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).

/pdf/lanthanide-luminescence-for-functional-materials-and-bio-1w9cppwf8r.pdf

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.

/pdf/stereochemistry-of-post-transition-metal-oxides-revision-of-4y9tvku4se.pdf

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.

Electric-field assisted solid-state diffusion of Ag+ was used to control precipitation of PbS quantum dots (QDs) inside glasses. Precipitation of PbS QDs was confirmed by transmission electron microscopy images and photoluminescence (PL) spectra. PL bands moved to longer wavelengths as applied voltage increased under the same subsequent heat-treatment, and as heat-treatment temperature increased under the same voltage. PbS QDs can preferentially precipitate at low temperature and photo-luminesce at longer wavelengths in Ag+-affected regions than in unaffected regions. Ag nanoparticles were also formed inside affected regions after thermal treatment, and provided nucleation sites for PbS QDs. Precipitation of PbS QDs and their spatial distribution in glasses can be controlled by electric field-assisted Ag+ migration.

Electric field-assisted Ag+ migration for PbS quantum dot formation in glasses

Structure Analysis of Vitusite Glass–Ceramic Waste Forms Using Extended X-ray Absorption Fine Structures

PbS and PbS/CdS core/shell colloidal quantum dots (QDs) were mixed with As2S3 glass powders to prepare solid composite materials. PbS QDs showed an absorption band centered at a wavelength of λ = 1478 nm and a photoluminescence (PL) band centered at λ = 1547 nm. PbS/CdS core/shell QDs had higher PL intensity than did bare PbS QDs. Solid composites made by mixing QDs and As2S3 glass powders showed clear PL bands at λ = 1385 nm. Optical fibers of As2S3 glass can be prepared from these composite materials if appropriate scale-up technology is realized.

Photoluminescence from PbS quantum dots and PbS/CdS core/shell quantum dots mixed with As2S3 glass

Emission properties of PbO–Bi2O3–Ga2O3 glasses doped with Ho3+ were investigated for fiber-optic amplification at the 1.18 μm wavelength region. When the glasses were doped with Ho3+ ions only, there was a weak emission at 1.18 μm with a lifetime of ∼200 μs. However, when Yb3+ ions were codoped, the lifetime of the 1.18 μm emission increased to 630 μs together with a significant increase in intensity. A similar enhancement in the intensity and lifetimes was realized for the 2.05 μm emission. These effects are due to energy transfer from the Yb3+:2F5/2 to the Ho3+:5I6 level. Devitrification of the ternary PbO–Bi2O3–Ga2O3 glasses was efficiently suppressed by adding 10 mol% GeO2. Optimum Ho3+ concentration was ∼0.4 mol%, whereas Yb3+ ions can be added up to the solubility limit.

Populations and Emission Properties of the 5I6 and 5I7 Levels in Ho3+ Doped into PbO–Bi2O3–Ga2O3 Glasses

Photo-induced phenomena in binary (PbO–Ga2O3) and ternary (PbO–Bi2O3–Ga2O3) heavy metal oxide glasses were investigated. A red shift up to ∼0.05 eV in the absorption edge of 75PbO–25Ga2O3 glass (mol%) was observed by illuminating the subbandgap light for 30 min. This shift was completely erased by the heat treatment near the glass transition temperature. Refractive index of the glass at 600 nm also increased ∼0.011 by the illumination. It is believed that the presence of lone-pair electrons associated with Pb-polyhedra is essential to realize a reversible photo-induced effect in these oxide glasses.

Jong Heo

Papers

Electric field-assisted Ag+ migration for PbS quantum dot formation in glasses

Structure Analysis of Vitusite Glass–Ceramic Waste Forms Using Extended X-ray Absorption Fine Structures

Photoluminescence from PbS quantum dots and PbS/CdS core/shell quantum dots mixed with As2S3 glass

Populations and Emission Properties of the 5I6 and 5I7 Levels in Ho3+ Doped into PbO–Bi2O3–Ga2O3 Glasses

Photo-Induced Effect in Heavy Metal Oxide Glasses