Influence of gold nanoparticles on the nonlinear optical and photoluminescence properties of Eu2O3 doped alkali borate glasses.

Alkali borate glasses activated with trivalent europium ions and rooted with gold (Au) nanoparticles (NPs) were synthesised through a melt quenching process involving a selective thermochemical reduction and their applicability as photonic materials was assessed in detail. Non-linear optical (NLO) measurements were performed using a Z-scan approach in the wavelength range of 700-1000 nm. The open aperture Z-scan signatures for the Eu3+-containing glasses embedded with and without the Au NPs established a reverse saturable absorption (RSA) at all of the studied wavelengths ascribed to the two-photon absorption (2PA). Surprisingly, the nonlinear optical absorption switched to a saturable absorption (SA) with an increase in the concentration of AuCl3. With the incorporation of the Au NPs, the UV excited photoluminescence (PL) intensity of the Eu3+-doped glasses increased first as a consequence of the local field enhancement by the Au NPs, and subsequently decreased at a higher concentration of AuCl3 due to the reverse energy transfer from the Eu3+ ion to the Au0 NPs. The electronic polarization effect of the host glass enhanced the 5D0→7F4 transition intensity on the incorporation of the gold NPs owing to the gold NP-embedded glasses showing a deep-red emission. The NLO and PL studies suggested that the investigated glasses containing a 0.01 mol% of AuCl3 is practically appropriate for photonic applications.

Broadband ultrafast nonlinear optical studies revealing exciting multi-photon absorption coefficients in phase pure zero-dimensional Cs4PbBr6 perovskite films.

Lead halide perovskite nanocrystals (NCs) apart from their overwhelming optoelectronic applications have recently demonstrated promising nonlinear optical (NLO) properties such as strong two-photon absorption cross-sections (∼105 GM), two-photon fluorescence, and saturable absorption even at very high peak intensity. Zero-dimensional perovskite-related materials (0-D PRMs) are a new class of materials offering a high exciton binding energy (Eg ≥ 180 meV) with a strong photoluminescence (PL) quantum yield in few cases. Herein, we report the broadband third-order NLO properties of phase pure Cs4PbBr6 0-D PRM achieved using the Z-scan and degenerate four-wave mixing techniques in the femtosecond regime. Considering the growing content of the fluorescent and non-fluorescent forms of this material, we have performed our studies on both of them. These perovskite NCs exhibited strong multi-photon absorption properties in the near-infrared region with two-photon absorption (2PA) (cross-section, σ2 = 10-43-10-44 cm4 s equivalent to ∼106 GM) in the 500-800 nm region, three-photon absorption (3PA) (cross-section, σ3 ∼10-73 cm6 s2) in the 900-1200 nm region and four-photon absorption (4PA) (cross-section, σ4 ∼10-100 cm8 s3) in the 1300-1500 nm spectral region. These multi-photon absorption processes are explained using a simple band diagram. The measured NLO coefficients and cross-sections are fairly large when compared to some of the earlier reports on perovskite-based NCs. Cs4PbBr6 0-D PRM also demonstrated a large third-order NLO susceptibility χ(3) (∼10-7 esu), which can be attributed to the strong quantum confinement arising from spatially isolated, exciton containing individual [PbBr6]4- octahedron. These results clearly suggest the potential of 0D-PRMs in applications such as photonics and ultrafast all-optical switching devices.

Comparative study of psychiatric morbidity among the displaced and non-displaced populations in the Andaman and Nicobar Islands following the tsunami.

OBJECTIVE: The objective of this study was to compare the psychiatric morbidity between the displaced and non-displaced populations of the Andaman and Nicobar Islands during the first three months following the 2004 earthquake and tsunami. METHODS: The study was conducted at the 74 relief camps in the Andaman and Nicobar Islands. Port Blair had 12 camps, which provided shelter to 4,684 displaced survivors. There were 62 camps on Car-Nicobar Island, which provided shelter to approximately 8,100 survivors who continued to stay in their habitat (non-displaced population). The study sample included all of the survivors who sought mental health assistance inside the camp. A psychiatrist diagnosed the patients using the ICD-10 criteria. RESULTS: Psychiatric morbidity was 5.2% in the displaced population and 2.8% in the non-displaced population. The overall psychiatric morbidity was 3.7%. The displaced survivors had significantly higher psychiatric morbidity than did the non-displaced population. The disorders included panic disorder, anxiety disorders not otherwise specified, and somatic complaints. The existence of an adjustment disorder was significantly higher in the non-displaced survivors. Depression and post-traumatic stress disorder (PTSD) were distributed equally in both groups. CONCLUSIONS: Psychiatric morbidity was found to be highest in the displaced population. However, the incidence of depression and PTSD were distributed equally in both groups. Involvement of community leaders and survivors in shared decision-making processes and culturally acceptable interventions improved the community participation. Cohesive community, family systems, social support, altruistic behavior of the community leaders, and religious faith and spirituality were factors that helped survivors cope during the early phase of the disaster.