Slow light and photon echoes in the F→D transition of Sm in single-crystal BaFCl.

Slow light effects induced by transient spectral hole-burning in the F→D transition of Sm in BaFCl at 688 nm are reported and a probe pulse delay of 1.25 μs was observed through a 5 mm thick crystal. This delay corresponds to a reduction of the group velocity v of the transmitted light to ∼4000 m/s.

Ultra-high-resolution greyscale fluorescence images UV-exposure of thin flexible phosphor films.

Thin films of BaFCl:Sm nanocrystals prepared using a polymer binder were used to create fluorescence images. The phosphor films were exposed to a UV-C mercury lamp light source chromium-coated quartz greyscale masks to create 4 μm resolution greyscale fluorescence images. The mechanism relies on the highly efficient conversion of Sm to Sm ions upon exposure to UV-C light which displays a large linear dynamic range.

Reversible Mn valence state switching in submicron α-AlO:Mn by soft X-rays and blue light - a potential pathway towards multilevel optical data storage.

The generation of Mn in α-AlO:Mn by soft X-ray exposure is demonstrated with a large dynamic range of the X-ray generated Mn luminescence signal, indicating the potential use of α-AlO:Mn for multilevel optical data storage. Samples with a range of Mn concentrations (0.05, 0.

Spin-forbidden near-infrared luminescence from a F colour centre generated upon annealing in mechanochemically prepared nanocrystalline BaLiF.

We report the properties of a unique colour centre in mechanochemically synthesized inverse perovskite BaLiF submicron crystals that are luminescent at ∼765 nm. The spin-forbidden luminescence with a lifetime of 5 ms is attributed to a F (F-centre aggregate) in the fluoride octahedra, with three fluoride anion vacancies (3F) filled with two electrons (2e). The Zeeman splitting of the electronic origin and its temperature dependence indicate that the transition is from a singlet excited state to a triplet ground state.

Ultra-slow electron spin-lattice relaxation in a low magnetic field enables massive optical spin polarization in theAground state of Crin ruby.

Ruby (α-AlOdoped with Cr) has been an archetypal material in the development of optical spectroscopy of the solid state for the last 150 years and was the first material that was demonstrated to lase. Notwithstanding the vast literature on ruby, one effect was somehow missed: in a magnetic field∼ 235 mT, the spin-lattice relaxation timefor the |+3/2⟩ level in theAground state is massively lengthened to ∼12 s at 1.4 K as demonstrated in this study.

Luminescence and photoionization of X-ray generated Sm in coprecipitated CaF nanocrystals.

We report photoluminescence and photoionization properties of Sm ions generated by X-irradiation of nanocrystalline CaF:Sm prepared by coprecipitation. The nanocrystals were of 46 nm average crystallite size with a distribution of ±20 nm and they were characterised by XRD, TEM and SEM-EDS. At room temperature, the X-irradiated sample displayed broad electric dipole allowed Sm 4f5d (A) → 4fF (T) luminescence at 725 nm that narrowed to an intense peak at 708 nm on cooling to ∼30 K.

On the origins of the green luminescence in the "zero-dimensional perovskite" CsPbBr: conclusive results from cathodoluminescence imaging.

There is great interest in the use of highly-efficient all-inorganic halide perovskites CsnPbBr2+n for optoelectronic applications. There however remains considerable debate as to the origins of the green luminescence in the zero-dimensional phase of the perovskite Cs4PbBr6, with theories suggesting it originates either from defects in the Cs4PbBr6 lattice or CsPbBr3 impurities/inclusions. The confusion has arisen due to the two phases being miscible and typically co-existing.

Towards rewritable multilevel optical data storage in single nanocrystals.

Novel approaches for digital data storage are imperative, as storage capacities are drastically being outpaced by the exponential growth in data generation. Optical data storage represents the most promising alternative to traditional magnetic and solid-state data storage. In this paper, a novel and energy efficient approach to optical data storage using rare-earth ion doped inorganic insulators is demonstrated.

Mechanochemically prepared SrFCl nanophosphor co-doped with Yb and Er for detecting ionizing radiation by upconversion luminescence.

We report a novel method for detecting ionizing radiation by employing the phenomenon of upconversion luminescence. Nanocrystalline SrFCl:Yb/Er was prepared by ball-milling and characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The photoluminescence properties of nanocrystalline SrFCl:Yb, SrFCl:Er and SrFCl:Yb/Er before and after X-irradiation were investigated.

Ultra-slow light propagation by self-induced transparency in ruby in the superhyperfine limit.

Self-induced transparency is reported for circularly polarized light in the R(-3/2) line of a 30 ppm ruby (α-AlO:Cr) at 1.7 K in a magnetic field of B‖c=4.5  T.

Controlled Generation of Tm Ions in Nanocrystalline BaFCl:Tm by X-ray Irradiation.

An investigation of the photoluminescence properties of divalent thulium generated by X-ray irradiation (X-irradiation) of nanocrystalline BaFCl:Tm (250 ± 50 ppm) is reported. The X-irradiated samples show typical Tm f-f luminescence with an excited state lifetime τ = 0.98 ± 0.

Photoreduction of Sm(3+) in Nanocrystalline BaFCl.

We demonstrate that exposure of nanocrystalline BaFCl:Sm(3+) X-ray storage phosphor to blue laser pulses with peak power densities on the order of 10 GW/cm(2) results in conversion of Sm(3+) to Sm(2+). This photoreduction is found to be strongly power-dependent with an initial fast rate, followed by a slower rate. The photoreduction appears to be orders of magnitude more efficient than that for previously reported systems, and it is estimated that up to 50% of the samarium ions can be photoreduced to the divalent state.

Room temperature hole-burning of X-ray induced Sm(2+) in nanocrystalline Ba0.5Sr0.5FCl0.5Br0.5:Sm(3+) prepared by mechanochemistry.

Alloyed nanocrystalline Ba0.5Sr0.5FCl0.

Mechanochemical preparation of nanocrystalline BaFCl doped with samarium in the 2+ oxidation state.

We report a facile mechanochemical preparation method for nanocrystalline BaFCl doped with samarium in the 2+ oxidation state by ball milling BaCl2, BaF2, and SmI2 under a nitrogen atmosphere. The resulting phosphors were characterized by powder X-ray diffraction; electron microscopy, X-ray photoelectron spectroscopy; and photoluminescence, photoexcitation, cathodoluminescence, and diffuse reflectance spectroscopy. This is the first report of a direct preparation method of Sm(2+) doped alkaline earth fluorohalides at room temperature and points to a significant potential for the preparation of a wide range of related X-ray storage phosphors containing rare earth ions in divalent and trivalent cationic states by mechanochemical methods.

Optical spectroscopy of graphene quantum dots: the case of C132.

We have reinvestigated the optical spectroscopy of C132 graphene quantum dots by absorption, selective fluorescence, excitation and time-resolved spectroscopy, the external heavy atom effect, and DFT based quantum chemical calculations. In particular, wavelength-selective photobleaching provides strong evidence for the assignment of the intrinsic absorption and emission features of the quantum dots and indicates that emissions observed at ∼670 and ∼630 nm and associated relatively narrow features that display vibrational progressions in the selective excitation spectra are due to different species. The emitting state that leads to a broad emission (1700 cm(-1)) centered around 750 nm appears to be a "near-dark" singlet state with a relatively long lifetime of ∼30 ns.

Controlling pulse delay by light and low magnetic fields: slow light in emerald induced by transient spectral hole-burning.

Slow light based on transient spectral hole-burning is reported for emerald, Be(3)Al(2)Si(6)O(18):Cr(3+). Experiments were conducted in π polarization on the R(1)(± 3/2) line (E2 ← A(2)4) at 2.2 K in zero field and low magnetic fields B||c.

Effects of postannealing on the photoluminescence properties of coprecipitated nanocrystalline BaFCl:Sm3+.

Nanocrystalline BaFCl:Sm(3+), as prepared by coprecipitation from aqueous solutions, is an efficient photoluminescent X-ray storage phosphor. In the present study, we report effects on its photoluminescence properties resulting from postannealing treatment in air in the temperature range between 100 to 900 °C. Interestingly, upon annealing at temperatures from 200 to 600 °C in air, a small fraction of the Sm(3+) ions in nanocrystalline BaFCl can be reduced to Sm(2+) ions.

Cathodoluminescence microanalysis of irradiated microcrystalline and nanocrystalline samarium doped BaFCl.

BaFCl:Sm3+ is an efficient photoluminescent storage phosphor for ionizing radiation. Cathodoluminescence (CL) microanalysis enables the Sm2+ and Sm3+ oxidation states of samarium doped BaFCl to be easily identified, provides information about electron-beam and X-ray induced modification of BaFCl:Sm, and enables the synthesis dependent spatial distribution of samarium dopants of <100 ppm concentration to be determined with sub-100 nm resolution at 295 K. CL spectroscopy of BaFCl:Sm particles reveals broad CL emissions at ≈ 360 and ≈500 nm associated with V k (Cl-) and oxygen-vacancy defects in the BaFCl host lattice and fine structure CL emissions associated with major 4GJ → 6HJ (Sm3+) and 5DJ → 7FJ (Sm2+) transitions.

Slowing light down by low magnetic fields: pulse delay by transient spectral hole-burning in ruby.

We report on the observation of slow light induced by transient spectral hole-burning in a solid, that is based on excited-state population storage. Experiments were conducted in the R1-line (2E←4A2 transition) of a 2.3 mm thick pink ruby (Al2O3:Cr(III) 130 ppm).

Photoinduced electron transfer and persistent spectral hole-burning in natural emerald.

Wavelength-selective excited-state lifetime measurements and absorption, luminescence, and hole-burning spectra of a natural African emerald crystal are reported. The (2)E excited-state lifetime displays an extreme wavelength dependence, varying from 190 to 37 μs within 1.8 nm of the R(1)-line.

Probing the R lines in tris(acetylacetonato) chromium(III) and tris(3-bromo-acetylacetonato) chromium(III) by luminescence and excitation line narrowing spectroscopy.

Site-selective and narrowed luminescence and excitation spectra in the region of the (2)E <-- (4)A 2 transitions are reported for single crystals of Al(acac) 3/Cr(III) and Al(3-Br-acac) 3/Cr(III) (where acac is acetylacetonate). The R 2 line is pronounced in the brominated system and displays a comparable oscillator strength as the R 1 line. The (2)E splitting is found to be 138 cm (-1), and the (4)A 2 ground-state splitting is 1.

Revisiting the crystal structure and thermal properties of NaMgAl(oxalate)3 x 9 H2O/Cr(III): an extraordinary spectral hole-burning material.

We have reinvestigated the crystal structure and thermal properties of NaMgAl(oxalate)(3) x 9 H(2)O. In the thermal gravimetric analysis the steps of dehydration and decomposition/oxidation yield a mass change that is commensurate with 9 water molecules of hydration. Dehydration steps occur at 127, 171, and 201 degrees C whereas the oxalate ligand decomposes in steps at 403 and 424 degrees C with a final oxidation step at 692 degrees C.

Efficient X-ray generation of Sm2+ in nanocrystalline BaFCl/Sm3+: a photoluminescent X-ray storage phosphor.

Efficient X-ray generation of relatively stable Sm2+ centers is observed in nanocrystalline Sm3+-activated BaFCl, as prepared by a one-step wet chemical reaction. The conversion efficiency is approximately 50,000 times higher than that in microcrystalline BaFCl/Sm3+ prepared at 900 degrees C. The Sm2+ centers, and hence the radiation dose, can be directly monitored by the narrow photoexcited 5DJ-7FJ f-f luminescence lines.

Side-hole to anti-hole conversion in time-resolved transient spectral hole-burning of emerald: ground state level versus excited state population storage in low magnetic fields.

Time-resolved transient spectral hole-burning experiments in zero field and in low magnetic fields B( parallelc) are reported for the chromium(III) R(1)-line, 2A((2)E)<-- 2A((4)A(2)) of Chatham lab created emerald, Be(3)Al(2)Si(6)O(18)ratio Cr(III)(0.0017% per weight), in the temperature range of 3 to 12 K. In low magnetic fields and temperatures >5 K conversion of side-holes to anti-holes is observed with progressing time.

Probing the lowest energy chlorophyll a states of photosystem II via selective spectroscopy: new insights on P680.

We present the wavelength dependence of homogeneous holewidths of persistent spectral holes burnt in O2-evolving Photosystem II core complexes isolated from spinach, in the temperature range 2.5-8 K. The data supports the assignment that those chlorophylls which undergo persistent spectral hole-burning are specific CP43 and CP47-trap states that transfer their excitation energy to the reaction center.