Before the 1960s, all anti-Stokes emissions, which were known to exist, involved emission energies in excess of excitation energies by only a few kT. They were linked to thermal population of energy states above excitation states by such an energy amount. It was the well-known case of anti-Stokes emission for the so-called thermal bands or in the Raman effect for the well-known anti-Stokes sidebands. Thermoluminescence, where traps are emptied by excitation energies of the order of kT, also constituted a field of anti-Stokes emission of its own. Superexcitation, i.e., raising an already excited electron to an even higher level by excited-state absorption (ESA), was also known but with very weak emissions. These types of well-known anti-Stokes processes have been reviewed in classical textbooks on luminescence.1 All fluorescence light emitters usually follow the well-known principle of the Stokes law which simply states that excitation photons are at a higher energy than emitted ones or, in other words, that output photon energy is weaker than input photon energy. This, in a sense, is an indirect statement that efficiency cannot be larger than 1. This principle is

Upconversion and Anti-Stokes Processes with f and d Ions in Solids

Sasidharan Swarnalatha Lucky,†,§ Khee Chee Soo,‡ and Yong Zhang*,†,§,∥ †NUS Graduate School for Integrative Sciences & Engineering (NGS), National University of Singapore, Singapore, Singapore 117456 ‡Division of Medical Sciences, National Cancer Centre Singapore, Singapore, Singapore 169610 Department of Biomedical Engineering, Faculty of Engineering, National University of Singapore, Singapore, Singapore 117576 College of Chemistry and Life Sciences, Zhejiang Normal University, Zhejiang, P. R. China 321004

Nanoparticles in photodynamic therapy.

Phosphor-converted white light-emitting diodes (pc-WLEDs) are emerging as an indispensable solid-state light source for the next generation lighting industry and display systems due to their unique properties including but not limited to energy savings, environment-friendliness, small volume, and long persistence. Until now, major challenges in pc-WLEDs have been to achieve high luminous efficacy, high chromatic stability, brilliant color-rending properties, and price competitiveness against fluorescent lamps, which rely critically on the phosphor properties. A comprehensive understanding of the nature and limitations of phosphors and the factors dominating the general trends in pc-WLEDs is of fundamental importance for advancing technological applications. This report aims to provide the most recent advances in the synthesis and application of phosphors for pc-WLEDs with emphasis specifically on: (a) principles to tune the excitation and emission spectra of phosphors: prediction according to crystal field theory, and structural chemistry characteristics (e.g. covalence of chemical bonds, electronegativity, and polarization effects of element); (b) pc-WLEDs with phosphors excited by blue-LED chips: phosphor characteristics, structure, and activated ions (i.e. Ce 3+ and Eu 2+ ), including YAG:Ce, other garnets, non-garnets, sulfides, and (oxy)nitrides; (c) pc-WLEDs with phosphors excited by near ultraviolet LED chips: single-phased white-emitting phosphors (e.g. Eu 2+ –Mn 2+ activated phosphors), red-green-blue phosphors, energy transfer, and mechanisms involved; and (d) new clues for designing novel high-performance phosphors for pc-WLEDs based on available LED chips. Emphasis shall also be placed on the relationships among crystal structure, luminescence properties, and device performances. In addition, applications, challenges and future advances of pc-WLEDs will be discussed.

Phosphors in phosphor-converted white light-emitting diodes: Recent advances in materials, techniques and properties

Upconversion refers to non-linear optical processes that convert two or more low-energy pump photons to a higher-energy output photon. After being recognized in the mid-1960s, upconversion has attracted significant research interest for its applications in optical devices such as infrared quantum counter detectors and compact solid-state lasers. Over the past decade, upconversion has become more prominent in biological sciences as the preparation of high-quality lanthanide-doped nanoparticles has become increasingly routine. Owing to their small physical dimensions and biocompatibility, upconversion nanoparticles can be easily coupled to proteins or other biological macromolecular systems and used in a variety of assay formats ranging from bio-detection to cancer therapy. In addition, intense visible emission from these nanoparticles under near-infrared excitation, which is less harmful to biological samples and has greater sample penetration depths than conventional ultraviolet excitation, enhances their prospects as luminescent stains in bio-imaging. In this article, we review recent developments in optical biolabeling and bio-imaging involving upconversion nanoparticles, simultaneously bringing to the forefront the desirable characteristics, strengths and weaknesses of these luminescent nanomaterials.

Upconversion nanoparticles in biological labeling, imaging, and therapy

The 5d level positions of the trivalent lanthanides in inorganic compounds

Optical spectroscopy of electronic centers in solids.- Excitation transfer in disordered systems.- Dynamics of incoherent transfer.- General techniques and experimental methods in laser spectroscopy of solids.- High resolution laser spectroscopy of ions in crystals.- Laser excited fluorescence spectroscopy in glass.- Excitation Dynamics in Molecular Solids.- Addendum (to the Second Edition).

Laser spectroscopy of solids II

Mn2+ activated green, yellow, and red long persistent phosphors

Inorganic Phosphors: Compositions, Preparation and Optical Properties addresses practical and theoretical aspects of inorganic phosphors used in lighting and display applications. Authors Yen and Weber present the synthesis of phosphors in a ...cookbook... style that features nearly 300 ...recipes... using the most up-to-date guidelines and methods. They also categorize nearly 500 phosphors in terms of chemical composition and luminescence output wavelengths, summarizing their physical and emissive optical properties. This book is the first of its kind to provide a combined practical and technical foundation that can be used in commercial and academic research and development of new phosphors and applications.

Inorganic Phosphors: Compositions, Preparation and Optical Properties

Single-crystal CaAl2O4 fibers doped with Ce3+ or Tb3+ or double doped with Tb3+ and Ce3+ were prepared by the laser-heated pedestal-growth method. Ce3+-doped CaAl2O4 was found to have persistent phosphorescence in the blue violet lasting more than 10 h, while Tb3+-doped CaAl2O4 showed only a weak afterglow. However, long persistent green phosphorescence from Tb3+ was observed in the doubly doped fiber, CaAl2O4:Tb3+,Ce3+. It was found that the enhanced green phosphorescence from Tb3+ is due to persistence energy transfer from the thermally released electrons to Ce3+ followed by energy transfer to Tb3+. The finding suggests a promising approach for controlling the color of persistent phosphors.

Green phosphorescence of CaAl2O4:Tb3+,Ce3+ through persistence energy transfer

The disclosure provides long-persistent phosphors, methods for their manufacture and phosphorescent articles. The disclosure also provides a method for generating a longpersistent phosphorescence at a selected color. The phosphors of the disclosure may be alkaline earth aluminates, alkaline earth silicates, and alkaline earth aluminosilicates. The phosphors include those activated by cerium. The phosphors also include those in which persistent energy transfer occurs from a donor ion to an acceptor ion, producing persistent emission largely characteristic of the acceptor ion.

William M. Yen

Papers

Laser spectroscopy of solids II

Mn2+ activated green, yellow, and red long persistent phosphors

Inorganic Phosphors: Compositions, Preparation and Optical Properties

Green phosphorescence of CaAl2O4:Tb3+,Ce3+ through persistence energy transfer

Long persistent phosphors and persistent energy transfer techniques