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Defects have always been an integral part of semiconductor crystals, controlling their optical and electronic properties. Even though growing popularity of the CsPbX 3 (X = Cl, Br, I, and their mixture) nanocrystals (NCs) in various applications stems from their defect-tolerant nature, the properties, stability, and practical utility of these substances are still very much governed by the defects. A variety of methods, which are halide-specific, have been developed to regulate the activities of the defects for enhancing the photoluminescence and stability of these NCs. In this Perspective, we trace the origin and manifestation of different types of defects in photoluminescence properties and stability of the CsPbX 3 NCs, critically examine the rationale of various passivation strategies to obtain an in-depth understanding of the problem, and recommend the most effective strategy to be followed for tackling defects under any given condition.

To obtain an in-depth understanding of the dynamics and mechanism of carrier recombination in CsPbBr 3 nanocrystals (NCs), we have investigated the photoluminescence (PL) of this material at the single-particle level using the time-tagged−time-resolved method. The study reveals two distinct types of PL fluctuations of the NCs, which are assigned to flickering and blinking. The flickering is found to be due to excess surface trap on the NCs, and the flickering single particles are transformed into blinking ones with significant enhancement of PL intensity and stability on postsynthetic surface treatment. Intensitycorrelated lifetime analysis of the PL time trace reveals both trapmediated nonradiative band-edge carrier recombination and positive trion recombination in single NCs. Dynamical and statistical analysis suggests a diffusive nature of the trap states to be responsible for the PL intermittency of the system. These findings throw light on the nature of the trap states, reveal the manifestation of these trap states in PL fluctuation, and provide an effective way to control the dynamics of CsPbBr 3 NCs.

Exploration of the full potential of the perovskite nanocrystals (NCs) for different applications requires a thorough understanding of the pathways of recombination of the photogenerated charge carriers and associated dynamics. In this work, we have tracked the recombination routes of the charge carriers by probing photoluminescence (PL) intermittency of the immobilized and freely diffusing single CsPbBr3 NCs employing a time-tagged-time-resolved method. The immobilized single CsPbBr3 NCs show a complex PL time-trace, a careful analysis of which reveals that nonradiative band-edge recombination through trap states, trion recombination, and trapping of the hot carriers contribute to the blinking behavior of any given NC. A drastically suppressed PL blinking observed for the NCs treated with a tetrafluoroborate salt indicates elimination of most of the undesired recombination processes. A fluorescence correlation spectroscopy (FCS) study on the freely diffusing single NCs shows that enhanced PL and suppressed blinking of the treated particles are the outcome of an increase in per-particle brightness, not due to any increase in the number of particles undergoing “off”–“on” transition in the observation volume. The mechanistic details obtained from this study on the origin of blinking in CsPbBr3 NCs provide deep insight into the radiative and nonradiative charge carrier recombination pathways in these important materials, and this knowledge is expected to be useful for better design and development of bright photoluminescent samples of this class for optoelectronic applications.

Pegylated interferon-α (PEG-IFN-α) is a first line option in the treatment of chronic hepatitis B. Compared with nucleos(t)ide analogues (NAs), therapy with PEG-IFN-α has the advantages of finite treatment duration and higher rates of hepatitis B surface antigen (HBsAg) and hepatitis B e antigen (HBeAg) seroconversion, but the disadvantage of greater adverse effects. Choosing PEG-IFN-α requires careful evaluation of the likelihood of achieving a sustained off-treatment response. Sustained off-treatment response with PEG-IFN-α can be predicted by baseline factors in HBeAg positive disease. These include genotype A or B, low viral load, high alanine aminotransferase (ALT), older age and female gender. On the other hand, no pre-treatment factors have been identified that can reliably predict response in HBeAg negative disease. Using on-treatment quantitative HBsAg levels, failure of a long term response can be identified with high negative predictive value (NPV). However, no combination of on treatment parameters have been identified so far that can precisely forecast successful treatment. Up until recently, there was little evidence supporting the use of combining PEG-IFN with NAs. The addition of PEG-IFN in patients who already have viral suppression with NAs therapy appears superior to continuing NAs alone in achieving a sustained response. Also, tenofovir disoproxil fumarate (TDF) in combination with PEG-IFN has been reported to enable significantly higher HBsAg loss than with either monotherapy alone. This occurred in both HBeAg positive and negative patients across all genotypes. In spite of recent developments, rates of HBsAg loss are still only in the order of 10% and so cure remains elusive. Further research is required to identify the optimal combination or sequential therapy regimen, and the subgroups with the highest rates of response so that they can be targeted.

a Ph.D. student under Prof. Anunay Samanta. His research interest is the synthesis and understanding of ultrafast photoinduced processes of highly luminescent perovskite nanocrystals.Sumanta Paul, after completing his Master's degree from the School of Chemistry, University of Hyderabad, in 2017, is working on his Ph.D. under the supervision of Prof. Anunay Samanta. His research focuses on the synthesis and study of photophysical properties of perovskite nanocrystals at the bulk and single-particle levels.

Background: Extreme hyperbilirubinemia leading to neurologic disability and death is disproportionately high in low to middle income countries (LMIC) such as Bangladesh, and is largely preventable through timely treatment. Of the estimated 50% of newborns born in LMICs born at home, few receive screening or treatment for hyperbilirubinemia, leading to 6 million newborns per year who need phototherapy treatment for hyperbilirubinemia but are untreated. Household screening and treatment for neonatal hyperbilirubinemia with phototherapy administered by a trained community health worker (CHW) may increase indicated treatment for neonatal hyperbilirubinemia in comparison to the existing care system in Bangladesh. Methods: 530 Bangladeshi women in their 2nd or 3rd trimester of pregnancy from the rural community of Sakhipur, Bangladesh will be recruited for a cluster randomized trial and randomized to the intervention arm — home screening and treatment for neonatal hyperbilirubinemia — or the comparison arm to receive usual care. In the intervention arm, CHWs will provide mothers with two prenatal visits, visit newborns by 2 days of age and then daily for 3 days to measure transcutaneous bilirubin (TcB) and monitor clinical danger signs. Newborns without danger signs but with a TcB above the treatment threshold <15 mg/dL will be treated with light-emitting diode (LED) phototherapy at home. Newborns with danger signs or TcB >15 mg/dL will be referred to a hospital for treatment. Treatment rates for neonatal hyperbilirubinemia in each arm will be compared. Conclusion: This study will evaluate the effectiveness of CHW-led home phototherapy to increase neonatal hyperbilirubinemia treatment rates in rural Bangladesh. LMICs are expanding access to postnatal care by using CHWs, and our work will give CHWs a curative treatment option for neonatal hyperbilirubinemia. Similar projects in other LMICs can be pursued to dramatically extend healthcare access to vulnerable newborns with hyperbilirubinemia.

Highly luminescent cesium lead halide (CsPbX 3 , X = Cl, Br, I) perovskite nanocrystals (NCs) are promising materials for a number of optoelectronic applications like LEDs and other display technologies. However, low photoluminescence (PL) quantum yield (QY) of the large-bandgap violet-and blue-emitting CsPbCl 3 and CsPb(Cl/Br) 3 NCs is an obstacle to the development of blue-and white-emitting LEDs. In this work, we show that these NCs with high PLQY can be obtained directly by employing an appropriate halide precursor and by optimizing the Pb:X precursor ratio. Specifically, employing N-chloro-and Nbromophthalimides as halide precursors and varying the Pb:X precursor ratio, we have obtained stable and highly luminescent (PLQY 80−99%) perovskite NCs emitting in the blue-violet region extending to green by direct synthesis. Time-resolved PL and ultrafast pump−probe studies of these systems reveal the effect of Pb:X precursor ratio on the carrier recombination processes. Rapid carrier trapping is found to be the dominant process that impairs the PLQY of the NCs obtained by using a stoichiometric (1:3) Pb:X precursor ratio. This trapping of carriers is effectively alleviated by using an excess amount of the halide precursor during the preparation of the NCs. The results brighten the potential utility of these high-quality perovskite NCs emitting in the blue-violet region in optical applications.