Lattice Expansion in Rb-Doped Hybrid Organic-Inorganic Perovskite Crystals Resulting in Smaller Band-Gap and Higher Light-Yield Scintillators.

Two-dimensional hybrid-organic-inorganic perovskite (2D-HOIP) lead bromide perovskite crystals have demonstrated great potential as scintillators with high light yields and fast decay times while also being low cost with solution-processable materials for wide energy radiation detection. Ion doping has been also shown to be a very promising avenue for improvements of the scintillation properties of 2D-HOIP crystals. In this paper, we discuss the effect of rubidium (Rb) doping on two previously reported 2D-HOIP single crystals, BA2PbBr4 and PEA2PbBr4. We observe that doping the perovskite crystals with Rb ions leads to an expansion of the crystal lattices of the materials, which also leads to narrowing of band gaps down to 84% of the pure compounds. Rb doping of BA2PbBr4 and PEA2PbBr4 shows a broadening in the photoluminescence and scintillation emissions of both perovskite crystals. Rb doping also leads to faster γ-ray scintillation decay times, as fast as 4.4 ns, with average decay time decreases of 15% and 8% for Rb-doped BA2PbBr4 and PEA2PbBr4, respectively, compared to those of undoped crystals. The inclusion of Rb ions also leads to a slightly longer afterglow, with residual scintillation still being below 1% after 5 s at 10 K, for both undoped and Rb-doped perovskite crystals. The light yield of both perovskites is significantly increased by Rb doping with improvements of 58% and 25% for BA2PbBr4 and PEA2PbBr4, respectively. This work shows that Rb doping leads to a significant enhancement of the 2D-HOIP crystal performance, which is of particular significance for high light yield and fast timing applications, such as photon counting or positron emission tomography.

Ligand-Mediated Revival of Degraded α-CsPbI3 to Stable Highly Luminescent Perovskite.

Although α-CsPbI3 is regarded as an attractive optical luminophore, it is readily degraded to the optically inactive δ-phase under ambient conditions. Here, we present a simple approach to revive degraded ("optically sick") α-CsPbI3 through "medication" with thiol-containing ligands. The effect of different types of thiols is systematically studied through optical spectroscopy. The structural reconstruction of degraded α-CsPbI3 nanocrystals to cubic crystals in the presence of thiol-containing ligands is visualized through high-resolution transmission electron microscopy and supported by X-ray diffraction analysis. We found that 1-dodecanethiol (DSH) effectively revives degraded CsPbI3 and results in high immunity towards moisture and oxygen, hitherto unreported. DSH facilitates the passivation of surface defects and etching of degraded Cs4 PbI6 phase, thus reverting them back to the cubic CsPbI3 phase, leading to enhanced PL and environmental stability.

Improvement of Light Output of MAPbBr3 Single Crystal for Ultrafast and Bright Cryogenic Scintillator.

The remarkable brightness and rapid scintillation observed in perovskite single crystals (SCs) become even more striking when they are operated at cryogenic temperatures. In this study, we present advancements in enhancing the scintillation properties of methylammonium lead bromide (MAPbBr3) SCs by optimizing the synthesis process. We successfully synthesized millimeter-sized MAPbBr3 SCs with bright green luminescence under UV light. However, both MAPbBr3 (Control-1M and THF-0.4M) SCs display notable radioluminescence exclusively at low temperatures due to their phase transitions. Notably, the THF-0.4M SCs exhibit a remarkable improvement in radioluminescence light yield, surpassing Control-1M SCs more than 2-fold. Further, THF-0.4M SCs demonstrate an ultrafast decay component of 0.52 ns (82.2%) and a slower component of 1.80 ns (17.8%), contributing to a rapid scintillation response at low temperatures. Therefore, the amalgamation of ultrafast decay components and improved radioluminescence light yield equips THF-0.4M SCs to emerge as a top choice for perovskite scintillators for X-ray timing applications.

Effect of Dual-Organic Cations on the Structure and Properties of 2D Hybrid Perovskites as Scintillators.

Two-dimensional (2D) hybrid organic-inorganic perovskite (HOIP) crystals show promise as scintillating materials for wide-energy radiation detection, outperforming their three-dimensional counterparts. In this study, we synthesized single crystals of (PEA2-xBZAx)PbBr4 (x ranging from 0.1 to 2), utilizing phenethylammonium (C6H5CH2CH2NH3+) and benzylammonium (C6H5CH2NH3+) cations. These materials exhibit favorable optical and scintillation properties, rendering them suitable for high light yield (LY) and fast-response scintillators. Our investigation, employing various techniques such as X-ray diffraction (XRD), photoluminescence (PL), time-resolved (TR) PL, Raman spectroscopy, radioluminescence (RL), thermoluminescence (TL), and scintillation measurements, unveiled lattice strain induced by dual-organic cations in powder X-ray diffraction. Density functional theory analysis demonstrated a maximal 0.13 eV increase in the band gap with the addition of BZA cation addition. Notably, the largest Stokes shift of 0.06 eV was observed in (BZA)2PbBr4. The dual-organic cation crystals displayed >80% fast component scintillation decay time, which is advantageous for the scintillating process. Furthermore, we observed a dual-organic cations-induced enhancement of electron-hole transfer efficiency by up to 60%, with a contribution of >70% to the fast component of scintillation decay. The crystal with the lowest BZA concentration, (PEA1.9BZA0.1)PbBr4, demonstrated the highest LYs of 14.9 ± 1.5 ph/keV at room temperature. Despite a 55-70% decrease in LY for BZA concentrations >5%, simultaneous reductions in scintillation decay time (12-32%) may work for time-of-flight positron emission tomography and photon-counting computed tomography. Our work underscores the crucial role of dual-organic cations in advancing our understanding of 2D-HOIP crystals for materials science and radiation detection applications.

Surface Engineering of Methylammonium Lead Bromide Perovskite Crystals for Enhanced X-ray Detection.

The surface quality of lead halide perovskite crystals can extremely influence their optoelectronic properties and device performance. Here, we report a surface engineering crystallization technique in which we in situ grow a polycrystalline methylammonium lead tribromide (MAPbBr3) film on top of bulk mm-sized single crystals. Such MAPbBr3 crystals with a MAPbBr3 passivating film display intense green emission under UV light. X-ray photoelectron spectroscopy demonstrates that these crystals with emissive surfaces are compositionally different from typical MAPbBr3 crystals that show no emission under UV light. Time-resolved photoluminescence and electrical measurements indicate that the MAPbBr3 film/MAPbBr3 crystals possess less surface defects compared to the bare MAPbBr3 crystals. Therefore, X-ray detectors fabricated using the surface-engineered MAPbBr3 crystals provide an almost 5 times improved sensitivity to X-rays and a more stable baseline drift with respect to the typical MAPbBr3 crystals.

Atomic-Scale Imaging and Nano-Scale Mapping of Cubic α-CsPbI3 Perovskite Nanocrystals for Inverted Perovskite Solar Cells.

Colloidal synthesized cubic α-CsPbI3 perovskite nanocrystals having a smaller lattice constant (a = 6.2315 Å) compared to the standard structure, and nanoscale mapping of their surfaces are reported to achieve superior photovoltaic performance under 45-55% humidity conditions. Atomic scale transmission electron microscopic images have been utilized to probe the precise arrangement of Cs, Pb, and I atoms in a unit cell of α-CsPbI3 NCs, which is well supported by the VESTA structure. Theoretical calculation using density functional theory of our experimental structure reveals the realization of direct band to band transition with a lower band gap, a higher absorption coefficient, and stronger covalent bonding between the Pb and I atoms in the [PbI6]4- octahedral, as compared to reported standard structure. Nanoscale surface mapping using Kelvin probe force microscopy yielding contact potential difference (CPD) and conductive atomic force microscopy for current mapping have been employed on α-CsPbI3 NCs films deposited on different DMSO doped PEDOT:PSS layers. The difference of CPD value under dark and light illumination suggests that the hole injection strongly depends on the interfaces with PEDOT:PSS layer. The carrier transport through grain interiors and grain boundaries in α-CsPbI3 probed by the single-point c-AFM measurements reveal the excellent photosensitivity under the light conditions. Finally, inverted perovskite solar cells, employing α-CsPbI3 NCs film as an absorber layer and PEDOT:PSS layer as a hole transport layer, have been optimized to achieve the highest power conversion efficiency of 10.6%, showing their potential for future earth abundant, low cost, and air stable inverted perovskite photovoltaic devices.

Outcome of humeral shaft fractures treated by functional cast brace.

BACKGROUND: Functional brace application for isolated humeral shaft fracture persistently yields good results. Nonunion though uncommon involves usually the proximal third shaft fractures. Instead of polyethylene bivalve functional brace four plaster sleeves wrapped and molded with little more proximal extension expected to prevent nonunion of proximal third fractures. Periodic compressibility of the cast is likely to yield a better result. This can be applied on the 1(st) day of the presentation as an outpatient basis. Comprehensive objective scoring system befitting for fracture humeral shaft is a need. MATERIALS AND METHODS: Sixty six (male = 40, female = 26) unilateral humeral shaft fractures of mean age 34.4 years (range 11-75 years) involving 38 left and 28 right hands were included in this study during April 2008 to December 2012. Fractures involved proximal (n = 18), mid (n = 35) and distal (n = 13) of humerus. Transverse, oblique, comminuted and spiral orientations in 18, 35 and 13 patients respectively. One had segmental fracture and three had a pathological fracture with cystic bone lesion. Mechanisms of injuries as identified in this study were road traffic accidents 57.6% (n = 38), fall 37.9% (n = 25). 12.1% (n = 8) had radial nerve palsy 7.6% (n = 5) had Type I open fracture. Four plaster strips of 12 layers and 5-7.5 cm broad depending on the girth of arm were prepared. Arm was then wrapped with single layer compressed cotton. Lateral and medial strips were applied and then after molding anterior and posterior strips were applied in such a way that permits full elbow range of motion and partial abduction of the shoulder. Care was taken to prevent adherence of one strip with other except in the proximal end. Limb was then put in loose collar and cuff sling intermittently allowing active motion of the elbow ROM and pendular movement of the shoulder. Weekly tightening of the cast by fresh layers of bandage over the existing cast brace continued. RESULTS: The results were assessed using 100 point scoring system where union allotted 30 points and 60 points allotted for angulations (10), elbow motion (10), shoulder abduction (10), shortening (5), rotation (5), absence of infection (10), absence of nerve palsy during treatment (10). Remaining 10 points were allotted for five items with two points each. They were the absence of skin sore, absence of vascular problem, absence of reflex sympathetic dystrophy (RSD), recovery of paralyzed nerve during injury and recovery of paralyzed nerve during treatment. Results were considered excellent with 90 and above, good with 80-89, fair with 70-79 and poor below 70 point. Results at 6 months were excellent in 43.94% (n = 29), good in 42.42% (n = 28), fair in 9.1% (n = 6), poor in 4.55% (n = 3). Union took place in 98.48% (n = 65) with an average of 10.3 weeks (range 6-16 weeks). 87.5% (n = 7) paralyzed radial nerve recovered. All wounds healed. Four patients had transient skin problem. One patient with mid shaft fracture had nonunion due to the muscle interposition. CONCLUSION: Modified functional cast brace is one of the options in treatment for humeral shaft fractures as it can be applied on the 1(st) day of the presentation in most of the situations. Simple objective scoring system was useful particularly in uneducated patients.