Spectroscopic properties and energy transfer in Er–Tm co-doped bismuth silicate glass

In this paper, we investigate the spectroscopic properties of and energy transfer processes in Er–Tm co-doped bismuth silicate glass. The Judd–Ofelt parameters of Er³⁺ and Tm³⁺ are calculated, and the similar values indicate that the local environments of these two kinds of rare earth ions are almost the same. When the samples are pumped at 980 nm, the emission intensity ratio of Tm:³F₄ → ³H₆ to Er:⁴I_13/2 → ⁴I_15/2 increases with increased Er³⁺ and Tm³⁺ contents, indicating energy transfer from Er:⁴I_13/2 to Tm:³F₄. When the samples are pumped at 800 nm, the emission intensity ratio of Er:⁴I_13/2 → ⁴I_15/2 to Tm:³H₄ → ³F₄ increases with increased Tm₂O₃ concentration, indicating energy transfer from Tm:³H₄ to Er:⁴I_13/2. The rate equations are given to explain the variations. The microscopic and macroscopic energy transfer parameters are calculated, and the values of energy transfer from Er:⁴I_13/2 to Tm:³F₄ are found to be higher than those of the other processes. For the Tm singly-doped glass pumped at 800 nm and Er–Tm co-doped glass pumped at 980 nm, the pumping rate needed to realize population reversion is calculated. The result shows that when the Er₂O₃ doping level is high, pumping the co-doped glass by a 980 nm laser is an effective way of obtaining a low-threshold ∼2 μm gain.     

Efficient 1.53 μm emission and energy transfer in Si/Er-Si-O multilayer structure

Strong 1.53 μm light emission has been achieved in Si/Er-Si-O multilayer structure grown by sputtering method and annealing process. The luminescence intensity at 1.53 μm increases with annealing temperature, reaching maximum at about 800 °C, and decreases at higher temperatures. It is found that the amorphous Si well layer can sensitize and enhance Er³⁺ luminescence in Er-Si-O sublayer through carrier-mediated processes. Moreover, the Si/Er-Si-O multilayer exhibits much low temperature- and carrier-induced quenching of Er³⁺ luminescence, with the photoluminescence intensity at 1.53 μm decreased about a factor of only 1.4 from 80 K to 300 K. The new Si nanostructure material reported here may open the route towards the realization of electrically pumped Si-based light source.     

Polarized spectroscopic properties of Ho-doped LuLiF4 single crystal for 2 μm and 2.9 μm lasers

Polarized spectroscopic properties of a Ho³⁺-doped LuLiF₄ (Ho:LuLF) single crystal grown by the Czochralski method have been investigated as a promising material for 2 μm and 2.9 μm lasers. The Judd-Ofelt (J-O) model has been applied to the analysis of the polarized room temperature absorption spectra to establish the so-called J-O intensity parameters. Based on the calculated parameters, we determined the emission probabilities, branching ratio and radiative lifetime for the Ho³⁺ transitions from the excited state manifolds to the lower-lying manifolds. Ho:LuLF crystal shows long fluorescence lifetime of ⁵I₇ manifold (16 ms) and broad absorption and emission spectra, which exhibit strong polarization characteristics. Stimulated emission cross-sections spectra of the ⁵I₆ → ⁵I₇ and ⁵I₇ → ⁵I₈ transitions were derived and compared with those of the other well-known Ho³⁺-doped laser crystals.     

Synthesis and spectral properties of Yb/Ho co-doped yttria 2 μm transparent ceramics

Yb/Ho co-doped yttria transparent ceramics, Yb/Ho:Y₂O₃, were prepared by vacuum sintering with additional 0.5 wt.% tetraethyl orthosilicate (TEOS) as sintering aid from the Yb/Ho co-doped yttria nanopowders synthesized by co-precipitation method. The optical quality of transparent ceramics was improved significantly, as increasing the sintering temperature from 1800 °C to 1850 °C as well as the holding time from 20 h to 25 h, respectively. The absorption spectrum was measured to find out the advisable emission source wavelength. The 2 μm emission bands were observed under laser diode excitation at 980 nm in the co-doped sample with 5 mol% of Yb³⁺ and 1 mol% of Ho³⁺, and broad emission bandwidth were obtained.     

Structural transformation and magnetic properties of CaMn1 − xFexO3 − δ (0.0 ≤ x ≤ 0.5)

We have investigated the structural and magnetic properties of CaMn_1 − xFe_xO_3 − δ (0.0 ≤ x ≤ 0.5). Solid state method is used for the synthesis of these samples. Sintering of these compositions at 1300 °C stabilizes higher ionic radii Fe^+ 3 (0.645 Å) at Mn^+ 4 (0.53 Å) site in CaMn_1 − xFe_xO_3 − δ. Structural transformation from orthorhombic to tetragonal to pseudo cubic crystal system and the increase in lattice parameters have been observed with the substitution of Fe at Mn site in CaMn_1 − xFe_xO_3 − δ (0.0 ≤ x ≤ 0.5). The magnetization data show the transformation of G type of antiferromagnetic arrangement of Mn^+ 4 electrons spins in CaMnO₃ into paramagnetic spin type arrangement with the substitution of Fe at Mn site. The compositions x = 0.05, x = 0.1and x = 0.2 show a small kink ~ 100 K in the magnetization data, which resulted due to the competition between antiferromagnetic and paramagnetic states with the Fe substitution.     

Silicon-rich oxynitride hosts for 1.5 μm Er emission fabricated by reactive and standard RF magnetron sputtering

This study compares the erbium emission from different Si-rich silicon oxynitrides matrices fabricated by magnetron sputtering. The Er-doped layers were grown by two different sputtering configurations: (i) standard co-sputtering of three confocal targets (Er₂O₃, Si₃N₄ and SiO₂) under Ar plasma, and (ii) reactive co-sputtering under Ar + N₂ plasma of either three (Er₂O₃, pure Si and SiO₂) or two targets (Er₂O₃ and pure Si). The last reactive configuration was found to offer the best Er³⁺ PL intensity at 1.5 μm. This highest PL intensity was found comparable to the corresponding emission from Er-doped silicon-rich silicon oxide.     

Preparation and properties of La1 − xAgyMnO3 + δ thin epitaxial films

We report here the preparation and properties of La_1 − xAg_yMnO_3 + δ thin epitaxial films. The original two-step preparation procedure was developed. At first, La_1 − xMnO_3 + δ were grown epitaxially by metal-organic chemical vapor deposition on the single-crystal substrates (001) and (110) SrTiO₃, (001) LaAlO₃, (111) and (001) ZrO₂(Y₂O₃). Treatment by the vapor of the metallic silver in the oxygen atmosphere (at 1 bar and 20 bar) was the second step resulting in the selective absorption of silver by La_1 − xMnO_3 + δ phase. The value of y depended on the process conditions and revealed different kinetics of the silver absorption for (001) and (110) orientation of La_1 − xMnO_3 + δ films. The films prepared were characterized by X-ray diffraction, scanning electron microscopy with energy-dispersion X-ray analysis, high resolution transmission electron microscopy, X-ray photoelectron spectroscopy, electrical resistivity and magnetoresistance measurements in a four-probe configuration. We have found that metal-insulator transition temperature (T_p) in the series La_1 − xAg_xMnO_3 + δ possessed a maximum of 380 K at x = 0.15. Thus, T_p of La_1 − xAg_xMnO_3 + δ films was significantly higher than ever reported in the literature for the La_1 − xAg_xMnO_3 + δ ceramics. La_1 − xAg_xMnO_3 + δ films demonstrated the important role of the ferromagnetic fluctuations above Curie temperature T_c resulting in the sign change of the resistivity curve temperature slope dR / dT and a significant shift of T_p well above T_c. The maximum of the magnetoresistance on the temperature scale was close to dR / dT maximum. The intrinsic magnetoresistance values as high as 22% at 310 K and 50% at 280 K were measured in the magnetic field of 1 T in the series of La_1 − xAg_yMnO_3 + δ epitaxial films.     

(0 0 6)-oriented α-Al2O3 films prepared in CO2-H2 atmosphere by laser chemical vapor deposition using a diode laser

(0 0 6)-oriented α-Al₂O₃ films were prepared by laser chemical vapor deposition (LCVD) using aluminum acetylacetonate (Al(acac)₃) in CO₂-H₂ atmosphere. The effects of the CO₂ mole fraction (FCO₂) and laser power (P_L) on the crystal phase, microstructure, and deposition rate (R_dep) were investigated. α- and γ-Al₂O₃ mixture films were prepared at P_L = 90 W (deposition temperature of 818 K), whereas (0 0 6)-oriented single-phase α-Al₂O₃ films were obtained at P_L = 110 W (863 K). The texture coefficient and the grain size of the (0 0 6)-oriented films increased with increasing FCO₂. The orientation of the α-Al₂O₃ films changed from (0 0 6) to (1 0 4) to (0 1 2) with increasing P_L (T_dep). The R_dep of the (0 0 6)-oriented α-Al₂O₃ films increased with increasing FCO₂.     

Cw and passively Q-switched laser performance of a mixed c-cut Nd:Gd0.33Lu0.33Y0.33VO4 crystal operating at 1.34 μm

Continuous wave and passively Q-switched laser operation with a mixed c-cut Nd:Gd_0.33Lu_0.33Y_0.33VO₄ crystal at 1.34 μm has been realized for the first time as far as we know. The largest output power of the continuous wave was 1.1 W for the output mirror of 5% transmission, with the optical conversion efficiency and the slope efficiency being 15% and 17.2%, respectively. The passive loss and the stimulated emission cross-section of the Nd:Gd_0.33Lu_0.33Y_0.33VO₄ crystal were found to be 0.6% and 0.47 × 10⁻¹⁹ cm². The thermal lens effect that weakened the laser performance has also been measured. For passively Q-switched operation, the shortest pulse duration of 26 ns, the highest peak power of 1.8 kW, along with the pulse energy as large as 47 μJ, were obtained using V:YAG as Q-switch. The experimental results have shown that the passively Q-switched Nd:Gd_0.33Lu_0.33Y_0.33VO₄ laser can generate pulses with larger pulse energy and higher peak power in comparison with the passively Q-switched Nd:GdYVO₄ lasers.     

Evaluation of free carrier losses to 1.54 μm emission in Si/Si:Er nanolayers on SOI substrate for optical gain observation

In this study we use a combination of variable stripe and shifting excitation spot methods to evaluate linear low temperature (4.2 K) optical properties of Si/Si:Er multinanolayer grown on SOI substrate. In particular, Er-1 luminescence at 1.54 μm under continuous wave excitation was examined. Absorption coefficients of 22.4 ± 4.2 and 45.1 ± 4.2 cm⁻¹ at photon fluxes of 2.4 × 10¹⁹ and 2.4 × 10²⁰ cm² s⁻¹, respectively, have been established. These are approximately three times higher than those found earlier for a similar structure grown on Si substrate.     

Sol–gel synthesis,characterization and luminescent properties of Tb doped MLa2O4 (M = Sr or Ba) nanophosphors

Tb³⁺ doped SrLa₂O₄ and BaLa₂O₄ nanophosphors were successfully synthesized via tartaric acid assisted sol–gel method and their luminescent properties were investigated. The crystal structure and morphology of SrLa₂O₄:Tb³⁺ and BaLa₂O₄:Tb³⁺ was studied by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). Thermal decomposition behavior of the dried gels was investigated by thermogravimetry (TG) and differential thermal analysis (TGA). Photoluminescence (PL) behaviors of these nanophosphors were checked by the excitation and emission spectra. These SrLa₂O₄ and BaLa₂O₄ nanophosphors displayed green color under a UV source due to characteristic transition of Tb³⁺ from ⁵D₄ → ⁷F₅ at 544 nm. The dependence of photoluminescence intensity on Tb³⁺ ion concentration, tartaric acid concentration and annealing temperature were also studied in detail. In addition, the optimum doping concentration and time-resolved luminescence spectroscopy were also investigated.     

2 μm emission properties and hydroxy groups quenching of Tm3+ in germanate-tellurite glass

Tm³⁺ activated germanate-tellurite glasses with good thermal stability and anti-crystallization ability were prepared. Efficient 2 μm fluorescence was observed in the optimal concentration Tm³⁺ doped glass and the corresponding radiative properties were investigated. For Tm³⁺: ³F₄ → ³H₆ transition, high spontaneous radiative transition probability (260.75 s⁻¹) and large emission cross section (7.66 × 10⁻²¹ cm²) were obtained from the prepared glass. According to Dexter's and Forster's theory, energy transfer microscopic parameters were computed to elucidate the observed 2 μm emissions in detail. Besides, the effect of hydroxy groups quenching was also quantificationally investigated based on simplified rate equations. Results demonstrate that the optimal concentration Tm³⁺ doped germanate-tellurite glass possessing excellent spectroscopic properties might be an attractive candidate for 2 μm laser or amplifier.     

Fast dynamics of 1.5 μm photoluminescence in Er-doped SiO2 sensitized with Si nanocrystals

In order to investigate origin of fast photoluminescence at 1.5 μm reported to appear in Er-doped SiO₂ sensitized with silicon nanocrystals, time-resolved photoluminescence measurements were compared between high temperature annealed Er-doped and Er-free samples. We confirm that this fast photoluminescence band observed in our materials is due to radiative recombination of Er³⁺ ions. At low temperatures, also a contribution from defect related-emission centered around 1300 nm appears and adds up to the Er-related emission.     

Crystal growth and characterization of Ho-doped Lu3Ga5O12 for 2 μm laser

Ho:LuGG single crystal was successfully grown by the Czochralski growth method, and its lattice parameter was found to be 12.2371 Å. Its thermal conductivity was measured to be 5.29 W mK⁻¹ at 300 K. Meanwhile, transmission spectra were recorded at room temperature, and then its absorption spectra were obtained combining with the transmission spectra of LuGG crystal. The transition intensity parameters Ω_t (t = 2, 4, 6), the oscillator strengths, fluorescence branching ratios, transition probabilities and the lifetimes of Ho³⁺ in LuGG crystal were all evaluated by the Judd–Ofelt theory. Furthermore, its emission spectra were also determined and analyzed.     

Electrical characterisation of p-doped distributed Bragg reflectors in electrically pumped GaInNAs VCSOAs for 1.3 μm operation

The high resistivity that is encountered in p-type DBRs is an important problem in vertical cavity surface emitting lasers and optical amplifiers (VCSELs and VCSOAs). This is because the formation of potential barriers at the interfaces between layers of high and low refractive index inhibits the carrier flow, thus increasing the DBR series resistance. In this work, the electrical characteristics of two p-type doped DBR structures grown on undoped and p-type doped GaAs substrates have been investigated. The DBRs are designed for VCSOAs operating at 1.3 μm and consist of 14-periods of alternating GaAs and Al_0.9Ga_0.1As in the first sample and 14-periods of GaAs and Al_0.3Ga_0.7As/Al_0.9Ga_0.1As in the second one. For the longitudinal transport sample, Hall mobility and sheet carrier density were measured in the temperature range from 77 to 300 K. In the vertical transport sample, current–voltage (I–V) measurements across the DBR layers were carried out at different temperatures in the range between 15 and 300 K. We achieved resistivity reduction in our samples by using an interface composition grading technique aimed at improving the VCSOA characteristics.     

Inhibition action of thiosemicabazone and some of it is ρ-substituted compounds on the corrosion of iron-base metallic glass alloy in 0.5 M H2SO4 at 30 °C

The study of the effect of thiosemicarbazone compounds on the corrosion of the iron-base Fe₈₁B_13.5Si_3.5C₂ metallic glass in 0.5 M H₂SO₄ solutions by electrochemical technique shows that these compounds were very effective inhibitors, their protection percentage exceeded 98% at low concentrations as much as 10⁻⁴ M. A mixed type of inhibition from polarization and a charge transfer mechanism from impedance study in absence and presence of these compounds were found. Langmuir adsorption isotherm is obtained. Linear free energy relationships (LFER) have used to correlate the protection percentage of thiosemicarbazone and it is ρ-substituted derivatives with the Hammett substitute constant (σ). The value of ρ = +0.328 indicates weak dependence of the substitution on the adsorption character of the reaction center. The reactivity of these compounds was analyzed through theoretical calculations based on density functional theory to confirm that () is the reactive center. The effect of immersion time at certain concentration was studied.     

Polarized spectral properties and 1.5–1.6 μm laser operation of Er:Sr3Yb2(BO3)4 crystal

Undoped and Er³⁺-doped Sr₃Yb₂(BO₃)₄ crystals were grown by the Czochralski method. Room temperature polarized spectral properties of the Er:Sr₃Yb₂(BO₃)₄ crystal were investigated. The efficiency of the energy transfer from Yb³⁺ to Er³⁺ ions in this crystal was calculated to be about 95%. End-pumped by a diode laser at 970 nm in a hemispherical cavity, a 0.75 W quasi-CW laser at 1.5–1.6 μm with a slope efficiency of 7% and an absorbed pump threshold of 3.8 W was achieved in a 0.5-mm-thick Z-cut crystal glued on a 5-mm-thick pure YAG crystal with UV-curable adhesive.     

Dielectric properties,thermal expansion and heat capacity of (1 − x)Na0.5Bi0.5TiO3–xBaTiO3 single crystals (x = 0, 0.02, 0.025, 0.0325 and 0.05)

High-quality and large-size lead-free (1 − x)Na_0.5Bi_0.5TiO₃–xBaTiO₃ single crystals (x = 0, 0.025, 0.0325 and 0.05) were grown using Czochralski method. The obtained samples were of pure perovskite structure with rhombohedral symmetry at room temperature. Thermal expansion, heat capacity, ferroelectric and dielectric properties were measured in a wide temperature range. The broad anomalies observed in thermal expansion and heat capacity were corresponded to structural, ferroelectric and dielectric anomalies, related to temperature features of polar regions and formation of a long-range order ferroelectric phase. The Burns temperature was found to increase with increasing BaTiO₃ content. At low-frequency (100 Hz–100 kHz) the samples showed diffuse phase transitions. The obtained results were discussed in terms of local electric and strain fields caused by a difference in ionic radii between (Na,Bi) and Ba ions.     

A comparative study of Pr substitution at Y and Ba sites in YBa2Cu3O7 − δ

Aimed at identifying the factors which suppress the superconductivity in cuprate perovskites I have investigated the effect of substituting Pr ions at the Y and Ba sites in YBa₂Cu₃O_7 − δ system using structural, transport, iodometric, and photoemission studies. The rate of Tc depression in the case when Pr substitutes the Ba site is much higher than the case when it substitutes the Y. This is explained as being due to a combined effect of the factors such as depletion of itinerant holes due to depletion of the oxygen content, the Pr 4f-O 2p hybridization, shortening of c-axis causing Cooper pair-breaking, and the loss of orthorhombicity.