LUX-ZEPLIN

Abstract:

Luminescence probes that facilitate multimodal non-contact measurements of temperature are of particular interest due to the possibility of cross-referencing results across different readout techniques. This intrinsic referencing is an essential addition that enhances accuracy and reliability of the technique. A further enhancement of sensor performance can be achieved by using two luminescent ions acting as independent emitters, thereby adding in-built redundancy to non-contact temperature sensing, using a single readout technique. In this study we combine both approaches by engineering a material with two luminescent ions that can be independently probed through different readout modes of non-contact temperature sensing. The approach was tested using Al2O3 co-doped with Cr3+ and Mn4+, exhibiting sharp emission lines due to 2E → 4A2 transitions. The temperature sensing performance was examined by measuring three characteristics: temperature-induced changes of the intensity ratio of the emission lines, their spectral position, and the luminescence decay time constant. The processes responsible for the changes with temperature of the measured luminescence characteristics are discussed in terms of relevant models. By comparing temperature resolutions achievable by different modes of temperature sensing it is established that in Al2O3-Cr,Mn spectroscopic methods provide the best measurement accuracy over a broad temperature range. A temperature resolution better than ±2.8 K can be achieved by monitoring the luminescence intensity ratio (40–145 K) and the spectral shift of the R-line of Mn4+ (145–300 K range).

Abstract:

Metal-halide perovskite semiconductors have attracted intensive interest in the last decade, particularly for applications in photovoltaics. Low-energy optical phonons combined with significant crystal anharmonicity play an important role in charge-carrier cooling and scattering in these materials, strongly affecting their optoelectronic properties. We have observed optical phonons associated with Pb—I stretching in both MAPbI3 single crystals and polycrystalline thin films as a function of temperature by measuring their terahertz (THz) conductivity spectra with and without photoexcitation. An anomalous bond hardening was observed under above-bandgap illumination for both single-crystal and polycrystalline MAPbI3. First-principles calculations reproduced this photo-induced bond hardening and identified a related lattice contraction (photostriction), with the mechanism revealed as Pauli blocking. For single-crystal MAPbI3, phonon lifetimes were significantly longer and phonon frequencies shifted less with temperature, compared with polycrystalline MAPbI3. We attribute these differences to increased crystalline disorder, associated with grain boundaries and strain in the polycrystalline MAPbI3. Thus we provide fundamental insight into the photoexcitation and electron–phonon coupling in MAPbI3.

Abstract:

Applications that utilize scintillation detectors at low temperatures are growing in number. Many of these require materials with high light yield and a fast response. Here we report on the low-temperature characterisation of ZnSe doped with Al or Te, respectively. The X-ray luminescence and decay curves were measured over the 77–295 K temperature range, and alpha particle excitation was used to examine scintillation light output and decay kinetics over the range 9–295 K. A significant improvement of the scintillation characteristics was observed at cooling below 100 K. The scintillation light yield of the crystals increases by a factor about two, and the decay time constant decreases by almost an order of magnitude to 0.3–0.4 μs. These improvements enhance the potential of ZnSe-based crystals for application in cryogenic scintillation detectors of ionising radiation.