Active Rare Earth Ions Research Articles

Two-Dimensional β-NaLuF4 Hexagonal Microplates

A simple hydrothermal method has been developed to synthesize monodisperse β-NaLuF4 microplates in a large scale. The microcrystals have a perfect hexagonal shape with a diameter of about 5.2 µm and a thickness of 300 nm. Trisodium citrate (Cit3-), which is introduced into the reaction mixture and acts as the chelating agent and shape modifier, plays a key role in fine-tuning the microstructures. The dominant adsorption of Cit3- onto the {0001} facets lowers the surface energy of these facets. Consequently, the typical growth in the [0001] direction is prohibited, and the growth of nuclei is driven along the six symmetric directions ±[101̅0], ±[11̅00], and ±[011̅0], which directly results in the formation of β-NaLuF4 microplates. The microstructure and growth mechanism of β-NaLuF4 microplates are discussed in detail. Additionally, we investigated the photoluminescence properties of β-NaLuF4:Ln3+ (Ln = Eu, Tb, and Yb/Er). This powerfully demonstrates that β-NaLuF4 is an excellent host lattice for down-conversion and up-conversion luminescence of various optically active lanthanide ions.

Intramolecular energy transfer and luminescence enhancement effect in inert rare earth ions (La, Y, Gd)–Eu 3+ (Tb 3+) co-fabricated organic–inorganic hybrid materials by covalent grafting

In this paper, a novel kind of organic–inorganic monomer, HIPA-TESPIC, has been achieved by modifying 5-hydroxyisophthalic acid (abbreviated as HIPA) with 3-(triethoxysilyl)-propyl isocyanate (abbreviated as TESPIC). The organic–inorganic monomers (HIPA-TESPIC) with two components equipped with covalent bonds can behave as a functional molecular bridge, which can not only coordinate to RE ions but also occur in in situ sol–gel process with inorganic host precursor tetraethoxysilane (TEOS), resulting a kind of molecular hybrid material (named as RE-HIPA-TESPIC) with double chemical bond (RE–O coordination bond and Si–O covalent bond). 1H NMR, Fourier transform infrared (FT-IR) were applied to characterize the structure of HIPA-TESPIC and UV–vis spectrophotometer, phosphorescence, and luminescence spectra were applied to characterize the photophysical properties of the obtained hybrid material. Luminescent hybrid materials consisting of active rare earth ions (Tb 3+, Eu 3+)–inert rare earth ions (Y 3+, La 3+, Gd 3+) complex covalently bonded to a silica-based network have been obtained in situ via a sol–gel approach. Through co-hydrolysis and polycondensation, active rare earth ions and inert rare earth ions can be introduced in the same organic–inorganic hybrid monomer and then formed Si–O backbones. The luminescent behavior has been studied with the different ratios of active rare earth ions–inert rare earth ions, which suggests that the existence of inert rare earth ions can enhance the luminescence intensity, which may be due to the intramolecular energy transfer between inert rare earth ions and active rare earth ions.

Investigation of the TL response of [formula omitted]: [formula omitted] crystals to X and gamma radiation fields

Double potassium yttrium fluoride crystals doped with optically active rare earth ions have been recently shown to be attractive thermoluminescence (TL) materials for ionizing radiation dosimetry. In this context appropriate studies have been performed to test TL response of K 2 YF 5 crystals doped with Dy 3 + ions to photon radiation fields. Within the framework of this research K 2 YF 5 crystals doped with 0.2, 1.0, 2.0, 5.0 and 10.0 at% Dy 3 + as well as K 2 DyF 5 and undoped K 2 YF 5 crystals have been synthesized under hydrothermal conditions. Polished crystal platelets with thickness of about 1 mm have been irradiated with X and gamma rays in order to study TL sensitivity as well as dose and energy response properties of these compositions in terms of the Dy 3 + concentration. Within this concentration series, K 2 YF 5 crystals doped with 1.0 at% Dy 3 + have been found to have maximum TL response due to a main dosimetric TL peak, which can be deconvoluted in three TL glow peaks centered at 96.4, 104.9 and 130.7 ∘ C , with reasonable linearity behavior over the studied dose range and good reproducibility of dose measurements. The sensitivity increase is observed for previously gamma-sensitized samples and this sensitization process seems also to induce the appearing of the TL glow peak at 130.7 ∘ C . As it has been turned, the linear TL signal coefficient for K 2 Y 0.99 Dy 0.01 F 5 is comparable to that of a CaSO 4 :Mn TL dosemeter, irradiated with a 137Cs gamma radiation source at the same conditions. Photon energy dependence of TL response for K 2 Y 0.99 Dy 0.01 F 5 has been evaluated and it has been found that TL response of this composition to the 41.1 keV X-rays is 30 times higher than that to the 662 keV gamma rays. This fact points out that K 2 YF 5 crystals doped with Dy 3 + have potential as promising materials to be used for low-dose dosimetry in X-rays diagnostic or industrial radiography.

Rare earth ions and Ge nanocrystals inSiO2

Experimental studies of Ge nanocrystals embedded inSiO2 films doped with Er and Yb deposited by rf-magnetron sputtering are presented. Althoughinter-band photoluminescence (PL) from the Ge nanocrystals is not observed, it is neverthelessfound that the presence of Ge nanocrystals is crucial for obtaining light emission fromEr3+ andYb3+. Forboth kinds of rare earth ions, the intensity of the related PL line has a maximum after heat treatmentat 800 °C, and the PL excitation spectra for the two cases are very similar. This suggests that thepresence and the structure of the nanocrystals are important for the efficiency of PL fromEr3+ and Yb3+. Experiments performed with multilayer structures of Ge nanocrystals andSiO2 show that the optically active rare earth ions are located in theSiO2 layers, and not inside the Ge nanocrystals. The mechanism of energy transfer from Genanocrystals to the rare earth ions is found to be non-optical.

Synthesis, electrical properties, and optical characterization of Eu3+-doped La2Mo2O9 nanocrystalline phosphors

The lanthanum molybdate phosphor, La2Mo2O9, is a new fast ionic conductor that has shown potential uses as a nanocrystalline matrix for optically active lanthanide ions. Eu3+-doped La2Mo2O9 phosphors were prepared from freeze–dried powder precursor and the nano-polycrystalline powders obtained were characterized by XRD, DSC, TG/DTA, SEM, impedance spectroscopy, and optical spectroscopy. The substitution of La3+ by Eu3+ in La2−xEuxMo2O9 suppresses partially the phase transition observed in the undoped samples and increases both the density of sintered pellets and the ionic conductivity. Polycrystalline powder and sintered pellets of La2Mo2O9 phosphor exhibits optical transitions in the UV–visible region at low temperature, although there is a luminescence quenching process with temperature. At room temperature orange and red emissions are only observed when doping with Eu3+ ions. Moreover, a nanocrystal-size dependent energy transfer process from the matrix to the Eu3+ ions occurs.

Quantum confinement in rare-earth doped semiconductor systems

Rare-earth doped materials are widely deployed in optoelectronics and optical telecommunications technology, despite the difficulties associated with doping silicon with optically active rare-earth ions. Nanotechnology promises new classes of materials and devices that exploit the unique optical and electronic properties of low-dimensional structures; in particular, quantum confinement can modify the electronic structure of semiconductor hosts in such a way as to greatly increase the radiative efficiency of the rare-earth dopant. This article reviews some of the recent developments in the field and highlights possible future directions.

Electron Spin Resonance Study of Yttrium Aluminum Garnet Films Doped with Nd and Yb Ions

Yttrium aluminum garnet (YAG) thin films doped with optical active rare earth ions grown on YAG substrate can be used as wave-guide laser. Measured layers YAG:Yb, Nd (grown by the isothermal liquid phase epitaxy (LPE)) was additionally doped with Ga and Lu ions in order to increase film refractive index and decrease strains in layers, respectively. Electron spin resonance measurements have been performed on a number of YAG:Yb, Nd thin films with Yb concentrations ranging from 0at.% to 15at.% and Nd concentration equals to 1 at.% and 3 at.%. It was found that the measured angular dependence of the Yb3☎ ion linewidth is typical for a mosaic structure. Moreover, it was shown that internal strains in the layers depend on the kind of dopant as well as on their concentration.

FLUORIDE PHOSPHATE AND PHOSPHATE GLASSES FOR PHOTONICS

Phosphate (P) and fluoride phosphate (FP) glasses are attractive materials for a wide range of photonic applications such as lasers, amplifiers, photosensitivity, optical storage and Faraday rotators. They demonstrate high W transmission, low linear and nonlinear refractive index, low viscosity and low melting temperatures, athermal behaviour. In addition, they are excellent host materials for active rare earth (RE) ions due to advantageous local structure effect and high RE ion solubility. The paper reviews the benefit of FP and P glass properties for different photonic applications. Base glass properties, local structure and its effect on RE ion properties are described for FP and P glasses studied by the author. The potential of the glasses for laser, amplifier and photosensitivity-based devices are demonstrated.

Dopant distribution and energy transfer processes in crystals

This paper discusses the effects of the mutual asymmetric crystal field perturbations produced by near active and sensitizer ions in co-doped crystals. It is shown that modification of the spectral and dynamic properties of the perturbed ions justifies the division of the active and sensitizer ions systems in homogeneous subsystems and the particularities of energy transfer processes in these subsystems are presented. The discussion is illustrated for active rare earth ions in garnet crystals sensitized by Cr 3+ (in octahedral sites), Fe 3+ (in tetrahedral sites) or Yb 3+ (in dodecahedral sites). It is thus shown that the emission in sensitized laser crystals manifests different spectral and temporal properties from crystals with simple activation.

The luminescence and structure of novel transparent oxyfluoride glass-ceramics

New transparent oxyfluoride glass-ceramics can provide a low phonon energy fluoride environment for active rare earth ions while maintaining the formability and physical properties of an oxide glass. Transparent glass-ceramics were made by casting crucible melted glass onto a steel plate and subsequently heating the resultant glass patty above the glass transition temperature to nucleate and grow LaF 3 crystals. Eu 3+ doped glasses emit only red luminescence from the 5D 0 level but after heat treatment emit blue, green, and red luminescence indicative of a low phonon energy rare earth environment. TEM micrographs and XRD show no features in the base glass, but do show extensive LaF 3 crystallites after heat treatment that are responsible for the novel optical properties of these hybrid materials.

Synthesis and Luminescence of Lanthanide Ions in Nanoscale Insulating Hosts

This review summarizes recent work in nanostructured insulating materials that contain optically active lanthanide ions. These materials find applications in lasers, optical amplifiers, and optical-display phosphors. This review concentrates on the synthesis and luminescence spectroscopy of lanthanide-containing nanostructured particles, films, and composites. Spectroscopic studies range from basic luminescence spectroscopy and quantum efficiency measurements to high-resolution spectroscopic studies that investigate the phonon dynamics and electron−phonon interaction as a function of particle size. This review identifies several areas for further study, including the location, distribution, or segregation of dopants in nanoparticles; the efficiency of energy transfer across interfaces; and the effects of quantum confinement or changes in phonon dynamics and electron−phonon interactions on the radiative and nonradiative relaxation rates in localized luminescent dopants.

Towards composite solid state laser materials

The largest recent advance in the field of solid state materials is the exponential development of the Erbium doped fibre amplifiers, the so-called EDFAs, which are already implemented in many telecommunication systems. One is already interested in the evolution of such amplifiers towards more compact devices which could be obtained through Erbium doped wave guide amplifiers. The conditions for wave guide amplifiers are first discussed showing that it will be difficult to limit the active length to less than a few tenths of a centimetre in usual glasses without having to increase the active ion concentration up to the point where self-quenching reduces prohibitively the quantum efficiency of the amplifying transition. This leads us to consider new glassy materials where the inhomogeneous linewidth of the active ions shall be reduced in order to correlatively increase the gain cross-sections. An historical review of such an approach will be presented. Then we show that composite materials of the vitroceramic type where the active rare earth ion stays only in the microcrystalline phase, provide materials with reduced inhomogeneous broadening and with crystal type optical spectra though obtained by glass technics. Evaluations of the gain cross-sections indicate increases of at least 100%. Such composite materials may so pave the way for wave guide amplifiers.

Power-gated spectral holeburning in MgS:Eu2+, Eu3+: A case for high-density persistent spectral holeburning

We present the case of photoionization-induced holeburning in rare-earth-doped II–VI compounds for high-density persistent holeburning. In this case, the photoproduct of holeburning is distributed across the entire zero-phonon line. This maximizes the total number of possible spectral holes that can be burned into an inhomogeneous line as well as produces holes that are photoerasable. Experimental data on photon-gated holeburning in MgS:Eu2+, Eu3+ are presented. With the proper choice of the host electronic band structure, the optically active rare-earth ion and its electronic transitions involved in the holeburning process, to the best of our knowledge we have observed the highest number of photon-gated holes ever burned in a single electronic transition. The features of these holes are that they suffer no detectable erasure after several thousands of read cycles, they survive thermal cycling to ∼150 K, and they are completely photoerasable. A special case of photon-gated holeburning, power-gated holeburning, was employed to demonstrate that, in such systems, a single laser can be used for burning, reading, and erasing of the spectral holes.

RBS/channeling to locate active ions in laser materials: application to rare earth activated LiNbO 3

The potentiality of Rutherford backscattering spectrometry, used in channeling mode, to locate ions in laser crystals is tested by studying the case of trivalent rare earth active ions in LiNbO 3 crystals. It is shown that these active ions occupy Li + sites but off-centered from the regular lithium position by different amounts. These displacement are directly related to the ionic radii of the active ions. First evidence of multicenter structure obtained by RBS/channeling is reported for Pr 3+ ions in LiNbO 3. Taking advantages of this multicenter structure the crystal field parameter can be experimentally obtained for each center. Thus, it is shown how small variations of crystal field parameters, as a consequence of the non-equivalent centers, account for features observed in the optical spectra of Nd 3+ ions in this crystals.

Diode pumped holmium, thulium and erbium lasers between 2 and 3 micrometers operating cw at room temperature

Diode-pumped cw lasers operating between 2 and 3 m in the heavy rare-earth activator ions are reviewed. In Ho,Tm:YAG we demonstrated high efficiency using Tm as the sensitizer ion, which absorbed the pump radiation. This is followed by a cross-relaxation process, which allows two excited Tm ions to be produced from one absorbed photon. There is rapid energy migration among the Tm ions, followed by energy transfer to the Ho ion. The 2 pm laser action is to a level 460 cm1 above the ground state. In Tm,Ho:YLF we demonstrated cw cascade laser emission at 2.31 and 2.08 rim. Above threshold for both transitions, two infrared photons are produced for each absorbed pump photon. The theoretical slope efficiency ofthis system is 72.3% for pumping at 0.791 pm. In Er:YLF, cw laser emission at 2.8 im with a 10% slope efficiencywas demonstrated. The laser transition is normally self-terminating, but an upconversion process, which depopulates the lower laser level and populates the upper laser level, allows this transition to operate in a cw mode.

Incorporation of increased concentrations of rare earth activator ions in optical quality single crystals of yttrium aluminum garnet

There is a substantial mismatch in the ionic radius of the Nd 3+ ion and the Y 3+ ion, which, in part, is the reason for the difficulty encountered in the isomorphous substitution of large concentrations of the former ion in optical quality single crystals of yttrium aluminum garnet. In addition, attempts to prepare a garnet structural type compound of composition Nd 3Al 5O 12 have not been successful. Methods for increasing the concentration of Nd 3+ ions in optical quality single crystals of yttrium aluminum garnet by the simultaneous incorporation of size compensating cations were investigated. Crystal growth experiments have been carried out utilizing gallium, lutetium and ytterbium ions as the size compensating agent. Flourescence, lifetime and absorption measurements have been made to determine the effect of lutetium upon the optical properties of neodymium doped yttrium aluminum garnet.

Thermoluminescence method for the study of highly excited states of rare earth activator ions in crystals

Thermoluminescence method for the study of highly excited states of rare earth activator ions in crystals