Inorganic materials with short radiative decay time are highly desirable for fast optical sensors. This paper reports fast photoluminescence (PL) from a series of barium hexafluorosilicate (BaSiF 6 ) superlong nanowires with high aspect ratios, codoped with Ce 3+ /Tb 3+ /Eu 3+ ions, with a subnanosecond decay time. Solvothermally synthesized BaSiF 6 nanowires exhibit a uniform morphology, with an average diameter less than 40 nm and aspect ratios of over several hundreds, grown in the c -axis direction with {110} surfaces. The PL emission from the codoped BaSiF 6 nanowires, when excited by a 254 nm source, is dependent on Tb 3+ concentration, and the energy transfer from Ce 3+ to Tb 3+ and to Eu 3+ ions allows efficient emissions in the visible spectra when excited by a near UV source. Annealing BaSiF 6 nanowires at 600 °C in a vacuum produced barium fluoride (BaF 2 ) nanowires composed of nanocrystals. Both BaSiF 6 and BaF 2 nanowires exhibit fast emissions in the visible spectra, with enhanced intensities compared with their codoped microparticle counterparts. The decay time of codoped BaSiF 6 nanowires is found to be shorter than that of codoped BaF 2 nanowires. The energy transfer is also observed in their cathodoluminescence spectra with high-energy irradiation.
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Luminescence characteristics of rare-earth-doped barium hexafluorogermanate BaGeF 6 nanowires: fast subnanosecond decay time and high sensitivity in H 2 O 2 detection
Fluorides are promising host materials for optical applications. This paper reports the photoluminescent (PL) and cathodoluminescent (CL) characteristics of barium hexafluorogermanate BaGeF 6 nanowires codoped with Ce 3+ , Tb 3+ and Sm 3+ rare earth ions, produced by a solvothermal route. The synthesized BaGeF 6 nanowires exhibit uniform morphology and size distribution. X-ray diffraction divulges the one-dimensional growth of crystalline BaGeF 6 structure, with the absence of any impurity phases. Visible luminescence is recorded from the nanowires in green and red regions, when the nanowires are codoped with Ce 3+ /Tb 3+ , and Ce 3+ /Tb 3+ /Sm 3+ , respectively, under a UV excitation source. The PL emission from the codoped BaGeF 6 nanowires, when excited by a 254 nm source, originates from the efficient energy transfer bridges between Ce 3+ , Tb 3+ and Sm 3+ ions. The decay time of the visible luminescent emission from the nanowires is in the order of subnanoseconds, being one of the shortest decay time records from inorganic scintillators. The CL emission from the BaGeF 6 nanowires in the tunable visible range reveals their potential use for the detection of high-energy radiation. The PL emissions are sensitive to H 2 O 2 at low concentrations, enabling their high-sensitivity detection of H 2 O 2 using BaGeF 6 nanowires. A comparison with BaSiF 6 nanowires is made in terms of decay time and its sensitivity towards H 2 O 2 .
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- Award ID(s):
- 1436120
- NSF-PAR ID:
- 10172648
- Date Published:
- Journal Name:
- RSC Advances
- Volume:
- 8
- Issue:
- 69
- ISSN:
- 2046-2069
- Page Range / eLocation ID:
- 39296 to 39306
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Compared to halides Cs2HfX6(X = Cl, Br, I) with a vacancy‐ordered cubic double perovskite structure, the halide Cs2HfF6(CHF), with a hexagonal Bravais lattice, possesses a higher mass density and chemical stability for radiation detection. Luminescence properties and energy transfer mechanisms of rare‐earths‐doped CHF materials are studied here. The structure of CHF is identified as a new type of vacancy‐ordered hexagonal perovskite, with the same type of building blocks of the double perovskite but stacked with single layers. Density‐functional theory calculations reveal a large bandgap of CHF. A broad emission is observed from the pristine CHF host, which is suggested to be associated with self‐trapped excitons (STEs). A series of rare‐earths‐doped materials are designed utilizing the STE emissions, and efficient energy transfers from STEs and Tb3+to Eu3+are achieved for tunable emissions. The codoped material shows stable emission under X‐ray irradiation, with 10.2% reduction from its initial emission intensity, associated with possible structural evolution by radiation‐induced deformation of the soft host. The radiation responses of singly and codoped materials are evaluated, and the codoped material is found to be more sensitive to the radiation energy than the singly doped or pristine CHF for radiation detection.
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Fabrication of highly stable, reversible, and efficient portable sensors for the detection of explosives for safety and security is challenging due to the robustness of the currently available detection tools, limiting their mass deployment to the explosion prone areas. This paper reports a new direction towards the sensing of nitro- and peroxide-based explosives using highly stable rare-earth-doped BaWO 4 nanofibers with remarkable sensitivity and reversibility. BaWO 4 nanofibers doped with Tb 3+ and Eu 3+ ions are fabricated through a sol–gel electrospinning process, and their emission characteristics and application as a fluorescent probe for the sensing of 2-nitrotoluene and H 2 O 2 , explosive taggants representing a broad class of explosives, are studied in detail. Scheelite structured BaWO 4 nanofibers exhibit excellent luminescence characteristics, and the rare-earth ion doping in the polycrystalline BaWO 4 nanofibers is tailored to achieve blue, green, red, and white light emissions. These nanofibers are extremely sensitive to 2-nitrotoluene and H 2 O 2 with rapid response time, and sensitivity is observed within the range of 1–400 ppb and 1–10 ppm, towards 2-nitrotoluene and H 2 O 2 , respectively. The fluorescence quenching of BaWO 4 nanofibers in the presence of 2-nitrotoluene and H 2 O 2 is exponential with the quenching constants up to 1.73 × 10 6 and 2.73 × 10 4 L mol −1 , respectively, which are significantly higher than those of most of the fluorescent probes based on metal–organic frameworks and conjugated organic materials. After exposing to 2-nitrotoluene, the luminescence of the nanofibers is retained completely upon heating at 120 °C for 10 min and the sensory response is retained as fresh nanofibers, and currently available fluorescent explosive sensors could not achieve such a recovery. The high sensitivity and selectivity of scalable rare-earth-doped BaWO 4 nanofibers provide a new platform for the simultaneous detection of two classes of explosives.more » « less
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/c8ra07806h
