Optical Properties Of Rare Earth Ions Research Articles

Rare earth-implanted lithium niobate: Properties and on-chip integration

We investigated the optical properties of rare-earth ions (Yb3+ and Er3+) implanted into lithium niobate (LN) crystals and observed superluminescent emission from a sheet of Yb ions in the Yb-implanted LN crystal (Yb:LN). Moreover, by directly integrating the Er-implanted LN crystal (Er:LN) with a silicon photonic chip with waveguide and resonator structures, we observed the evanescent coupling of photoluminescent light from the Er ions to the optical modes of the waveguide and microcavity. We measured an optical quality factor of about 104 and observed a modification of the photoluminescent emission from Er3+ ions in the integrated structure. The platform can ultimately enable developing the integrated multifunctional quantum photonic devices.

Effect of solvents on the morphology and optical properties of rare-earth ions doped BiOBr 3D flower-like microparticles via solvothermal method

Eu3+ or Sm3+ ions individually doped bismuth oxybromide (BiOBr) phosphors with three-dimensional flower-like microsphere morphology were prepared by a solvothermal method. The variation of ethylene glycol and ethanol concentrations affected the surface morphology of microparticles, which was investigated by field-emission scanning electron microscope images. The crystallinity and phase formation of BiOBr microspheres were analyzed by X-ray diffraction patterns, confirming the tetragonal phase with space group of P4/nmm (129). The photoluminescence (PL) properties were measured for the Eu3+or Sm3+ ions single doped BiOBr phosphors. From the temperature-dependent PL emission spectra, the activation energies of the Eu3+or Sm3+ ions single doped BiOBr samples were estimated. The PL emission spectra of the BiOBr:Eu3+ phosphors exhibited a reddish orange emission at 616 nm due to the characteristic 5D0 → 7F2 electronic transition at a blue excitation wavelength of 464 nm. The Sm3+ ions doped BiOBr phosphors revealed an emission at 603 nm of wavelength under the excitation wavelength of 408 nm. Also, the PL emission intensities of the optimized BiOBr:Eu3+ and BiOBr:Sm3+ samples were increased after calcination at 500 °C.

Nanostructured hybrid films containing nanophosphor: Fabrication and electronic spectral properties

The intensive research of the optical properties of rare-earth ions is due to the high quantum efficiency of their emission, very narrow bands, and excellent fluorescence monochromaticity. The photoluminescence data presented here show that the nanophosphor remains a green emitter in Layer-by-Layer (LbL) films leading to potential application in optical devices or biological labeling. The LbL technique, an established method for thin film fabrication with molecular architecture control, is used in the manufacture of a hybrid film containing the cationic polyelectrolyte poly (allylamine hydrochloride) (PAH) and Y2O3: Er, Yb nanophosphor. The spectroscopic properties of this luminescent nanomaterial are extracted from the spectral data of the powder, cast film and LbL films. The growth of the LbL film was monitored by absorbance versus concentration plots in ultraviolet–visible (UV–Vis) absorption spectroscopy. The presence of both PAH and nanophosphor in the LbL film was confirmed by Fourier transform infrared (FTIR) absorption spectroscopy. The FTIR data also ruled out the existence of chemical interactions between the PAH and nanophosphor layers, which means that secondary interactions (like Van der Waals forces) might be the driving forces for LbL film growth. The morphology and the spatial distribution of the LbL film components along the film surface were probed with micrometer spatial resolution combining optical microscopy and Raman mapping. In addition, the observation of intense electronic emission lines from doping ions showed micro-spectroscopy as a highly sensitive analytical technique for characterization of films containing nanophosphors.

Er3+‐Doped Anatase TiO2 Nanocrystals: Crystal‐Field Levels, Excited‐State Dynamics, Upconversion, and Defect Luminescence

A comprehensive survey of electronic structure and optical properties of rare-earth ions embedded in semiconductor nanocrystals (NCs) is of vital importance for their potential applications in areas as diverse as luminescent bioprobes, lighting, and displays. Er3+ -doped anatase TiO2 NCs, synthesized via a facile sol-gel solvothermal method, exhibit intense and well-resolved intra-4f emissions of Er3+ . Crystal-field (CF) spectra of Er3+ in TiO2 NCs are systematically studied by means of high-resolution emission and excitation spectra at 10-300 K. The CF analysis of Er3+ assuming a site symmetry of C(2v) yields a small root-mean-square deviation of 25.1 cm(-1) and reveals the relatively large CF strength (549 cm(-1) ) of Er3+, thus verifying the rationality of the C(2v) symmetry assignment of Er3+ in anatase TiO2 NCs. Based on a simplified thermalization model for the temperature-dependent photoluminescence (PL) dynamics from (4) S(3/2) , the intrinsic radiative luminescence lifetimes of (4) S(3/2) and (2) H(11/2) are experimentally determined to be 3.70 and 1.73 μs, respectively. Green and red upconversion (UC) luminescence of Er3+ can be achieved upon laser excitation at 974.5 nm. The UC intensity of Er3+ in Yb/Er-codoped NCs is found to be about five times higher than that of Er-singly-doped counterparts as a result of efficient Yb3+ sensitization and energy transfer upconversion (ETU) evidenced by its distinct UC luminescence dynamics. Furthermore, the origin of defect luminescence is revealed based on the temperature-dependent PL spectra upon excitation above the TiO2 bandgap at 325 nm.

Spectroscopic properties of Tm3+ ions in chalcogenide Ge–As–S glass containing minute amount of Ga and CsBr

We have experimentally confirmed that the absorption and emission properties for intra-4f-configurational transitions of Tm3+ ions doped in Ge–As–S glass, one of representative chalcogenide glasses, are modified dramatically upon the introduction of minute amount of Ga and CsBr, tantamount to a low doping level. This compositional adjustment makes local chemical environments of Tm3+ being rearranged spontaneously without any further thermal treatment applied. The hypersensitive 3H6↔3F4 transition, in particular, turns out to reflect the modified chemical environments more significantly than other transitions. Redistribution of the stark levels of 3F4 manifold is mainly responsible for the significant changes in emission spectra for 3H4→3F4 and 3F4→3H6 transitions. Since the addition of small amount of the group III elements and alkali halides alters only the optical properties of rare-earth ions, while keeping thermal stability of the chalcogenide glass hosts unchanged, our compositional adjustment method would be quite useful for practical applications of rare-earth activated chalcogenide glasses.

Recent Progress on the Spectroscopy of Rare Earth Ions in Core–Shells, Nanowires, Nanotubes, and Other Novel Nanostructures

Research and development of nanoscale luminescent and laser materials are part of the rapidly advancing nanoscience and nanotechnology. Because of unique spectroscopic properties and luminescent dynamics of f-electron states, doping luminescent rare earth ions into nano-hosts has been demonstrated as an optimistic approach to developing highly efficient and stable nanophosphors for various applications. In this article, we review the most recent progress in spectroscopic measurements of rare earth ion-activated low-dimensional nanostructures including nanolayers, core-shells, nanowires, nanotubes, and nanodisks. Among a large volume of work reported in the literature on many members of the rare earth series including Ce3+, Pr3+, Nd3+, Eu3+, and Er3+, we focus on recent findings in the spectroscopic and luminescence properties of Eu3+ doped nanolayers, core-shells, and nanotubes, because Eu3+ ions have been extensively studied and widely used as an ideal probe for fundamental understanding of nano-phenomena. Specifically, the dependence of the optical properties of rare earth ions on nanostructures is discussed in detail.

Nonoxide Glass-Forming Systems-Glass Formation and Structure, and Optical Properties of Rare-Earth Ions in Glasses

Nonoxide glasses composed of halides and/or chalcogenides (sulfides, selenides, and tellurides) as their main components have been extensively investigated due to their characteristic structures and properties. Among them, the present review focuses on glass formation based on nonfluoride-halide (halides other than fluoride) systems and the structure of the glasses as well as the transition properties of rare-earth ions in the nonoxide glasses. Systematic examination of glass formation in nonfluoride-halide systems based on AXn-MX-M′X2 with a single halide ion revealed that the systems of A=Zn, Cd, Ag, Cu and Li are vitrified by a conventional melting-cooling method, where X=Cl, Br, or I, M=alkali metal (K, Rb, Cs), and M′=alkaline earth metal (Ba). The coordination structure around the cations, An+, was investigated by means of X-ray absorption spectroscopy and other methods. The structural model for these halide glasses is also discussed. The studies about the transition properties of rare-earth ions in the nonoxide glasses showed that the multiphonon relaxation rates are strongly suppressed. Detailed analyses on the fluorescent decay curves for Er3+-doped Ga2S3-based glasses are presented.

Site-selective fluorescence spectroscopy of Eu 3+ and Sm 2+ ions in glass

Fluorescence line–narrowing or site-selective fluorescence experiments on Eu 3+ and Sm 2+ ions in glass are reviewed. It is shown that this technique gives detailed information that is difficult to obtain by other means, such as site-dependent homogeneous widths, inhomogeneous broadening mechanisms, distribution of crystal-field components in glass, and so on. A simple theoretical treatment to consider only the second-order terms of the crystal-field potential is discussed and is shown to be very effective. It will be emphasized that J-mixing, i.e., wave function mixing between 4f N states through the static crystal-field potential, plays a significant role in the optical properties of rare-earth ions in glass.

Photostimulated luminescence from CaS:Eu,Sm clusters embedded in organic dye

The optical properties of rare-earth ions in an organic dye matrix have been studied because of their possible application for optical information storage. Strong IR photostimulated luminescence of CaS:Eu,Sm doped organic dye films was revealed in the sample prepared by the sol–gel method. It was found that the efficiencies of photostimulated luminescence in the CaS:Eu,Sm doped pyrazoline dye films are higher than that in the inorganic CaS:Eu,Sm materials. The grain size of the nanocrystallites, determined by X-ray diffraction, is approximately 50 nm. It was shown that the absorption spectra for organic dye films exhibit a remarkable anisotropy near a wavelength of 310 nm.

Optical Properties of Rare‐Earth Ions in Lead Germanate Glasses

Glasses of composition (x ‐ 1)PbO(100 ‐ x)GeO21Ln2O3, with x= 30 mol% (Ln = Nd, Eu, Er), 40 mol% (Ln = Pr, Nd, Sm, Eu, Dy, Ho, Er, Tm), and 50 mol% (Ln = Eu, Er), have been prepared by quenching the oxidic melts. From the optical absorption and emission spectra in the ultraviolet‐visible‐near‐infrared (UV‐VIS‐NIR) region, the intensity parameters, spontaneous emission probabilities, branching ratios, radiative lifetimes, and, for selected NIR transitions, peak stimulated emission cross sections have been obtained. The trends observed in the intensity parameters have been discussed, as a function of the number of f electrons as well as a function of the lead content. As the amount of lead increases, the covalency of the Ln‐O bond increases, the symmetry of the rare‐earth site increases, and the dopant site distribution narrows. The peak stimulated emission cross sections rank among the highest found for oxide glasses.

Excitation mechanisms and optical properties of rare-earth ions in semiconductors.

The optical activity of rare-earth ions in semiconductors is discussed taking into account the large 4f-level correlation energy. In addition to crystal-field effects, three many-body excitation mechanisms of 4f-4f transitions are identified; coherent or incoherent energy transfer via electron-hole pairs and nonequilibrium electron excitation. The first two give rise to novel nonlinear optical effects, while the last promises a simple means of achieving optical gain.