Preparation and upconversion luminescence of Y2SiO5:Yb3+, Ho3+ nanophosphors

X1 type monoclinic Y2SiO5:Yb3+, Ho3+ nanophosphors with fixed (varied) Ho3+ and varied (fixed) Yb3+ concentrations were synthesized by sol-gel method. The nanophosphors presented lacunaris shape with an average size of about 47 nm measured by transmission electron microscopy and scanning electron microscopy. Up-conversion emissions have been observed at 550 nm corresponding to (5F4, 5S2)-5I8 transition and 661 nm due to 5F5-5I8 transition of Ho3+ upon 980 nm excitation at room temperature. The results indicate that both green and red luminescences are based on the two-photon process through the energy transfer from Yb3+. However, the intensity of green emission is weaker than that of the red, because the 5I7 level of Ho3+ can be effectively populated. The integrated upconversion emission intensity on the Yb3+ and Ho3+ concentrations were also studied.     

Passive mode-locking of diode-pumped Nd:GdVO4 laser with carbon nanotube intracavity absorber

By using single-walled carbon nanotubes as the saturable absorber fabricated by a vertical evaporation method, passive mode-locking of a Nd:GdVO₄ laser was realized in a W-type folded cavity. The laser generated 8?ps pulses at a repetition rate of 81?MHz. At 10.4?W of the incident pump power, average output power of 1.22?W was achieved and the corresponding peak power and energy of a single pulse were 1.88?kW and 15?nJ, respectively.     

Passively Q-switched Yb3+:YCa4O(BO3)3 laser with InGaAs quantum wells as saturable absorbers

A diode-pumped Yb:YCOB laser at 1086 nm is passively Q switched by using InGaAs quantum wells as saturable absorbers and utilizing the Bragg mirror structure as an output coupler. With an absorbed pump power of 9.2 W the laser produces pulses of 100 ms duration with average pulse energy of as much as 165 microJ at a pulse repetition rate of 7 kHz.     

Tri-wavelength passively Q-switched Yb3+:GdAl3(BO3)4 solid-state laser based on WS2 saturable absorber

Using the WS₂ nanosheets prepared by a facile hydrothermal reaction as saturable absorber (SA), we demonstrate a tri-wavelength passively Q-switching operation of a diode-pumped Yb:GdAl₃(BO₃)₄ (Yb:GAB) crystal laser for the first time. The single pulse energy up to 1.30 μJ with the output power of 140 mW is obtained. The corresponding pulse width and repetition frequency rate are 440 ns and 107.8 kHz, respectively. The stable pulsed laser operates at 1044.9, 1045.6 and 1048.5 nm, simultaneously. This work suggests that solvothermal synthesized WS₂ could be a promising SA to realize a simultaneously multi-wavelength laser operation.     

Er3+单掺与Er3+/Yb3+共掺Y2SiO5的上转换发光

报道了一种新的上转换发光材料X2型Y2SiO5:Er, Yb并研究了Yb3 浓度和泵浦功率对样品的上转换发光特性的影响:(1)随着Yb3 浓度的增加,绿、红光发射均呈先增强后减弱的变化,但相对于绿光发射,红光发射受Yb3 浓度的影响更剧烈,并且当12%(摩尔分数)Yb3 时,可以得到很纯的红光发射;(2)上转换发光强度与泵浦功率的关系表明,双光子吸收贡献样品的上转换发射.此外,讨论了可能的上转换机制.认为随着Yb3 浓度增加,Er3 的激发态吸收、Yb3 到Er3 的能量传递和Er3 的交叉弛豫对上转换发光的作用依次逐渐加强.     

Photosensitized hydrogen evolution from water using a single-walled carbon nanotube/fullerodendron/SiO2 coaxial nanohybrid

A coaxial nanohybrid consisting of a single-walled carbon nanotube (SWCNT), fullerodendron, and SiO(2) shows high-efficiency light-driven hydrogen evolution from water. Upon visible light irradiation, SWCNT/fullerodendron/SiO(2) coaxial nanohybrid shows hydrogen evolution activity in the presence of methyl viologen (MV(2+)), benzyldihydronicotinamide (BNAH), and a colloidal polyvinyl alcohol(PVA)-Pt.     

Critical oxide thickness for efficient single-walled carbon nanotube growth on silicon using thin SiO2 diffusion barriers

The ability to integrate carbon nanotubes, especially single-walled carbon nanotubes, seamlessly onto silicon would expand their range of applications considerably. Though direct integration using chemical vapor deposition is the simplest method, the growth of single-walled carbon nanotubes on bare silicon and on ultrathin oxides is greatly inhibited due to the formation of a noncatalytic silicide. Using X-ray photoelectron spectroscopy, we show that silicide formation occurs on ultrathin oxides due to thermally activated metal diffusion through the oxide. Silicides affect the growth of single-walled nanotubes more than multi-walled nanotubes due to the increased kinetics at the higher single-walled nanotube growth temperature. We demonstrate that nickel and iron catalysts, when deposited on clean silicon or ultrathin silicon dioxide layers, begin to form silicides at relatively low temperatures, and that by 900 degrees C, all of the catalyst has been incorporated into the silicide, rendering it inactive for subsequent single-walled nanotube growth. We further show that a 4-nm silicon dioxide layer is the minimum diffusion barrier thickness that allows for efficient single-walled nanotube growth.     

Luminescence enhancement of Tb3+ in Sr3SiO5:Eu2+ phosphor

Sr₃SiO₅ phosphors co-doped with Eu²⁺ and Tb³⁺ were prepared by a conventional solid-state reaction method. The prepared Sr₃SiO₅:Eu²⁺,Tb³⁺,Li⁺ phosphors had characteristic luminescent spectra excited under near-UV excitation in which both the broadband spectrum assigned to Eu²⁺ and the line spectrum assigned to Tb³⁺ are observed, although Tb³⁺ is inactive with this photon energy in general. For Eu²⁺–Tb³⁺ codoped Sr₃SiO₅, energy transfer process takes place and the mechanism is ascribed to the overlap between the shorter Eu²⁺ luminescence band from the Sr₃SiO₅ crystal structure with two Sr sites and ₅D⁴ energy level of Tb³⁺ ion. Due to the energy transfer, PL intensity of Eu²⁺ emission increased about 26 %. We suggest that this enhancement mechanism could shed light on the potential applications in white light-emitting diodes excited by near-UV light. In addition, the emission peak position near the orange region indicates that our system is a step towards a new class of wavelength sources for artificial lighting with improved PL intensity and lower energy consumption.     

Yb3+掺杂SiO2-Bi2O3-B2O3玻璃的物理性质及光谱性质

选取玻璃组分60SiO₂-xBi₂O₃-(30-x)B₂O₃-2K₂O-7Na₂O-1Yb₂O₃(以mol％记,x=0,5,10,15,20,25,30)为研究对象。通过测试试样的物理性质和光谱性质,应用倒易法(reciprocity method)计算Yb³⁺离子的受激发射截面(σ_emi),并且计算了Yb³⁺的自发辐射几率(A_rad),²F_5/2能级的辐射寿命(T_rad)。讨论了玻璃中Bi₂O₃和B₂O₃的组成变化对其物理性质、Yb³⁺离子的吸收特性、发光特性以及OH^-离子对实测Yb³⁺荧光寿命(T_f)的影响。结果表明:Yb³⁺掺杂的Si₂-Bi₂O₃-B₂O₃具有较好的光谱性能,是一种新型的Yb³⁺掺杂双包层光纤候选基质材料。     

Site-selective hole burning in Eu3+:Y2SiO5

We found that the Eu(3+) ion occupies several distinct sites in Y(2)SiO(5). We were also able to perform hole-burning studies in more than 40 different transitions.     

Passively Q-switched mode-locking Nd:GdVO4 laser with a chemically reduced graphene oxide saturable absorber

A diode-pumped passively Q-switched mode-locking Nd:GdVO₄ laser using a chemically reduced graphene oxide saturable absorber was demonstrated. The repetition rate and pulse width of the Q-switching envelopes were 5.7 MHz and 100 ns, respectively, while those of the mode-locking pulses that were modulated in the Q-switching envelopes were 139 MHz and 10 ps. At the maximum pump power of 7 W, the average output power was 1.38 W, corresponding to a slope efficiency of 25%.     

Numerical study of passive Q switching of a tunable alexandrite laser with a Cr:Y2SiO5 solid-state saturable absorber

Passive Q switching of a tunable alexandrite solid-state laser with a Cr:Y(2)SiO(5) solid-state saturable absorber is numerically studied over a major portion of the alexandrite tuning range. The theory of passive Q switching with a slowly relaxing saturable absorber is studied and utilized for evaluating the performance of the Cr:YSO Q-switched alexandrite laser system. With a typical laser configuration, a Q-switched laser pulse of 262 mJ in 23 ns is obtained.     

Decoration of carbon nanotube with SiO2 nanoparticles to improve polyelectrolyte membrane performance

To overcome the poor mechanical performance and the low proton conductivity at high temperature (> 80 degrees C) which hinder the utilization of Nafion membranes for use in PEM Fuel Cell, SiO2 nanoparticle decorated multi-walled carbon nanotubes (MWCNTs) were developed to reinforce both the mechanical property and the water retention capability of Nafion membranes. Results show that the composite membrane is approximately 10% and 5-10% higher than that of recast Nafion membrane in proton conductivity and water retention, respectively. These could be explained by the bifunction of SiO2 which performs both hydrophilicity and proton conductivity. In addition, the mechanical performance was greatly enhanced in the presence of SiO2 decorated MWCNTs.     

Diode-pumped passively mode-locked Nd:YAG laser at 1338 nm with a semiconductor saturable absorber mirror

We demonstrate a diode-end-pumped passively mode-locked 1338 nm Nd:YAG laser with a semiconductor saturable absorber mirror. At the absorbed pump power of 8.89 W, an average output power of 1.12 W was obtained with a slope efficiency of 14%. The pulse width was 22.4 ps with a repetition rate of 63.9 MHz, corresponding to a peak power of 782 W. In addition, the bandwidth of the mode-locking spectrum is as narrow as 20.44 GHz, which shows the potential application in long-distance ranging and fiber information transmission because of the low dispersion of these ultrashort pulses.     

Laser-diode pumped passively Q-switched Nd3+:NaY(WO4)2 laser with Cr4+:YAG saturable absorber

A laser-diode pumped passively Q-switched new type crystal Nd³⁺:NaY(WO₄)₂ (known as Nd:NYW) laser with Cr⁴⁺:YAG saturable absorber has been realized. The dependence of pulse repetition rate, pulse energy, pulse width, and peak power on pump power for different small-signal transmission of Cr⁴⁺:YAG are measured. The coupled rate equations are used to simulate the Q-switched process of laser, and the numerical solutions agree with the experimental results.     

Yb3+ concentration dependence of upconversion luminescence in Y2Sn2O7:Yb3+/Er3+ nanophosphors

Pyrochlore Y₂Sn₂O₇ nanophosphors codoped with Er³⁺ (fixed 2 at.%) and Yb³⁺ ions (2–16 at.%) were synthesized via hydrothermal process followed by heat treatment. We investigate the infrared-to-visible upconversion (UC) luminescence properties of Er–Yb codoped Y₂Sn₂O₇. Upon 980 nm excitation at room temperature, green (at ~522 and 544 nm) and red (at ~661 nm) UC emissions were observed, which are ascribed to the (²H_11/2, ⁴S_3/2) → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions, respectively. It has been found that the Yb³⁺-doping concentrations have greatly influenced on the UC luminescence intensity and the emission ratio of the red and green in Y₂Sn₂O₇:Yb³⁺/Er³⁺ nanophosphors. The tunable emission is due to the energy back transfer from Er³⁺ to Yb³⁺ and the cross relaxation between the two neighboring Er³⁺ ions. It is expected that the achieved single and intense red emission band may have potential application for in vivo bioimaging.     

Passively Q-switched Nd:YVO(4) laser with a Cr(4+):YAG crystal saturable absorber

We demonstrate, for the first time as far as we know, a passively Q-switched operation of a Nd:YVO(4) laser in which a Cr(4+):YAG crystal and a laser-diode bar are used as the saturable absorber and the pump source, respectively. Stable laser pulses as short as 28 ns with 20-muJ energy can be generated with this laser, which has the advantages of simplicity, high efficiency, and good long-term stability.     

Optical spectroscopy of a La3Ga5SiO14:Co2+ crystal

The absorption, luminescence, and circular dichroism spectra of a cobalt-doped La₃Ga₅SiO₁₄ crystal (Ca₃Ga₂Ge₄O₁₄ structure, sp. gr. P321) have been studied in the range 8–300 K. The Co²⁺ ion has been shown to occupy the 3f tetrahedral site. For T < 220 K, the ² E(² G) → ⁴ A ₂ and ⁴ T ₁(⁴ P) → ⁴ A ₂ transitions of the tetrahedrally coordinated Co²⁺ ion are active in the luminescence spectrum. For T > 220 K, the ² E(² G) state is completely quenched, and only luminescence from the ⁴ T ₁(⁴ P) level is observed.     

Photoluminescence mapping of "as-grown" single-walled carbon nanotubes: a comparison with micelle-encapsulated nanotube solutions

Band gap photoluminescence (PL) is observed from "as-grown" single-walled carbon nanotubes (SWNTs) in solid form. The relative PL intensities for six specific semiconducting SWNTs are compared directly to those of the micelle-encapsulated SWNTs' solutions to investigate the influence of the micelle dispersion process on PL measurements. The results indicate that sodium dodecyl sulfate (SDS) and sodium cholate (SC) selectively solubilize smaller-diameter nanotubes, whereas sodium dodecylbenzene sulfonate (SDBS) solution does not exhibit significant diameter selectivity within the diameter range studied here (d(t) = 0.829-0.966 nm).