Color tunable Tb3+ doped SrGd2Al2O7 nanophosphor is synthesized employing a facile and economic urea assisted solution combustion approach. XRD studies confirm the crystallization of single phased ...SrGd2(1-x)Tb2xAl2O7 nanophosphor in tetragonal lattice with I4/mmm (139) space group. Rietveld refinement is performed over SrGd1.9Tb0.1Al2O7 sample to execute qualitative as well as quantitative phase analysis. TEM analysis confirms the more or less spherical shaped phosphors in nano domain with average particle size ranging 45–80 nm. Photoluminescent investigation reveals that this nanophosphor can be successfully excited by ultraviolet light yielding significant luminescent properties arising due to radiative transitions from 5D3,4 levels to 7Fj levels. Dipole-dipole interactions are solely responsible for the energy transfer causing concentration quenching. Concentration controlled luminescent tendency can be employed to induce chromaticity from blue to green region. Findings of the study proclaim the application of this nanophosphor as one of the green component of tricolor based ultraviolet excited white LEDs.
A white light emitting Barium gadolinium vanadate, Ba2GdV3O11:Eu3+, is developed using time-saving combustion synthesis technique. The Rietveld analysis of the optimum luminescent composition ...(Ba2Gd0.97V3O11:0.03Eu3+) confirmed that it crystallizes into the monoclinic system with P21/a space group. The calculation of lattice parameters unveiled the unit cell expansion which in turn governed the asymmetry around activator. The photoluminescent analysis showed an efficient energy transfer from vanadate absorption of Ba2GdV3O11 host to Eu3+, resulting in a very intense characteristic emission of the Eu3+. The PL decay investigations of Ba2GdV3O11:0.03Eu3+ nanophosphor gave the radiative lifetime and total spontaneous emission probabilities. Judd-Ofelt parameterization provided the refractive index of the host and stimulated emission cross section for 5D0?7F4 (8.03) transition in Ba2GdV3O11:0.03Eu3+ phosphor. The quantum efficiency of 5D0 state in Ba2Gd0.97Eu0.03V3O11 phosphor was calculated to be 79%, resulting in a pure white emission. All results demonstrate that Ba2Gd0.97V3O11:0.03Eu3+ is a potential candidate for single-phased WLEDs.
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•Ba2GdV3O11:Eu3+ nanocrystals were synthesized via combustion method.•Lattice parameters of optimum fluorescent composition were calculated.•Band-gap was calculated for both the host and doped sample.•Quantum efficiency and peak stimulated emission cross-sections have been determined.•Potential candidate for solid state lighting, and display devices.
Single-phased bright-red emitter Ca9Bi1–x(PO4)7:xEu3+ nanophosphor series was obtained by time-saving combustion-synthesis technique. The structural prototype for Ca9Bi(PO4)7 and ...Ca9Bi0.40(PO4)7:0.60Eu3+ were obtained by using the Rietveld refinement method, revealing a trigonal crystal system of R3c(161) space group symmetry. The values of the band-gap for maximum-fluorescent-concentration and pure host were determined to be 4.23 and 4.30 eV, respectively. The critical distance for energy migration (12.35 Å) and Dexter's exchange-profiling held the dipole/dipole (d–d) interactions responsible for the quenching process observed after optimum composition. The refractive index of the pure host (2.22) and the photoluminescent (PL) emission spectra of Eu3+-doped samples were used to work out Judd-Ofelt intensity parameters. The detailed photo-luminescent analysis provided the value of quantum efficiency, non-radiative and total radiative transition-rate for Ca9Bi0.40(PO4)7:0.60Eu3+ phosphor. Furthermore, various optical results, including the very high value of stimulated emission-cross-section (10.64), claim Ca9Bi0.40(PO4)7:0.60Eu3+ system as a very much promising candidate for the laser and solid-state lighting (SSL) devices.
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•Ca9Bi(PO4)7:Eu3+ phosphors are synthesized first time via solution combustion route.•Lattice parameters are determined for both the host and doped sample.•Lattice sites of Eu3+/Bi3+ and Judd-Ofelt parameters are obtained.•Quantum efficiency and peak stimulated emission cross-sections have been calculated.•Potential candidates for solid state lighting, display and laser devices.
With the emergence of newer SARS-CoV-2 variants and their substantial effects on the levels and duration of protection against infection, an understanding of these characteristics of the protection ...conferred by humoral and cellular immunity can aid in the proper development and implementation of vaccine and safety guidelines.
We conducted a rapid literature review and searched five electronic databases weekly from 1 November 2021 to 30 September 2022. Studies that assessed the humoral or cellular immunity conferred by infection, vaccination or a hybrid (combination of both) in adults and risk groups (immunocompromised and older populations) were identified. Studies were eligible when they reported data on immunological assays of COVID-19 (related to vaccination and/or infection) or the effectiveness of protection (related to the effectiveness of vaccination and/or infection).
We screened 5103 studies and included 205 studies, of which 70 provided data on the duration of protection against SARS-CoV-2 infection. The duration of protection of adaptive immunity was greatly impacted by Omicron and its subvariants: levels of protection were low by 3-6 months from exposure to infection/vaccination. Although more durable, cellular immunity also showed signs of waning by 6 months. First and second mRNA vaccine booster doses increased the levels of protection against infection and severe disease from Omicron and its subvariants but continued to demonstrate a high degree of waning over time.
All humoral immunities (infection-acquired, vaccine-acquired and hybrid) waned by 3-6 months. Cellular immunity was more durable but showed signs of waning by 6 months. Hybrid immunity had the highest magnitude of protection against SARS-CoV-2 infection. Boosting may be recommended as early as 3-4 months after the last dose, especially in risk groups.
Nano-scaled green-emitting Ba
3
Bi
2
(PO
4
)
4
:Tb
3+
crystalline series was effectively obtained via very efficient and straightforward combustion-synthesis route for the very first time. The JCPDS ...data (Card No: 780204) of Ba
3
Bi
2
(PO
4
)
4
crystal were used for profiling the diffraction patterns of various mol% samples. The structure and lattice parameters of Ba
3
Bi
1.70
Tb
0.30
(PO
4
)
4
system have been investigated by Rietveld refinement analysis. Further, it was found that incorporation of dopant (Tb
3+
) ion into the monoclinic crystal lattice of
C12/c1
(15) space group symmetry did not induce any major structural changes. Lowering in the optical band-gap value from 4.16 to 4.02 eV was observed when Ba
3
Bi
2
(PO
4
)
4
host lattice is doped with 15 mol% of activator ions. The photoluminescence analysis of Ba
3
Bi
2
(PO
4
)
4
:Tb
3+
series at 368 nm excitation yielded the bright green emission due to the
5
D
4
→
7
F
5
transition. A maximum in emission intensity is observed corresponding to the Ba
3
Bi
1.70
Tb
0.30
(PO
4
)
4
composition. Critical energy distance (13.235 Å) proposed the existence of energy transfer through multipolar interaction (dipole–dipole) phenomenon, which is cross-verified by Huang analysis (
s
= 4.94). The value of radiative-lifetime and non-radiative transition rate are calculated to be 2.22 ms and 10.3 s
−1
, respectively. Furthermore, the very high value of quantum efficiency (97%) and the results of various optical analysis favor the practical utility of down-conversion Ba
3
Bi
1.70
Tb
0.30
(PO
4
)
4
nanophosphor for solid-state and other illuminating devices.
Guaranteeing durability, provenance, accessibility, and trust in open data sets can be challenging for researchers and organizations that rely on public repositories of data critical for epidemiology ...and other health analytics. The required data repositories are often difficult to locate and may require conversion to a standard data format. Data-hosting websites may also change or become unavailable without warning. A single change to the rules in one repository can hinder updating a public dashboard reliant on data pulled from external sources. These concerns are particularly challenging at the international level, because policies on systems aimed at harmonizing health and related data are typically dictated by national governments to serve their individual needs.
In this paper, we introduce a comprehensive public health data platform, EpiGraphHub, that aims to provide a single interoperable repository for open health and related data.
The platform, curated by the international research community, allows secure local integration of sensitive data while facilitating the development of data-driven applications and reports for decision-makers. Its main components include centrally managed databases with fine-grained access control to data, fully automated and documented data collection and transformation, and a powerful web-based data exploration and visualization tool.
EpiGraphHub is already being used for hosting a growing collection of open data sets and for automating epidemiological analyses based on them. The project has also released an open-source software library with the analytical methods used in the platform.
The platform is fully open source and open to external users. It is in active development with the goal of maximizing its value for large-scale public health studies.
•Morbidity and mortality in children due to COVID-19 remained low•Adolescents had higher reported cases than younger children•Reported cases were lower in pediatric population than adult ...population•Testing protocols vary between countries; reflects bias in reported cases
Few data on the COVID-19 epidemiological characteristics among the pediatric population in Africa exists. This paper examines the age and sex distribution of the morbidity and mortality rate in children with COVID-19 and compares it to the adult population in 15 Sub-Saharan African countries.
A merge line listing dataset shared by countries within the Regional Office for Africa was analyzed. Patients diagnosed within 1 March and 1 September 2020 with a confirmed positive RT-PCR test for SARS-CoV-2 were analyzed. Children's data were stratified into three age groups: 0-4 years, 5-11 years, and 12-17 years, while adults were combined. The cumulative incidence of cases, its medians, and 95% confidence intervals were calculated.
9% of the total confirmed cases and 2.4% of the reported deaths were pediatric cases. The 12-17 age group in all 15 countries showed the highest cumulative incidence proportion in children. Adults had a higher case incidence per 100,000 people than children.
The cases and deaths within the children's population were smaller than the adult population. These differences may reflect biases in COVID-19 testing protocols and reporting implemented by countries, highlighting the need for more extensive investigation and focus on the effects of COVID-19 in children.
High-brightness, red-emitting Ca9Gd1−x(PO4)7:xEu3+ phosphors were developed via the facile route of solution-combustion. The Rietveld-assisted structural analysis of Ca9Gd(PO4)7 and ...Ca9Gd0.40Eu0.60(PO4)7 systems unveiled a trigonal crystal system having R3c(161) space-group symmetry. The absence of JCPDS data was compensated by simulating one from refined structural prototype. The band-gap for the host and best luminescent composition were determined to be 4.55 and 4.01 eV, respectively. The ratio of Judd-Ofelt parameters inferred a very high asymmetry around activator ion which can further be enhanced as a function of dopant concentration. The refractive index of Ca9Gd(PO4)7 was determined to be 2.34. The value of stimulated emission cross section, total radiative transition rate and non-radiative transition rate for Ca9Gd0.40Eu0.60(PO4)7 are calculated from detailed photo-luminescent (PL) analysis. Furthermore, very high value of quantum efficiency (98.13%) and radiative lifetime (1.85 ms) suggested that Ca9Gd0.40Eu0.60(PO4)7 nanophosphor have practical applicability in PC-WLEDs (components of solid-state lighting).
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•Solution grown LNO crystals showed sharp violet emission peak at 438nm.•Wide band gap and low Urbach energy was found in UV absorption spectra.•Low dielectric constant along with ...phase change transition at 33°C was found.•A saturated hysteresis loop and piezoelectricity (d33 &g33) was observed.•The SHG efficiency was found to be 1.2times that of KDP.
New semiorganic nonlinear optical single crystals of Lithium nitrate oxalate monohydrate (LNO) were grown by slow evaporation solution technique. Single crystal X-ray diffraction study indicated that LNO crystal belongs to the triclinic system with space group P1. Various functional groups present in the material were identified by FTIR and Raman analysis. UV–vis study showed the high transparency of crystals with a wide band gap 5.01eV. Various Optical constants i.e. Urbach energy (Eu), extinction coefficient (K), refractive index, optical conductivity, electric susceptibility with real and imaginary parts of dielectric constant were calculated using the transmittance data which have applications in optoelectronic devices. A sharp emission peak was found at 438nm in photoluminescence measurement, which revealed suitability of crystal for fabricating violet lasers. In dielectric studies, a peak has been observed at 33°C which is due to ferroelectric to paraelectric phase transition. Piezoelectric charge coefficients (d33=9.2pC/N and g33) have been calculated, which make it a suitable for piezoelectric devices applications. In ferroelectric studies, a saturated loop was found in which the values of coercive field and remnant polarization were found to be 2.18kV/cm and 0.39μC/cm2, respectively. Thermal behavior was studied by TGA and DSC studies. The relative SHG efficiency of LNO was found to be 1.2times that of KDP crystal. In microhardness study, Meyer’s index value was found to be 1.78 which revealed its soft nature. These optical, dielectric, piezoelectric, ferroelectric, mechanical and non-linear optical properties of grown crystal establish the usefulness of this material for optoelectronics, non-volatile memory and piezoelectric devices applications.
A bright orange-red emanating Ca
9
Bi
1−
x
(VO
4
)
7
:
x
Sm
3+
(
x
= 0.05–0.5) nanophosphor crystalline series has been synthesized for the first time through solution combustion route. X-ray ...diffraction pattern of Ca
9
Bi
0.80
Sm
0.20
(VO
4
)
7
was analyzed and processed using Rietveld Refinement. The nanophosphors synthesized were found to crystallize in trigonal crystal lattice with
R3c
(161) space group. The morphological behavior of prepared nanophosphors was studied by means of transmission electron microscopy (TEM). The photoluminescence nature of the nanophosphors corresponds to bright orange emission due to near-ultraviolet (NUV) excitation at 405 nm followed by
4
G
5/2
→
6
H
7/2
radiative relaxation. The chromaticity coordinates (
x
= 0.5504,
y
= 0.4484) are in harmony with the intense orange-red emission. The decay curves been well fitted in 1st-order exponential decay function indicate that a single type of crystallographic site is occupied by the dopant-Sm
3+
ions in host lattice. Auzel’s model was implemented to investigate into rates of nonradiative relaxation (302.008 s
−1
), radiative lifetime (0.76 ms), and quantum efficiency (81%) values. The crystalline and optical behavior of the synthesized orange-red emitting nanophosphors promote their usage in near UV-based WLEDS.
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