Yttrium Gallium Research Articles

Structure–property correlations in Ce-doped garnet phosphors for use in solid state lighting

The discovery of inorganic phosphors that can be excited by GaN light emitting diodes in the wavelength range 380–460 nm is essential for improving the efficiency and light quality of solid state lighting devices. Garnets doped with Ce 3+ are of particular interest for this application. We have studied the luminescence of Ce 3+ in garnet phosphors and established a relationship between the excitation/emission wavelengths and the deviation from cubic symmetry around the rare-earth ion. Data are presented for both known yttrium aluminum and yttrium gallium garnet systems, as well as newly synthesized inverse garnets of the general formula Mg 3Y 2− y Gd y Ge 3− z Si z O 12:Ce (0 ⩽ y ⩽ 2, z = 0, 1).

Preparation and characterization of yttrium gallium garnet nanoparticles by citrate sol–gel method at low temperature

The Y 3Ga 5O 12 (YGG) nanoparticles with pure phase have been successfully prepared with Y(NO 3) 3 and Ga 2O 3 at lower sintering temperature and shorter holding time. The process of citrate sol–gel method was simple and the cost was very low. The thermal behavior of the YGG precursor was characterized by thermogravimetry/differential thermal analysis (TG/DTA). The crystallization temperature was determined by X-ray powder diffraction (XRPD). The morphology of the particles was characterized by transmission electron microscope (TEM). The results illustrate that the crystallization temperature of YGG nanoparticles was about 700 °C and the powders made by this method dispersed uniformly.

EPR theoretical study of local lattice structure of Fe 3+ in octahedral site in yttrium gallium garnet

By analyzing the EPR parameters D and ( a− F) of Fe 3+ ion located at octahedral site in yttrium gallium garnet, the local lattice structure around Fe 3+ ion in the crystal has been investigated on the basis of the complete energy matrices for a d 5 configuration ion in a trigonal ligand field. It is shown that there exists a slight expansion distortion in the local lattice structure and the distortion is different at 4.2 and 295 K. This result may be attributed to the fact that the radius of Fe 3+ ion is larger than that of Ga 3+ ion, and the Fe 3+ ion will push the two oxygen triangles to move upwards and downwards, respectively, along C 3-axis when the temperature decreases. From EPR calculation, the local lattice structure parameters R = 2.0068 Å, θ = 51.4691 ° at 295 K and R = 2.010 Å, θ = 51.3706 ° at 4.2 K for octahedral Fe 3+ centre in yttrium gallium garnet are determined.

Low-temperature synthesis and characterization of yttrium–gallium garnet Y 3Ga 5O 12 (YGG)

To obtain yttrium–gallium garnet (Y 3Ga 5O 12, YGG) a simple “chimie douce” method has been developed. This sol–gel method yielded excellent starting gel precursor for the fabrication of YGG phase, which could be used as host material for optical applications. The pattern of X-ray diffraction analysis of the ceramic sample sintered for 10 h at 1000 °C showed the formation of monophasic Y 3Ga 5O 12 phase. The phase transformations, composition and micro-structural features in the gels and polycrystalline sample were studied by thermoanalytical methods (TGA/DTA), powder X-ray diffraction analysis (XRD), infrared spectroscopy (IR) and scanning electron microscopy (SEM). The quality of the resulting products (homogeneity, crystallisation temperature, grain size, grain size distribution, etc.) is discussed.

Attribution of the absorption bands of ruthenium-doped yttrium gallium garnet crystals to Ru3+, Ru4+, and Ru5+ 4d-ions by MCD

Abstract Ruthenium-doped yttrium gallium garnet single crystals were grown from a PbO/PbF2/B2O3 flux. Most samples are blue, occasionally green, orange or lemon yellow, depending upon the growth temperature and the amount of a divalent or tetravalent counterion. A spectroscopic study was carried out using several complementary techniques (optical absorption, MCD, and EPR). Low temperature MCD enabled discrimination among those absorption bands correlated to paramagnetic ions (Ru3+ or Ru5+) or diamagnetic Ru4+ at the octahedral site. Ru3+ dominates in the lemon yellow sample with a nominal Ge/Ru ratio of ≈7, whereas Ru5+ is responsible for the orange colour in a crystal with Ca/Ru ≈7. The strongest MCD features above 2.2 eV could be rationalised in terms of oxygen-to-Run+ (n = 3–5) charge transfer transitions in octahedral complexes, whereas the 2 eV band of blue crystals is tentatively assigned to an intervalence transition implying Ru4+. It is suggested that YIG films co-doped with ruthenium and a large amount of calcium or germanium might present interesting Faraday effect properties.

X-ray and optical studies of ytterbium-doped gallium garnets

Single crystals of yttrium gallium and lutetium gallium garnets doped with ytterbium were grown from the melt by Czochralski technique. Comparison is made between the lattice spacing of ceramic and single crystals to estimate the degree of octahedral ytterbium substitution. When heated to around 1200°C under reducing atmosphere the yttrium gallium garnet crystal acquires violet color due to appearance of additional absorption bands. Displacements of absorption bands as a function of the average radius on the dodecahedral site resemble those observed in aluminum garnets and generally considered as associated with divalent ytterbium. Basing on X-ray calibration, the peak positions of induced absorption bands can be used to estimate the dodecahedral concentration of ytterbium in the crystal. Charge transfer luminescence properties were studied in LuGG:Yb crystals.

Ion Beam Sputter-Fabrication of Bi–YIG Films for Magnetic Photonic Applications

We report the fabrication of polycrystalline and epitaxial Bi-substituted yttrium gallium iron garnet films on amorphous oxide coated Si wafers and single crystalline gadolinium gallium garnet (GGG) substrates for potential magnetic photonic device applications via reactive ion beam sputtering of a single phase (Bi/sub 0.8/Y/sub 2.2/)(Ga/sub 1/Fe/sub 4/)O/sub 12/ target. The observed Bi-YIG film magnetic properties are sensitive to sputtering parameters like the reactive molecular oxygen ion or radical neutral oxygen atom flux substrate impingement, and the specular or nonspecular geometry control of the reflected neutral substrate bombardment. Nonferrimagnetic amorphous Bi-YIG films are obtained using the specular sputtering geometry that can be recrystallized as randomly oriented single-phase YIG films with in-plane anisotropy using post-deposition rapid thermal annealing (RTA). Also, nonspecularly sputtered Bi-YIG films with improved interfaces and weak nanocrystallinity can be fabricated, yielding "as grown" ferrimagnetic behavior that can be further improved by RTA. Epitaxial Bi-YIG films on GGG with extremely soft magnetic characteristics and strong in-plane anisotropy have also been fabricated.

Crystal growth of Yb 3+-doped oxide single crystals for scintillator application

Long emission wavelength scintillators are strongly required from the viewpoint of the practical use of silicon photo-diode, which has higher resolution with lower cost compared with photo-multipllier. Among the various scintillator emission centers, we regard emission from Yb 3+ charge-transitions state (CTS) as a candidate. In order to investigate proper hosts for Yb 3+ CTS, the yttrium gallium garnet host and lutetium aluminum garnet host were studied. Transparent and crack-free heavily Yb-doped YGG, i.e. {Y 1− x Yb x } 3[Ga] 2(Ga) 3O 12 (Yb: YGG, x=0.15, 0.5, 1.0) and heavily Yb-doped LuAG, i.e. {Lu 1− x Yb x } 3[Al] 2(Al) 3O 12 (Yb: LuAG, x=0.15, 0.5, 1.0) single crystals could be grown by the Modified Pulling Down method with 〈1 1 1〉 orientation. Emission, excitation spectra and decay kinetics were measured for these crystals. The CT transition of Yb 3+ in the yttrium gallium garnet host was discussed compared with the Yb 3+ one in the lutetium aluminum garnet host.

Evaluation of the parameters of cation distribution in Y3A5−z B z O12 solid solutions

Crystal chemical models are proposed for describing the regularities in the distributions of ions and point defects in solid solutions of yttrium aluminum, yttrium gallium, and yttrium iron garnets. The concentration dependences of the distributions of ions and point defects in solid solutions are evaluated in terms of multidimensional nonlinear optimization.

Spectroscopy and Continuous Wave Near-Infrared Stimulated Emission of New Yttrium Gallium Garnet {Y3}[Y, Ga](Ga3)O12:Nd3+ (YGaO3:Nd3+)

Detailed spectroscopic investigations are made for a new laser material, a Nd3+-ion doped YGaO3 garnet crystal with disordered structure, grown from the physicochemical Y2O3-Ga2O3 system with sesquioxide relation close to 1:1. Following absorption and luminescence spectral analyses, the Stark splitting of the 4F3/2 and 4Ij’ manifolds of Nd3+ activators are measured with high accuracy. Between the Stark levels of two near-infrared laser channels (4F3/2→4I11/2 and 4F3/2→4I13/2) low-threshold continuous wave stimulated emission was excited at 300 K. Some spectroscopic characteristics, such as radiative lifetime of the initial laser 4F3/2 state, intermanifold and inter-Stark luminescence branching ratios, linewidths, spontaneous transition probabilities and peak and effective cross-sections of induced transitions are also determined. These parameters are necessary for a theoretical description of the functional properties of Nd3+:YGaO3 lasers.

Selectively excited luminescence and magnetic circular dichroism ofCr4+-doped YAG and YGG

Site selective luminescence and magnetic circular dichroism experiments on ${\mathrm{Cr}}^{4+}$-doped yttrium aluminum garnet and yttrium gallium garnet have been made at low temperature. The spectral assignments for these near-IR lasing materials have been made using experimental data and ligand field calculations guided by the known geometry of the lattices.

Temperature dependent EXAFS measurements on YGG during a sol-gel process

Temperature dependent X-ray absorption spectroscopy has been used as a local probe to elucidate the structure of yttrium gallium garnet produced by a sol-gel route. The treatment of our experimental data includes a cumulant expansion analysis taking into account the asymmetry of the pair distribution function resulting from disorder at high temperature.

Infrared spectroscopy of yttrium aluminum, yttrium gallium, and yttrium iron garnets

All 17 infrared lattice modes for yttrium aluminum, yttrium gallium, and yttrium iron garnets Y3R2(RO4)3 are obtained from single-crystal reflection and absorption spectroscopy, and the powder technique. Assignments for 12 modes are firmly establish based on chemical substitution among these garnets and within related series. Frequencies of the modes associated with translation of yttrium are nearly constant across the series. Frequencies of all other modes decrease quasilinearly as cell volume increases. Values the high and low frequency dielectric constants are in good agreement with independent measurements; also, the Lyddane–Sachs–Teller relationship was found to hold. Calculations of bulk moduli from vibrational spectra using a modification of Brout’s formula linearly correlate with experimental values for KT.

Crystal-field theory and the S-state splitting of Fe3+ in yttrium gallium garnet.

Calculating the S-state splitting of a ${\mathit{d}}^{5}$ ion (${\mathrm{Fe}}^{3+}$, ${\mathrm{Mn}}^{2+}$) in a crystal has been a long-standing difficult problem since 1934 when it was discussed by Van Vleck and Penney. Low and Rosengarten have concluded that crystal-field theory is not capable of providing a unified interpretation for the spectrum and for the S-state zero-field splitting of ${\mathit{d}}^{5}$ $^{6}$S ions. In the present paper, by utilizing a method of combined perturbation composed of the electrostatic, crystal-field, and spin-orbit-coupling energies, and by diagonalizing a set of complete energy matrices constructed for a ${\mathit{d}}^{5}$ configuration and having a total order of 252, a reasonable interpretation is obtained for the d-d spectrum and the EPR cubic zero-field splitting of ${\mathrm{Fe}}^{3+}$ ions located at octahedral and tetrahedral sites in yttrium gallium garnet. This shows that crystal-field theory is as well suited for application to ${\mathit{d}}^{5}$ ions and to other ${\mathit{d}}^{\mathit{n}}$ ions and that the earlier Low-Rosengarten conclusion is wrong. It is also shown that contributions to the ground-state splitting arising from various excited states of the ${\mathit{d}}^{5}$ configuration or from various components of the crystal field do not obey a linear-superposition rule. In the Appendix, a detailed explicit description of the matrices is given.

TRANSFER CHARACTERISTICS OF NONRADIATIVE ENERGY FROM Tb3+ TO Ce3+ IN YTTRIUM GALLIUM GARNETS

Selection-excited spectra and fluorescence lifetimes of Tb3+ and Ce3+ ions in yttrium gallium garnets are obtained at room temperature. In Y3Ga5O12:Tb, Ce, Tb3+ (donor) emission spectrum and Ce3+( acceptor) excitation spectrum overlaps considerably. The observed fluorescence lifetimes of Tb3+ 5D3 and 5D4 levels decrease with Ce3+ concentration when the sample of Y3Ga5O12: Tb, Ce are excited by UV laser pulse. The mechanisms for nonradiative energy transfer from 5D3 and 5D4 states of Tb3+ to 2D3/2 state of Ce3+ are found to be electric dipole-dipole interaction. The critical distance, rate and efficiency of energy transfer from Tb3+ to Ce3+ ion are obtained. The average critical transfer distance (R0) for 5D3 and 5D4(Tb3+)→2D3/2(Ce3+) are 16.3 ? and 11.2 ?, respectively. Although the energy transfer from the 5D4 state is dominated by dipole-dipole interaction, the dipole-quadrupole interaction must also be considered.

Photoluminescence of Cr 3+ ions in RF-sputtered YGG thin films

This paper reports measurement of the R-line and 4T 2→ 4A 2 emission spectra of Cr 3+ ions in RF-sputtered yttrium gallium garnet (YGG) thin films. The variation of the shape of the R-line and its vibronic sideband with composition of the YGG thin film is discussed.

Reflectivity in yttrium iron garnet between 4 and 30 eV using synchrotron radiation

The optical reflectivity at 300 K in yttrium iron garnet YIG between 4 and 30 eV was measured using synchrotron radiation spectroscopy. By means of the Kramers-Kronig analysis and with the aid of the results of previous reflectivity experiments the spectra of complex permittivity e′, e′ and of the optical constants (n, k) were obtained in the range from 2 to 30 eV. The results are compared with those published by Galuza et al. [Fiz. Tverd. Tela15 (1973) 585 and17 (1975) 2863]. A good agreement with their YIG spectra is found. However, by virtue of the continuous synchrotron radiation source the present spectra reveal more details and cover a broader spectral range. A close analogy between YIG and non-magnetic yttrium gallium garnet spectra is observed above 6 eV.

Czochralski crystal growth and aluminum segregation coefficient in yttrium gallium aluminum garnet

The aluminum distribution coefficient and the amount of octahedral yttrium aluminum gallium garnet single crystals obtained by the Czochralski method have been determined from lattice constant variations during crystal growth. The value of the aluminum distribution coefficient was close to 2 for those parts of the crystal with a convex solid-liquid interface and it was close to 1 for those with a flat 〈111〉 solid-liquid interface. The large difference between these values can be explained by chemical stresses in the crystal in the meltback region and small changes of the lattice constant in the part of crystal with a flat 〈111〉 solid-liquid interface. Single crystals of yttrium aluminum gallium garnet with a lattice constant appropriate for LPE film growth of yttrium gallium garnet have been grown.

Luminescence properties of Tb-activated yttrium gallium garnet phosphors

Comparison of luminescence properties between electron-excited and uv-excited yttrium gallium garnet: Tb phosphors is reported. Although the thermoluminescence and phosphorescence in both cases are quite alike once traps are filled, an apparent difference in the behavior of trap filling has been observed. Small addition of V 2O 3 to these phosphors revealed a unique effect on luminescence properties either with the electron excitation or with the uv excitation.

Magnetostatic volume wave propagation in multiple ferrite layers

The dispersive charcteristics of forward and backward magnetostatic waves (MSWs) propagating in single and multiple layer yttrium iron garnet (YIG) and gallium substituted YIG films have been investigated theoretically and experimentally. The theory predicts that the multiple layer structures can support MSW modes corresponding to propagation in the individual layers as well as a composite mode linking the magnetic films. Each mode of propagation has been observed experimentally. The composite mode is excited if the film with the lower value of 4 πM is in contact with the shorted electrode transducers, while single layer modes are excited if the film sequence is reversed. The dispersion of the composite mode can be made approximately linear with proper selection of film thickness.