Recent startling interest for lanthanide luminescence is stimulated by the continuously expanding need for luminescent materials meeting the stringent requirements of telecommunication, lighting, electroluminescent devices, (bio-)analytical sensors and bio-imaging set-ups. This critical review describes the latest developments in (i) the sensitization of near-infrared luminescence, (ii) “soft” luminescent materials (liquid crystals, ionic liquids, ionogels), (iii) electroluminescent materials for organic light emitting diodes, with emphasis on white light generation, and (iv) applications in luminescent bio-sensing and bio-imaging based on time-resolved detection and multiphoton excitation (500 references).

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Lanthanide luminescence for functional materials and bio-sciences

Control of spontaneously emitted light lies at the heart of quantum optics. It is essential for diverse applications ranging from miniature lasers and light-emitting diodes, to single-photon sources for quantum information, and to solar energy harvesting. To explore such new quantum optics applications, a suitably tailored dielectric environment is required in which the vacuum fluctuations that control spontaneous emission can be manipulated. Photonic crystals provide such an environment: they strongly modify the vacuum fluctuations, causing the decay of emitted light to be accelerated or slowed down, to reveal unusual statistics, or to be completely inhibited in the ideal case of a photonic bandgap. Here we study spontaneous emission from semiconductor quantum dots embedded in inverse opal photonic crystals. We show that the spectral distribution and time-dependent decay of light emitted from excitons confined in the quantum dots are controlled by the host photonic crystal. Modified emission is observed over large frequency bandwidths of 10%, orders of magnitude larger than reported for resonant optical microcavities. Both inhibited and enhanced decay rates are observed depending on the optical emission frequency, and they are controlled by the crystals’ lattice parameter. Our experimental results provide a basis for all-solid-state dynamic control
of optical quantum systems.

Controlling the dynamics of spontaneous emission from quantum dots by photonic crystals

A review of some properties of chalcogenide glasses and the current status of their applications is given. Techniques to characterize the linear and non-linear properties of these glasses are introduced and used to measure the optical constants of chalcogenide glasses in the form of bulk, thin film and fiber. Different techniques for the fabrication of gratings and waveguides in these glasses are described. Achievable efficiencies of gratings, as well as propagation losses of fabricated waveguides, are presented. The possibilities of fabricating active devices, such as fiber amplifiers and lasers, are presented. Finally, a novel application of chalcogenide glasses, namely all-optical switching for the fabrication of efficient femtosecond switches, is introduced.

Optical properties and applications of chalcogenide glasses: a review

The chemistry of post transition metals is dominated by the group oxidation state N and a lower N-2 oxidation state, which is associated with occupation of a metal s2 lone pair, as found in compounds of Tl(I), Pb(II) and Bi(III). The preference of these cations for non-centrosymmetric coordination environments has previously been rationalised in terms of direct hybridisation of metal s and p valence orbitals, thus lowering the internal electronic energy of the N-2 ion. This explanation in terms of an on-site second-order Jahn–Teller effect remains the contemporary textbook explanation. In this tutorial review, we review recent progress in this area, based on quantum chemical calculations and X-ray spectroscopic measurements. This recent work has led to a revised model, which highlights the important role of covalent interaction with oxygen in mediating lone pair formation for metal oxides. The role of the anion p atomic orbital in chemical bonding is key to explaining why chalcogenides display a weaker preference for structural distortions in comparison to oxides and halides. The underlying chemical interactions are responsible for the unique physicochemical properties of oxides containing lone pairs and, in particular, to their application as photocatalysts (BiVO4), ferroelectrics (PbTiO3), multi-ferroics (BiFeO3) and p-type semiconductors (SnO). The exploration of lone pair systems remains a viable a venue for the design of functional multi-component oxide compounds.

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Stereochemistry of post-transition metal oxides: revision of the classical lone pair model.

Advances in solid state white lighting technologies witness the explosive development of phosphor materials (down-conversion luminescent materials). A large amount of evidence has demonstrated the revolutionary role of the emerging nitride phosphors in producing superior white light-emitting diodes for lighting and display applications. The structural and compositional versatility together with the unique local coordination environments enable nitride materials to have compelling luminescent properties such as abundant emission colors, controllable photoluminescence spectra, high conversion efficiency, and small thermal quenching/degradation. Here, we summarize the state-of-art progress on this novel family of luminescent materials and discuss the topics of materials discovery, crystal chemistry, structure-related luminescence, temperature-dependent luminescence, and spectral tailoring. We also overview different types of nitride phosphors and their applications in solid state lighting, including general ...

Down-Conversion Nitride Materials for Solid State Lighting: Recent Advances and Perspectives.

Vitrification of fly ash from municipal solid waste incinerator.

The infrared reflectance spectra at near-normal and off-normal incidence and polarized Raman spectra have been investigated to characterize the structure of PbOBi2O3Ga2O3 glasses. Infrared reflectance bands at 400 cm−1, 470 cm−1 and 610 cm−1 have been assigned to PbO, BiO and GaO related vibrations, respectively. The polarized Raman spectra were deconvoluted into seven bands which have been classified into four sets of modes: (1) depolarized low-frequency Raman modes at 30–70 cm−1, (2) strongly polarized Pb and Bi heavy metal vibrations at 120 to 140 cm−1: (3) polarized GaOPb, GaOBi, BiOPb, GaOGa and BiOBi bridging-oxygen modes at 300–600 cm−1; (4) non-bridging-oxygen modes at 600–700 cm−1. The optic vibrations observed in the series of glasses indicate that most cations behave essentially as network-formers. The low-frequency Raman scattering was analyzed on the basis of Martin and Brenig's acoustic model, from which some intermediate range structural information is derived. The structural correlation and structural units which determine the high frequency modes in these glasses are discussed.

Vibrational spectra and structure of heavy metal oxide glasses

Phosphor-in-glass (PiG) typed robust color converters were fabricated using Pb-free silicate glasses for high-power white LED applications. SiO2–B2O3–RO(R=Ba,Zn) glass powder showed good sintering behavior and high visible transparency under the sintering condition of 750 °C for 30 min without noticeable interaction with phosphors. By simply changing the thickness of the PiG plate or mixing ratio of glass to Y3Al5O12:Ce3+ phosphor, CIE chromaticity coordinates of the LED can be easily controlled. Enhanced thermal quenching property of PiG compared to phosphor with conventional silicone resin suggests its prominent feasibility for high-power/high-brightness white LEDs.

Phosphor in glasses with Pb-free silicate glass powders as robust color-converting materials for white LED applications

In comparison to other chalcogenide glasses, Ge–Ga–S glasses have the largest rare-earth solubility. Raman spectra of GeS2–Ga2S3 glasses contain two bands at 265 and 385 cm−1 which increased in intensity with the addition of Ga2S3. These are associated with the vibration of Ge–Ge bonds and edge-shared GaS4 tetrahedra, respectively. Upon the addition of La2S3 into GeS2–Ga2S3 glasses, intensities of these two bands decreased while a new band appeared at 375 cm−1 due to the vibration of tetrahedra with non-bridging sulfur(s). Dissociation of Ge–Ge bonds and edge-shared GaS4 tetrahedra through the addition of La2S3 are responsible for the non-bridging sulfur formation. La3+ can be dissolved into the glass network as charge compensators for these non-bridging sulfurs. Since no such structural unit is present in glasses without Ga2S3, this connection scheme and the structural modification in Ga-containing chalcogenide glasses seem to be crucial for an increase of La3+ solubility.

Raman spectroscopic analysis on the solubility mechanism of La3+ in GeS2–Ga2S3 glasses

The 1.3 μm fluorescent emissions from PbOBi 2 O 3 Ga 2 O 3 glasses doped with Pr 3+ or Dy 3+ were measured. Modified Judd—Ofelt analysis was applied to the Pr 3+ -doped glasses to obtain intensity parameters and radiative properties. Emission from the Pr 3+ : 1 G 4 → 3 H 5 transition in heavy metal oxide (HMO) glass was centered at the wavelength of 1320 nm with a spectral bandwidth of 100 nm. The lifetime of the 1 G 4 level was 53 μs with a quantum efficiency of 9%. Excited-state absorption near the 1.3 μm emission were comparable to those in fluoride glasses. Multiphonon relaxation rates in PbOBi 2 O 3 Ga 2 O 3 glasses calculated from the lifetimes were similar to those of fluoride glasses, but were the smallest among oxide glasses.

Jong Heo

Papers

Vitrification of fly ash from municipal solid waste incinerator.

Vibrational spectra and structure of heavy metal oxide glasses

Phosphor in glasses with Pb-free silicate glass powders as robust color-converting materials for white LED applications

Raman spectroscopic analysis on the solubility mechanism of La3+ in GeS2–Ga2S3 glasses

1.3 μm emission and multiphonon relaxation phenomena in PbOBi2O3Ga2O3 glasses doped with rare-earths