Active Ion Concentration Research Articles

Bright upconversion emission of Nd 3+ in LiLa 1−xNd xP 4O 12 nanocrystalline powders

Upconversion emission of Nd 3+ doped LiLa 1− x Nd x P 4O 12 nanocrystals powders upon irradiation with 808 nm laser diode has been investigated. This emission of bright orange color was dependent on concentration and excitation incident light intensity. It was found that this emission was threshold phenomenon characterized by long build-up times which were dependent on energy of upconversion emission, concentration of active ions, size of nanocrystalline grains and power of incident light. The mechanism of observed upconversion was discussed in terms of thermally stimulated avalanche process. The emission intensity bistability of upconversion emission was demonstrated.

Effect of the active-ion concentration on the lasing dynamics of holmium fibre lasers

The lasing dynamics of fibre lasers with a core based on quartz glass doped with holmium ions to concentrations in the range of 1019-1020 cm-3 is investigated. It is shown that fibre lasers with a high concentration of active holmium ions generate pulses, but a decrease in the holmium concentration changes the lasing from pulsed to cw regime. At the same time, a decrease in the active-ion concentration and the corresponding increase in the fibre length in the cavity reduce the lasing efficiency.

Effect of high pressure on photoluminescence properties of Eu 3+: K–Ba–Al–fluorophosphate glasses

The effect of hydrostatic pressure and active ion concentration on the luminescence spectra and lifetimes of Eu 3+-doped P 2O 5–K 2O–BaO–Al 2O 3–KF glasses have been studied up to 44.8 GPa at room temperature. The 5 D 0 → 7 F 0–3 transitions exhibit pressure induced red-shift with different magnitudes. The crystal-field (CF) strengths at ambient condition are 338, 332 and 350 cm −1 for 0.05 mol%, 2.0 mol% and 6.0 mol% Eu 2O 3-doped glasses, respectively. These values slowly increase with increasing pressure and finally reach 518, 410 and 381 cm −1 at the highest pressure. The observed increase in the CF strength parameter is found to have an almost cubic dependence on pressure. The luminescence intensity ratio, 5 D 0 → 7 F 2/ 5 D 0 → 7 F 1, of the Eu 3+ ions is found to decrease with increasing pressure. The decay curves follow single exponential nature for all the three concentrations of Eu 2O 3-doped glasses for the entire pressure range studied.

Effect of dysprosium active ions on spectral properties of KGW single crystals

Dysprosium (Dy) doped potassium gadolinium tungstate single crystals were grown by top seeded solution growth using K 2WO 4 as solvent. Two different concentrations of laser active ions were doped in the crystal. Crystals grown with lower growth rate using K 2WO 4 as solvent yielded better quality than that grown by K 2W 2O 7 as solvent. Growth conditions, like cooling rate and the rotation rate were optimized. Absorption studies confirm dominant absorption peaks in the visible as well as in near infrared regions. Photoluminescence reveals a strong yellow emission for the doped samples and the emission intensity of 3% Dy doped sample is 1.4 times higher than that of 1% Dy concentration in KGW. Raman spectra indicate the characteristic vibrational modes corresponding to the tungstate anion. The intensity of peaks in Raman spectra are increased with increase in concentration of Dy, in addition to a slight shift in Raman frequency.

Effect of active-ion concentration on holmium fibre laser efficiency

We have measured the fraction of holmium ions that relax nonradiatively to the ground level as a result of interaction at a metastable level in optical fibres with a silica-based core doped with holmium ions to 2 × 1019 — 2 × 1020 cm-3. The percentage of such ions has been shown to depend on the absolute active-ion concentration. The fibres have been used to make a number of 2.05-μm lasers, and their slope efficiency has been measured. The laser efficiency decreases with increasing holmium concentration in the fibres

Nano/micro-scaled La(1,3,5-BTC)(H 2O) 6 coordination polymer: Facile morphology-controlled fabrication and color-tunable photoluminescence properties by co-doping Eu 3+,Tb 3+

Nano/micro-sized coordination polymer La(1,3,5-BTC)(H 2O) 6 with controllable morphologies have been successfully prepared on a large scale via a simple solution phase method at room temperature. By rationally adjusting the synthetic parameters such as concentration, molar ratio of reactants, surfactant, and solvent, the La(1,3,5-BTC)(H 2O) 6 with 3D flowerlike, wheatearlike, spherical, sheaflike, taillike, bundlelike hierarchical architectures, and 1D nanorods can be selectively prepared. More interestingly, the photoluminescence color of codoped Eu 3+ and Tb 3+ lanthanum 1,3,5-benzenetricarboxylate phosphors can be easily tuned from red, orange, yellow, green-yellow to green by changing co-doping concentration of activator ions, making the material has potential applications in building minioptoelectronic devices, biomedicine, and color display fields.

Modeling of Tunable Luminescence in Multiple Rare Earth Co-Doped Glasses

As luminescence from co-doping systems is highly sensitive to the glass host and concentration of active ions due to complicated electronic transitions within respective active ions and complex energy transfer between them, it is desirable to develop a theoretical model to design and optimize the co-doping system before the fabrication and measurement of the sample. In this paper, we present a numerical approach to model the generation of tunable visible luminescence in multiple rare earth co-doped glasses. According to our research, a glass system with a special combination of Tb3+, Sm3+ and Dy3+ ions can emit tunable luminescence. When glasses co-doped with proper doping concentration of Tb3+ /Sm3+ /Dy3+ ions are excited by different wavelength in the range of 370-410 nm, the luminescent color can be tuned from yellowish white to orange-red. Our work suggests that the tunable luminescence from multiple rare earth co-doped glasses could have further application in colorful light emitting and other display devices.

Spectroscopic investigations of Cd 0.25Gd 0.50□ 0.25WO 4:Eu 3 + — A new promising red phosphor

Novel red-emitting phosphors scheelite-like tungstates of the formula Cd 0.25Eu 0.50□ 0.25WO 4 and Cd 0.25Gd 0.50□ 0.25WO 4:Eu 3+ doped phases with a wide concentration range of the Eu 3+ ion (0.5, 1, 5, 10 mol%) were prepared. Their photoluminescence properties under ultraviolet–visible (UV) as well as under vacuum-ultraviolet–visible (VUV) excitation were studied in detail. The excitation into the ligand-to-metal charge-transfer (LMCT) states (O → W at 275 nm and O → Eu 3+ at 315 nm) led to blue-green emission. All samples could be efficiently excited by the UV light (315 as well as 395 nm) resulting in strong red emission. The emission color of prepared phosphor depended on the active ions concentration. The optical properties suggest that Cd 0.25Gd 0.50□ 0.25WO 4:Eu 3+ could be an efficient red-emitting phosphor for white-light-emitting diodes (WLEDs) applications. The shape of the EPR spectra suggested a local low symmetry environment of Gd 3+ sites in the investigated samples. Only samples with enough large concentration of Gd 3+ ions revealed strong antiferromagnetic interactions with the Curie–Weiss temperature parameter, e.g., Θ = − 25.6 K (10 mol% Eu 3+). A change in the magnetic interaction type with a change in the nominal Eu 3+ concentration indicates possible limits of the concentration quenching phenomenon observed in the same range of the Eu 3+ concentration in optical spectra.

Enhanced luminescence of Tb3 + due to efficient energy transfer fromCe3 + in ananocrystalline Lu2Si2O7 host lattice

Nanocrystalline lutetium pyrosilicateLu2Si2O7 (LPS) doped withTb3 + (LPS:Tb) orCe3 + /Tb3 + (LPS:Ce, Tb) was obtainedat 1250 °C by the reactionof nanostructured Lu2O3 and colloidal SiO2. X-ray diffraction analysis confirmed the crystallization of a single phase of LPS at the indicatedtemperature. Different concentrations of active ions allowed us to study the influence ofCe3 + co-dopingon Tb3 + emission. Tb3 + -doped LPS yields both the blue emission (J = 3, 4, 5, 6) and the green emission (J = 3, 4, 5, 6) ofTb3 + . The greenemission of Tb3 + is enhanced remarkably in both the cathodoluminescence andphotoluminescence spectra because of energy transfer fromCe3 + toTb3 + ions, both of which are present in the host lattice. Based on theoptical luminescence and luminescence excitation spectra, the optimalTb3 + doping level for maximum light output was established to be 9 mol% and the highest enhancement ofTb3 + luminescence byCe3 + co-doping was detectedusing a 1:3 ratio of Ce3 + /Tb3 + concentration. Two different crystallographic sites ofTb3 + in the LPS lattice were detected in the luminescence and excitation spectra of samples with higherTb3 + concentrations (6–9 mol%). The single-exponential decay profile of 5D4 emission for the less concentrated samples and the double-exponential decay for the higherdoping level are in agreement with this observation. Calculation of colour coordinatesshows that LPS:Ce(0.25%)Tb(3%) emits white light.

Facile and rapid fabrication of metal–organic framework nanobelts and color-tunable photoluminescence properties

Novel one-dimensional terbium 1,3,5-benzenetricarboxylate nanobelts have been synthesized on a large scale through direct precipitation in solution phase without the assistance of any surfactant, catalyst, or template. The as-obtained nanobelts present crystallinity in spite of the moderate reaction conditions, exhibiting 1D helical strands and a 3D network framework. The influence of the reaction temperature, concentration, molar ratio of reactants, and solvent on the belt-like nanostructure has been discussed in detail. A possible mechanism based on the crystal structure of the compound is proposed to account for the formation of the nanobelts. A detailed investigation of the photoluminescence of Tb(1,3,5-BTC)(H2O)·3H2O nanobelts indicates that the optical properties of these phosphors are dependent on their size. More interestingly, the luminescence color of the Tb(1,3,5-BTC)(H2O)·3H2O:Eu3+ nanobelts can be easily tuned from green to green-yellow, yellow, orange and red-orange due to the energy transfer from the Tb3+ to Eu3+ ions by changing the doping concentration of activator ions.

Modeling Multiple Rare Earth-Doped System for White Light Generation

A numerical model of Tm3+-Tb3+-Eu3+ -co-doped system for white light generation is presented in this paper. The energy level, electron transition process and rate and power propagating equations are proposed to calculate fluorescence intensity of the system pumped by 359 nm laser. The numerical results reveal that our theoretical result is in good agreement with experimental result in literature. Optimal active ion concentrations are proposed for the system to emit red, blue and green lights which are mixed to generate white light for display and lighting system.

Theoretical Model of Yb$^{3 + }$-Er$^{3 + }$-Tm$^{3 + }$-Codoped System for White Light Generation

We present a theoretical model of Yb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> -Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> -Tm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> -co-doped system for white light generation. The energy level, electron transition process and numerical model are proposed to calculate fluorescence intensity of the system pumped by 980 nm laser. The numerical results reveal that our theoretical model is in good agreement with experimental results in literature. Optimal active ion concentrations are proposed to enable the system to emit red, blue and green lights which are mixed to generate white light in telluride matrix for display and lighting system.

Modeling and gain properties of Er^3+ and Pr^3+ codoped fiber amplifier for 13 and 15 μm windows

A detailed analysis is presented of the possibility of an Er3+ and Pr3+ codoped fiber as an amplifier for 1.3 and 1.5 μm transmission windows. The numerical models with 1010/1480 nm and 986/1480 nm pump lasers are proposed, the rate and power propagation equations are solved numerically, and the dependence of the gains at 1310, 1530, and 1600 nm windows on pump wavelength and power, active ion concentrations, and signal wavelength are calculated. The results show that with 1010/1480 nm pumps of 200/100 mW and with fixed Pr3+ and Er3+ concentrations at 8.0×1024 and 2.0×1024 ions/m3, the signals at 1310 and 1530 nm windows may be equally amplified with a gain of 26.0 dB in the active fiber with a length of 7.0 m, and with a 1480/986 nm pump power of 100/300 mW and Pr3+ and Er3+ ion concentrations of 2.0×1024 and 2.0×1024 ions/m3, the signals at 1310 and 1530 nm may be nearly equally amplified with a gain of 8.0 dB in a 10.0 m long active fiber.

Numerical model of an Er^3+-Tm^3+-Pr^3+-codoped fiber amplifier pumped with an 800 nm laser diode

We present a numerical model of an Er3+-Tm3+-Pr3+ codoped fiber amplifier pumped with an 800 nm laser for the first time to the best of our knowledge. The rate and power propagation equations are solved numerically, and the dependence of the gains at 1310, 1470, and 1530 nm windows on the active ion concentrations and fiber length are calculated. The results show that with pump power of 20 mW, when Pr(3+)-Tm(3+)-Er(3+) concentrations are around 2.0 x 10(24), 2.0 x 10(24), and 2.26 x 10(24) (ions/m3), respectively, the signals at 1310, 1470, and 1530 nm windows may be equally amplified in the active fiber with a length of 1.3 m.

Ultra-broadband amplification properties of Ni^2+-doped glass-ceramics amplifiers

The energy level, transition configuration and mathematical model of Ni(2+)-doped glass-ceramics amplifiers are presented for the first time, to the best of one's knowledge. A quasi-three-level system is employed to model the gain and noise characteristics of the doped system, and the rate and power propagation equations of the mathematical model are solved to analyze the effect of the active ion concentration, fiber length, pump power as well as thermal-quenching on the gain spectra. It is shown that our model is in agreement with experimental result, and when excited at longer wavelength, the center of gain spectra of the amplifier red shifts, the ultra-broad band room-temperature gain spectra can cover 1.25-1.65 microm range for amplification of signal in the low-loss windows of the all-wave fiber without absorption peak caused by OH group.

Gain characteristics of 980 nm-pumped Er3+–Tm3+–Pr3+-co-doped fiber

We present a numerical model of Er3+–Tm3+–Pr3+-co-doped fiber amplifier pumped with 980 nm laser for the first time, to the best of our knowledge. The rate and power propagation equations are solved numerically to analyze the effects of the pump power and active ion concentrations on the gains at 1310, 1470, 1530, 1600, 1650 nm windows. The results show that with pump power of 200 mW and when Pr3+, Tm3+, Er3+ concentrations are around 2.0×1024, 3.0×1024, 1.5×1024 (ions/m3), respectively, the signals at 1470, 1530, 1600 nm may be nearly equally amplified with gain of 11–12.0 dB in the active fiber with length of 11.0 m, and the signals at 1310, 1470 and 1600 nm windows may be nearly equally amplified with gain of 12.0 dB in the active gain medium with length of 15.0 m. With pump power of 300 mW, the signals at 1470, 1530, 1600 nm may be nearly equally amplified with a gain of 16.0 dB in the active medium with a length of 15.0 m.

Blue-green upconversion emission in ZrO2:Yb3+ nanocrystals

Strong blue-green cooperative upconversion emission was observed under infrared excitation in 70 nm average crystallite size ZrO2:Yb3+ nanocrystals prepared by sol-gel process. The structural characterization was performed by x-ray diffraction and high resolution transmission electron microscopy suggesting that crystalline phase of nanoparticles is controlled by active ion concentration. The cooperative absorption coefficient η∼2.5×10−22 is four orders of magnitude larger than the ones reported from bulk crystals. The highest emission intensity was obtained from the doped sample at 4 mol % and was the result of the simultaneous relaxation of two excited Yb ions. Decay time of the upconverted signal τCUC≈0.310 ms is half from the near infrared effective decay time confirming the cooperative process among Yb ions. Such strong cooperative effect is explained in terms of interaction enhancement due to the diminishing of Yb–Yb separation promoted partly by the surface recombination of nanocrystals.

Optimizing the Yb:YAG thin disc laser design parameters

Based on quasi-three-level system, a numerical model of continuous wave thin disc laser is proposed. The fluorescence concentration quenching (FCQ), refractive index depending concentration effects and temperature distribution in the gain medium have been taken into account in the model. The first and second phenomena are not included in previously models. The model is used to determine optimum design parameters and to calculate the influence of various parameters like temperature, number of pump beam passes, active ions concentration and the crystal thickness on the operational efficiency of the laser. This model shows that for higher doping concentrations (>15%) the optical efficiency is decreased due to fluorescence concentration quenching. Our results are excellently in agreement with experimental results.

Optimization of Broadband Gain Spectra of Cr$^{\hbox{4}+}$:YAG Crystal Fiber Amplifier

In this paper, we present energy level, transition configuration, and numerical model of Cr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> /Cr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> :YAG crystal fiber amplifier for the first time, to the best of our knowledge. The rate and power propagation equations of the numerical model are solved and analyzed. The active ion concentration, length of the doped fiber, and pump power are optimized to maximize the bandwidth of the gain spectra. The effect of temperature on the gain spectra is also discussed. It is shown that based on analysis of the absorption spectra and emission spectra, Cr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> :YAG crystal is a three-level system, and the broadband gain of Cr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> /Cr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> :YAG crystal fiber is attributed to the broad emission of Cr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> ions, especially tetrahedral Cr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> in YAG. When excited at 800 nm, optimal fibers have ultrabroad gain spectra in the range of 1.2-1.65 mum, which cover the low-loss windows of the all-wave fiber without absorption peak caused by OH <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> group.

Dendritic properties of turtle pyramidal neurons.

The six-layered mammalian neocortex evolved from the three-layered paleocortex, which is retained in present-day reptiles such as the turtle. Thus the turtle offers an opportunity to examine which cellular and circuit properties are fundamental to cortical function. We characterized the dendritic properties of pyramidal neurons in different cortical regions of mature turtles, Pseudemys scripta elegans, using whole cell recordings and calcium imaging from the axon, soma, and dendrites in a slice preparation. The firing properties, in response to intrasomatic depolarization, resembled those previously recorded with sharp electrodes in this preparation. Somatic spikes led to active backpropagating high-amplitude dendritic action potentials and intracellular calcium ion concentration ([Ca2+]i) changes at all dendritic locations, suggesting that both backpropagation and dendritic voltage-gated Ca2+ channels are primitive traits. We found no indication that Ca2+ spikes could be evoked in the dendrites, but fast Na+ spikes could be initiated there following intradendritic stimulation. Several lines of evidence indicate that fast, smaller-amplitude somatic spikes ("prepotentials") that are easily recorded in this preparation are generated in the axon. Most synaptically activated [Ca2+]i changes resulted from Ca2+ entry through voltage-gated channels. In some cells synaptic stimulation evoked a delayed Ca2+ wave due to release from internal stores following activation of metabotropic glutamate receptors. With some small differences these properties resemble those of pyramidal neurons in mammalian species. We conclude that spike backpropagation, dendritic Ca2+ channels, and synaptically activated Ca2+ release are primitive and conserved features of cortical pyramidal cells, and therefore likely fundamental to cortical function.