroscopy of nanosized Y2O3:Er,Yb phosphor

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Energy resolution of some new inorganic-scintillator gamma-ray detectors

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