Donor doping process and white light generation in CaMoO4 powders with multivalence Pr codoping

Both trivalent praseodymium (Pr³⁺) and quadrivalent praseodymium (Pr⁴⁺) were doped in molybdate powders. Visible emission from matrix was enhanced by multivalent Pr codoping. It was proposed that Pr³⁺ ions was donor and supplied quasi-free electron when Pr³⁺ took place the Pr⁴⁺ sites. The result showed that multivalence codoping would be an effective way to enhance emission of CaMoO₄. White light can be generated from Ca_0.98Pr_0.02MoO₄ powder via combination of broadband emissions originated from CaMoO₄ matrix and radiative transition of Pr³⁺. It showed warm white light with T_c of 3450 K that implies promising application in white light emitting diodes (LEDs).     

Rare-earth doped YF3 nanocrystals embedded in sol–gel silica glass matrix for white light generation

YF₃ nanocrystals triply-doped with Yb³⁺, Ho³⁺ and Tm³⁺ ions embedded in amorphous silica matrix have been successfully obtained by heat treatment of precursor sol–gel glasses for the first time to our knowledge and confirmed by X-ray diffraction and luminescence measurements. Simultaneous UV and visible efficient up-conversion emissions, with well-resolved Stark structure, under 980 nm infrared pump are observed, indicating the effective partition of rare-earth ions into a crystalline-like environment of the YF₃ nanocrystals. Corresponding energy transfer mechanisms have been analyzed and overall colour emission has been quantified in terms of standard chromaticity diagram. By an adequate doping level and heat treatment temperature of precursor sol–gel glasses, a bright white colour has been accomplished, close to the standard equal energy white light illumination point, with potential applications in photo-electronic devices and information processing.     

The luminescence properties of Er-doped and Er-Tm-co-doped phosphate glasses for white light emitting diode

Phosphate glasses and glass ceramics doped with Er³⁺ and co-doped with Er³⁺-Tm³⁺ are presented in this work. The luminescence properties have been characterized by absorption, excitation and emission spectra. All samples excited by blue light could emit a combination of blue/green/orange/red wavelength giving white light. For Er³⁺-doped glasses, a self-quenching effect has been obtained and an adjustable tune comes out after crystallization. For co-doped glasses, the red emission at 651 nm has been enhanced due to the existence of Tm³⁺, which could be relative to both the overlapped emissions and the energy transfer from Tm³⁺ to Er³⁺.     

A new concept of white light generation using a nano-waveguide for the solar radiation collection use

We propose a novel system of a nano-waveguide that can be used to generate the continuous optical spectrum, i.e. white light. A system consists of two micro-ring resonators and a nano-ring resonator that can be integrated into a single system. The large bandwidth signal is generated using a soliton pulse propagating within a Kerr-type nonlinear medium, whereas the continuous bandwidth or wavelength of light signal can be performed. Results obtained have shown the potential of using such a system for white light source generation and amplification, which is discussed. The amplified pulse can be stored within a nano-waveguide, which is allowed to form the continuous spectrum after amplification. Alternatively, the low-level solar radiation can be amplified, and the bandwidth signals can also be enlarged.     

Array illuminator based on self-imaging in white light

An array illuminator is a device/optical system that splits an incoming beam of light into an array of many light spots/beams. It is useful in logic systems and in optical digital computing or in switching systems to energize arrays of components such as logic gates, optically bistable devices and electro-optic modulators. Array illuminators working in white light are interesting because they do not suffer from coherent noise and yield better signal-to-noise ratio. We propose configurations for array illuminator based on Fresnel diffraction and working under white light illumination conditions. Performance evaluation of the illuminators is also undertaken and the results of investigation are reported.     

Enhanced white light emission in Er/Tm/Yb/Li codoped Y2O3 nanocrystals

Er/Tm/Yb codoped Y₂O₃ nanocrystals and Er/Tm/Yb/Li codoped Y₂O₃ nanocrystals have been synthesized by sol-gel method, bright white light emission has been observed at 976 nm excitation. The blue, green, and red emissions, respectively, arise from the transitions ¹G₄ → ³H₆ of Tm³⁺, ²H_11/2/⁴S_3/2 → ⁴I_15/2, and ⁴F_9/2 → ⁴I_15/2 of Er³⁺ ion. Moreover, after doping Li⁺ ions into Er/Tm/Yb codoped Y₂O₃ nanocrystals, the white light emission increase greatly. CIE coordinate of Er/Tm/Yb/Li codoped Y₂O₃ nanocrystals is X = 0.32 and Y = 0.36 at 10 W/cm² excitation, which is very close to the standard equal energy white light illuminate (X = 0.33, Y = 0.33).     

Eu/Tb ions co-doped white light luminescence Y2O3 phosphors

Y₂O₃:Eu³⁺, Tb³⁺ phosphors with white emission are prepared with different doping concentration of Eu³⁺ and Tb³⁺ ions and synthesizing temperatures from 750 to 950 °C by the co-precipitation method. The resulted phosphors were characterized by X-ray diffraction (XRD) and photoluminescence (PL) spectroscopy. The results of XRD indicate that the crystallinity of the synthesized samples increases with enhancing the firing temperature. The photoluminescence spectra indicate the Eu³⁺ and Tb³⁺ co-doped Y₂O₃ phosphors show five main emission peaks: three at 590, 611 and 629 nm originate from Eu³⁺ and two at 481 and 541 nm originate from Tb³⁺, under excitation of 250-320 nm irradition. The white light luminescence color could be changed by varying the excitation wavelength. Different concentrations of Eu³⁺ and Tb³⁺ ions were induced into the Y₂O₃ lattice and the energy transfer from Tb³⁺→Eu³⁺ ions in these phosphors was found. The Commission International de l’Eclairage (CIE) chromaticity shows that the Y₂O₃:Eu³⁺, Tb³⁺ phosphors can obtain an intense white emission.     

Structure and photophysical behavior of 2,2′-bipyrimidine/lanthanide ion complexes in various environments

The photophysical behavior of 2,2′-bipyrimidine has been studied alone and in the presence of several lanthanide or other metal ions. This substance, which is employed as bridging ligand in homo- and hetero-dinuclear complexes, can form stable complexes with luminescent lanthanide ions like Eu³⁺ and Tb³⁺. Complexes precipitated from common solvents are crystalline with a structure that consists of discrete, centrosymmetric dinuclear entities with a planar ligand configuration. These complexes are strongly luminescent. Luminescence is sensitized by ligand-to-metal energy transfer. However, when the ligand and metal ions are mixed in an unconventional solvent, like a poly(ethylene glycol) oligomer, all reagents stay in solution and produce a different type of complex where only an enhanced ligand-centered fluorescence can be observed. It is possible that such fluorescence is emitted by 2,2′-bipyrimidine in a non-planar configuration. This behavior has also been observed with other heterocyclic ligands that can exist in different conformers, like terpyridine, and it may explain why some ligand-lanthanide complexes sometimes fail to sensitize efficient photoluminescence.     

Evaluation of intramolecular energy transfer process in the lanthanide(III) bis- and tris-(TTA) complexes: Photoluminescent and triboluminescent behavior

This work reports the energy transfer mechanism process of [Eu(TTA)₂(NO₃)(TPPO)₂] (bis-TTA complex) and [Eu(TTA)₃(TPPO)₂] (tris-TTA complex) based on experimental and theoretical spectroscopic properties, where TTA=2-thienoyltrifluoroacetone and TPPO=triphenylphosphine oxide. These complexes were synthesized and characterized by elemental analyses, infrared spectroscopy and thermogravimetric analysis. The theoretical complexes geometry data by using Sparkle model for the calculation of lanthanide complexes (SMLC) is in agreement with the crystalline structure determined by single-crystal X-ray diffraction analysis. The emission spectra for [Gd(TTA)₃(TPPO)₂] and [Gd(TTA)₂(NO₃)(TPPO)₂] complexes are associated to T→S₀ transitions centered on coordinated TTA ligands. Experimental luminescent properties of the bis-TTA complex have been quantified through emission intensity parameters Ω_λ (λ=2 and 4), spontaneous emission rates (A_rad), luminescence lifetime (τ), emission quantum efficiency (η) and emission quantum yield (q), which were compared with those for tris-TTA complex. The experimental data showed that the intensity parameter value for bis-TTA complex is twice smaller than the one for tris-TTA complex, indicating the less polarizable chemical environment in the system containing nitrate ion. A good agreement between the theoretical and experimental quantum yields for both Eu(III) complexes was obtained. The triboluminescence (TL) of the [Eu(TTA)₂(NO₃)(TPPO)₂] complexes are discussed in terms of ligand-to-metal energy transfer.     

双光栅白光衍射干涉的消色效应

本文提出和研究了白光点源照明下的双光栅衍射干涉效应,报道了白光照明下剪切干涉的“消色效应”,给出了完整的菲涅耳线性标量衍射原理的数学推导和几何光学的解释.     

Synthesis and luminescent properties of PEO/lanthanide oxide nanoparticle hybrid films

In this study, we investigate the optical properties of lanthanide oxide nanoparticles dispersed in poly(ethylene oxide) (PEO) network as thermally stable polymeric films. The aim of this work is both to keep a good optical transparency in the visible domain and to obtain luminescent materials after incorporation of nanoparticles. For this purpose, we develop luminescent nanocrystals of oxides containing terbium ion as a doping element in Gd₂O₃. These sub-5-nm lanthanide oxides nanoparticles have been prepared by direct oxide precipitation in high-boiling polyalcohol solutions and characterized by luminescence spectroscopy. PEO/lanthanide oxide nanohybrid films are prepared by radical polymerization of poly(ethylene glycol) methacrylate after introduction of lanthanide oxide particles.As a first result; the obtained films present interesting luminescence properties with a very low lanthanide oxide content (up to 0.29 wt%). Furthermore, these films are still transparent and keep their original mechanical properties.Prior to describe the specific applications to optical use, we report here the dynamic mechanical analysis (DMA), X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM), and luminescent properties of. nanohybrid films.     

Second-harmonic generation by elliptic Bessel light beams in periodically polarized nonlinear crystals

The features of the frequency doubling of elliptic Bessel light beams under quasi-synchronous interaction in periodically polarized nonlinear crystals have been investigated. The overlap integrals describing the efficiency of second-harmonic generation by elliptic Bessel light beams have been investigated numerically. Reported at the Vth International Scientific-Technical Conference on Quantum Electronics, November 22–25, 2004, Minsk, Belarus. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 6, pp. 752–755, November–December, 2005.     

Theory of divalent ions in crystals

The divalent ions in alkaline earth chalcogenides are viewed as compressible objects and are treated within a purely ionic model. As in earlier studies on the alkali and ammonium halides, the ions are taken to be in the form of space-filling polyhedral cells and the compression energy, which is the source of repulsion, is written as a surface integral over the cell faces. A simple method of computing the repulsion energy in any crystal lattice of arbitrary symmetry is proposed and the repulsion parametersB andσ are refined for the divalent ions under study. The theory explains the predominant occurrence of the NaCl structure in the alkaline earth chalcogenides. Hard sphere radii are estimated for the tetravalent cations Ti⁴⁺, Sn⁴⁺ and Pb⁴⁺ using the repulsion parameters of O²⁻ ion and the data on the corresponding rutile structure oxides. These radii are seen to be consistent with the measured interionic distances in several compounds occurring in the perovskite structure. The free transfer of repulsion parameters among several structures, which is a key feature of the present approach to repulsion, is confirmed to be valid by the present study.     

White light emitting from single phased K2Ca1−x−yP2O7: xEu, yMn phosphors under UV excitation

A single phased white light emitting phosphors K₂Ca_1−x−yP₂O₇: xEu²⁺, yMn²⁺ were synthesized by solid state reaction method. The Effective energy transfer occurs in this phosphor due to the large spectral overlap between the emission of Eu²⁺ and the excitation of Mn²⁺. The emission hue of K₂Ca_1−x−yP₂O₇: xEu²⁺, yMn²⁺ from blue to white light can be obtained by tuning the Eu²⁺/Mn²⁺ content ratio. The energy transfer mechanism from Eu²⁺ to Mn²⁺ in this phosphor was carefully investigated and demonstrated to be via the dipole–quadrupole interaction.     

Interference of white light in tandem configuration of birefringent crystal and sensing birefringent fiber

Spectral interference of white-light beams propagating through a tandem configuration of birefringent crystal and sensing birefringent fiber is analyzed theoretically and experimentally. The spectral interference law is expressed analytically under the condition of a Gaussian response function of a spectrometer taking into account the dispersion of birefringence in the crystal and in the fiber. Two types of spectral interferograms are modeled knowing dispersion characteristics of the sensing fiber and using a quartz crystal of the positive or a calcite crystal of the negative birefringence. The theoretical analysis is accompanied by two experiments employing a highly birefringent fiber and a birefringent quartz crystal of two suitable thicknesses. Within both experiments the spectral interference fringes are resolved in accordance with the theory with phases dependent on the fiber length.     

A comparative study of the electrodeposition and the aqueous chemical growth techniques for the utilization of ZnO nanorods on p-GaN for white light emitting diodes

Vertically well aligned zinc oxide nanorods (ZnO NRs) were grown on p-GaN by electrodeposition (ED) and aqueous chemical growth (ACG) techniques and the structures were employed to fabricate white light emitting diodes (LEDs). Room temperature current voltage (I–V$I–V$), photoluminescence (PL), and electroluminescence (EL) measurements were performed to investigate and compare both LEDs. In general, the I–V$I–V$ characteristics and the PL spectra of both LEDs were rather similar. Nevertheless, the EL of the ED samples showed an extra emission peak shoulder at 730 nm. Moreover, at the same injection current, the EL spectrum of the ED light emitting diode showed a small UV shift of 12 nm and its white peak was found to be broader when compared to the ACG grown LED. The broadening of the EL spectrum of the LED grown by ED is due to the introduction of more radiative deep level defects. The presented LEDs have shown excellent color rendering indexes reaching a value as high as 95. These results indicate that the ZnO nanorods grown by both techniques possess very interesting electrical and optical properties but the ED is found to be faster and more suitable for the fabrication of white LEDs.     

Luminescent spectroscopy and structure of centers of the impurity Eu ions in lead tungstate crystals

Spectral-luminescent properties of the lead tungstate crystals doped with the Eu³⁺ ions were investigated in a wide temperature range at different excitation and registration wavelengths. The spectra consist of both weak wide nonstructural bands of the matrix emission and narrow spectral lines caused by inner f-f electron transitions in the impurity Eu³⁺ ions. The analysis and interpretation of spectral lines observed in excitation and luminescence spectra have shown formation of at least two different types of luminescent centers on the basis of the Eu³⁺ ions in the PbWO₄ crystals. These two types of centers are considered to be caused by arrangement of the impurity Eu³⁺ ions in Pb sites as well as in W sites of host matrix. For both types of centers values of S² scalar crystal field strength, and crystal field parameters were estimated and local site symmetries were found.     

Ultrasound diffraction of light beams in gyrotropic crystals

The features of the Bragg diffraction of Gaussian light beams at ultrasound waves in gyrotropic crystals were investigated. The dependence of the diffraction efficiency on the intensity of an ultrasound beam, the cross-section radius of a light beam, and their divergence ratio was found. An asymptotic expression for the transverse distribution of a diffracted beam was derived. The crystal gyrotropy has been found to affect significantly the change in the amplitude profile of the diffracted light at ultrasound frequencies of f ∼ 10²–10³ MHz. The maximum diffraction efficiency in the gyrotropic medium is shown to be reached at a certain ratio between the divergences, ultrasound intensity, and specific gyration of the crystal. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 3, pp. 370–374, May–June, 2000.     

Energy loss of light ions in polypropylene absorber foils

The energy loss of Li, C and O ions in polypropylene absorber foils has been measured using 15 UD Pelletron Accelerator facility at Inter University Accelerator Centre (IUAC), New Delhi, India. The actual experiment has been performed in low flux chamber attached to the General Purpose Scattering Chamber (GPSC). These experimental energy loss values have been compared with the computed values based on various empirical/semi-empirical formulations. Some interesting trends have been observed.