Performance of ZnSe-based scintillators at low temperatures
JOURNAL OF LUMINESCENCE 239 (2021) ARTN 118360
Al2O3 co-doped with Cr3+ and Mn4+, a dual-emitter probe for multimodal non-contact luminescence thermometry.
Dalton transactions (Cambridge, England : 2003) (2021)
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).Ultrafast photo-induced phonon hardening due to Pauli blocking in MAPbI3 single-crystal and polycrystalline perovskites
Journal of Physics: Materials IOP Publishing 4:4 (2021) 044017
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.Limits to electrical mobility in lead-halide perovskite semiconductors
Journal of Physical Chemistry Letters American Chemical Society 12:14 (2021) 3607-3617
Abstract:
Semiconducting polycrystalline thin films are cheap to produce and can be deposited on flexible substrates, yet high-performance electronic devices usually utilize single-crystal semiconductors, owing to their superior charge-carrier mobilities and longer diffusion lengths. Here we show that the electrical performance of polycrystalline films of metal-halide perovskites (MHPs) approaches that of single crystals at room temperature. Combining temperature-dependent terahertz conductivity measurements and ab initio calculations we uncover a complete picture of the origins of charge-carrier scattering in single crystals and polycrystalline films of CH3NH3PbI3. We show that Fröhlich scattering of charge carriers with multiple phonon modes is the dominant mechanism limiting mobility, with grain-boundary scattering further reducing mobility in polycrystalline films. We reconcile the large discrepancy in charge-carrier diffusion lengths between single crystals and films by considering photon reabsorption. Thus, polycrystalline films of MHPs offer great promise for devices beyond solar cells, including light-emitting diodes and modulators.Simulations of events for the LUX-ZEPLIN (LZ) dark matter experiment
ASTROPARTICLE PHYSICS 125 (2021) ARTN 102480