Crystal growth and spectral properties of Tb:Lu_2O_3

The crystal growth,x-ray diffraction pattern,absorption spectrum,emission spectrum,and fluorescence lifetime of a Tb:Lu_2O_3 single crystal were studied.Excited at 483 nm,the peak absorption cross-section was calculated to be 3.5×10~(-22)cm~2,and the full width at half maximum was found to be 2.85 nm.The Judd-Ofelt(J-O)intensity parameters ?_2,?_4,and ?_6 were computed to be 3.79×10~(-20)cm~2,1.30×10~(-20)cm~2,and 1.08×10~(-20)cm~2,with a spectroscopic quality factor ?_4/?_6 being 1.20.The emission cross-sections of green emission around 543 nm and yellow emission around 584 nm were calculated to be 9.43×10~(-22)cm~2 and 1.32×10~(-22)cm~2,respectively.The fluorescence lifetimeτexp of ~5D_4 was fitted to be 1.13 ms.The data suggest that the Tb:Lu_2O_3 crystal could be a potential candidate for green and yellow laser operation.     

Spectroscopic and laser properties of Er~(3+), Pr~(3+) co-doped LiYF_4 crystal

In this paper, the absorption and fluorescence spectra of Er~(3+), Pr~(3+)co-doped LiYF_4(Er,Pr:YLF) crystal were measured and analyzed. The Pr~(3+)co-doping was proved to effectively enhance the Er~(3+)∶~4I_(11/2)→~4I_(13/2) mid-infrared transition at the 2.7 μm with 74.1% energy transfer efficiency from Er~(3+)∶~4I_(13/2) to Pr~(3+)∶~3F_4. By using the Judd–Ofelt theory, the stimulated emission cross section was calculated to be 1.834 × 10~(-20) cm~2 at 2685 nm and 1.359 × 10~(-20) cm~2 at 2804.6 nm.Moreover, a diode-end-pumped Er,Pr:YLF laser operating at 2659 nm was realized for the first time, to the best of our knowledge. The maximum output power was determined to be 258 m W with a slope efficiency of 7.4%, and the corresponding beam quality factors M~2_x= 1.29 and M~2_y= 1.25. Our results suggest that Er,Pr:YLF should be a promising material for 2.7 μm laser generation.     

Investigation of the growth and optical properties of a Co~(2+)-doped Na_5Lu_9F_(32) single crystal

A 0.1 mol.% CoF_2-doped Na_5Lu_9F_(32)single crystal with high quality in the size of ～φ10 mm×100 mm was grown by the Bridgman method. Three peaks located at 504, 544, and 688 nm and a broad band in the range of 1200–1600 nm centered at 1472 nm were observed in the absorption spectra. The absorption peak position suggests cobalt ions in the divalent state in the grown crystal. Moreover, the cobalt ions are confirmed to locate in the distorted cubic crystal structure. Upon excitation of 500 nm light, a sharp emission peak at 747 nm ascribed to the ~2T_2(H_1) →~4A_2(F) transition was observed for the crystal. The Co~(2+)-doped Na_5Lu_9F_(32)crystal shows a potentially promising material for the application of a passively Q-switched laser operating in the near-infrared range.     

Crystal growth,spectral properties and Judd–Ofelt analysis of Pr: CaF_2-YF_3

The 0.6 at.% Pr~(3+)-doped CaF_2-YF_3 crystal was successfully grown by the temperature gradient technique(TGT).X-ray diffraction analysis showed that the grown crystal still had cubic structure. The absorption spectrum, emission spectrum, Judd–Ofelt analysis and fluorescence decay curve at room temperature were discussed. The fluorescence lifetime of Pr: CaF_2-YF_3 crystal was 45.46 μs, and the σem ·τ of ~3P_0→~3H_6 and ~3P_0→~3F_2 transitions were calculated to be 80.92 × 10~(-20) cm~2·μs and 388.7 × 10~(-20) cm~2·μs, respectively. The FWHMs are 20.1 nm and 6.8 nm, which are higher than those of Pr: LiYF_4, Pr:LiLuF_4, Pr: LiGdF_4 and Pr: BaY_2F_8 crystals. The results show that the Pr: CaF_2-YF_3 crystal is expected to achieve 605 nm orange light and 642 nm red light laser operation.     

Crystal Structure and Judd–Ofelt Analysis of Er~(3+) Doped LuAl_3(BO_3)_4 Crystal

Single crystal Er:LuAl_3(BO_3)(Er:Lu AB) is successfully grown using the top-seeded solution growth method with a K_2Mo_3O_(10) flux. The cell parameters of the grown crystal are estimated by an x-ray single crystal diffactometor and x-ray powder diffraction analysis. The result indicates that it still belongs to the space group R32. The obtained unit-cell parameters are a= 9.2793(19) ?, c= 7.210(3) ?, V= 537.65(27) ?~3, and Z=3.The absorption spectrum is measured at room temperature. The spectroscopy properties are investigated based on the Judd–Ofelt(J-O) theory, and the effective J-O parameters were calculated to be Ω_2=8.33×10~(-20),Ω_4=3.83×10~(-20), and Ω_6 =3.55×10~(-20). The emission spectra of Er:LuAB crystal at room temperature are also studied and the ~4I_(11/2)→~4I_(13/2) fluorescence around 3170 nm is observed. The emission cross section calculated by the F-L formula is 8.6×10~(-20) cm~2. These results suggest that the Er:LuAB crystal may be a promising ~3 μm laser material.     

Mechanisms and absolute quantum yield of upconversion luminescence of fluoride phosphors

Mechanisms of upconversion luminescence(UCL) of SrF_2:Er phosphors corresponding to the ~4G_(11∕2)→~4I_(15∕2),~2H_(9∕2)→~4I_(15∕2),~4F_(5∕2)→~4I_(15∕2),~4F_(7∕2)→~4I_(15∕2),~2H_(11∕2)→~4I_(15∕2),~4S_(3∕2)→~4I_(15∕2),~4F_(9∕2)→~4I_(15∕2), and ~4I_(9∕2)→~4I_(15∕2) transitions upon excitation of the ~4I_(11∕2) level of Er~(3+)ions were investigated. Energy transfer upconversion processes are responsible for the populating of the ~2H_(9∕2),~2H_(11∕2),~4S_(3∕2), and ~4F_(9∕2) levels. Cooperative process is the dominant mechanism of luminescence from ~4S_(3∕2) and ~4F_(9∕2) levels for SrF_2:Er with high concentrations of Er~(3+)ions. The UCL from ~4G_(11∕2) and ~4F_(5∕2) is explained by excited-state absorption. Cross-relaxation processes take part in the population of ~4F_(9∕2) and ~4I_(9∕2) levels. For quantifying material performance, the Er~(3+)-concentration dependence of UCL and the absolute quantum yields of SrF_2:Er were studied. The most intensive visible luminescence was obtained for SrF_2:Er(14.2%) with 0.28% maximum quantum yield.     

Experimental study of cesium 5D 5D→6S (nL=9D,11S,7F)energy pooling collisions

We report experimentally the measured rate coefficients for the energy pooling(EP)collisions process Cs(5D) Cs(5D)→Cs(6S) Cs(nL=9D,11S,7F)in cesium densities of 10~(16)-10~(17)cm~(-3).The 5D state was populated via 8S→7P→5D spontaneous emission following two-step pumping 6S→6P_(3/2)→8S. Since the 5D→6P(3.0—3.6μm)fluorescence could not be detected in this experiment,we carried out a relative measurement for the process 6P 5D→6S 7D.The excited-atom density and spatial distribution were mapped by monitoring the absorption of a counterpropagating single-mode laser beam, tuned to 6P_(3/2)→9S_(1/2)transition,which could be translated parallelly to the pump beam.The excited atom densities have been combined with the measured fluorescence ratios to yield EP rate coefficients. The average values for nL=9D,11S and 7F are 8.0±4.0,7.0±3.5,and 9.3±4.6(in units of 10~(-10) cm~3/s),respectively.Influence of the energy transfer process 11S 6S(?)7F 6S on the rate coefficients k_(11S)and k_(7F)is also discussed.     

Description of mixed symmetry states in ~(96)Ru using IBM-2

We have investigated the properties of low-lying states in ~(96)Ru within the framework of the neutron-proton interacting boson model(IBM-2), with special attention paid to the characteristics of the mixed symmetry states. By considering the relative energy of d proton boson to be different from that of neutron boson, the level energies and M1, E2 transition strengths have been calculated. The IBM-2 calculation is consistent with the experimental data of ~(96)Ru both quantitatively and qualitatively.Particularly, the strong M1 transition between the 4_2~+ and 4_1~+ states has been reproduced nicely. The calculated results show that the M1 transition strength of B(M1, 4_2~+→ 4_1+) in ~(96)Ru can be described successfully by the IBM-2.     

Investigation of low-temperature cathodoluminescence mechanism of Er-doped Ga N thick films by ion implantation

Er ions are implanted into the Ga N thick films grown by hydride vapor phase epitaxy. The implantation energy is 200 ke V and the implantation doses are 1×10~(13),1 × 10~(14),1 × 10~(15),and 5×10~(15) atom∕cm~2,respectively. The effects of the implantation dose and annealing temperature on the Ga N band-edge luminescence are investigated. The cathodoluminescence spectra from 82 to 323 K are measured for 1×10~(15) atom∕cm~2-implanted Ga N annealed at 1100°C. Luminescence peaks at 356,362,376,390,and 414 nm are observed on the 82 K cathodoluminescence spectrum. When the temperature is increased to 150 K,the intensities of the 356 and 414 nm peaks are nearly unchanged and the 362,376,and 390 nm peaks disappear. The intensity ratio of 538 nm(~2H_(11∕2)→ ~4I/_(15∕2)) and 559 nm(~4S_(3∕2)→ ~4I_(15∕2)) is increased with the increase in temperature. We try to shed light on the above interesting phenomena.     

Er~(3+)掺杂Na_5Lu_9F_(32)单晶体的红外光学特性

采用坩埚下降法成功地生长了Er~(3+)离子掺杂的Na_5Lu_9F_(32)(NLF)单晶体。测定了单晶体在400~2 500nm波段的吸收光谱与2.5~25μm红外波段的透过光谱。Na_5Lu_9F_(32)单晶体在400~7 150 nm宽波段范围具有好的光学透过性,在该波段的透过率达到90%。在透过光谱中几乎观察不到2.7μm中红外波段的吸收,说明单晶体中OH~-离子的含量极低。根据测定的吸收光谱,通过Judd-Ofelt理论计算了Er~(3+)在单晶体中的光学强度参数Ω_t(Ω_2=2.08,Ω_4=2.07,Ω_6=0.75),以及相应的辐射跃迁速率、荧光分支比和荧光寿命。根据Futchbauer-Ladenburg公式估算了样品的发射截面大约分别为1.42×10~(-20)cm~2(~4I_(13/2)→~4I_(15/2))和1.66×10~(-20)cm~2(~4I_(11/2)→~4I_(13/2))。在980 nm半导体激光器(LD)激发下,研究了单晶体的近红外1.5μm与中红外2.7μm的发射光谱特性。     

An improved strontium lattice clock with 10~(-16) level laser frequency stabilization

A clock laser based on a 30-cm-long ultrahigh finesse optical cavity was developed to improve the frequency stability of the Sr optical lattice clock at the National Institute of Metrology. Using this clock laser to probe the spin-polarized~(87)Sr atoms, a Rabi transition linewidth of 1.8 Hz was obtained with 500 ms interrogation time.Two independent digital servos are used to alternatively lock the clock laser to the ~1S_0(m_F=+9∕2)→~3P_0(m_F=+9∕2)transition. The Allan deviation shows that the short-term frequency stability is better than3.2 × 10~(-16)and averages down followed by 1.8 × 10~(-15)∕τ~(1/2).     

Investigation of trace p-dichlorobenzene using laser mass spectrometry

The time-of-flight mass spectrum(TOFMS)relative to the resonant two-photon ionization of gas phase p- dichlorobenzene was obtained in the wavelength range of 240-250 nm by a home-made system.A special design was made to reduce the effect of memory on the inner wall of the sample inlet system suitable for the investigation of semi-volatile organic compound.In this wavelength range,p-dichlorobenzene molecules firstly absorbed one photon to be excited from the gTound state ~1A_g(S_0)to the first excited state 1B2u($1),then absorbed another photon to be ionized.The relationship between the signal intensity of p-dichlorobenzene molecular ion C_6H_4~(35)Cl_2~ at 248-nm wavelength and the laser power was given. The 1.52 power index of C_6H_4~(35)Cl_2~ was a typical identification of the 3/2 power law.The relationship between the ion signal intensity of C_6H_4~(35)Cl_2~ and the sample concentration was close to a linear one in the ppm(V/V)range,which led to a detection limit of 125 ppb(V/V)for p-dichlorobenzene.     

Electronic structure and photoluminescence property of a novel white emission phosphor Na_3MgZr(PO_4)_3:Dy~(3+) for warm white light emitting diodes

To explore suitable single-phase white emission phosphors for warm white light emitting diodes, a series of novel phosphors Na_3MgZr(PO_4)_3:xDy~(3+)(0 ≤ x ≤ 0.03) is prepared, and their phase purities as well as photoluminescence properties are discussed in depth via x-ray diffraction structure refinement and photoluminescence spectrum measurement.The electronic structure properties of the Na_3MgZr(PO_4)_3host are calculated. The results reveal that Na_3MgZr(PO_4)_3 possesses a direct band gap with a band gap value of 4.917 e V. The obtained Na_3MgZr(PO_4)_3:Dy~(3+) phosphors are all well crystallized in trigonal structure with space group Rc, which has strong absorption around 365 nm and can generate warm white light emissions peaking at 487, 576, and 673 nm upon ultraviolet excitation, which are attributed to the transitions from ~4F_(9/2) to ~6H_(15/2),~6H_(13/2), and ~6H_(11/2) of Dy~(3+) ions, respectively. The optimal doping content, critical distance, decay time, and Commission International de L'Eclairage(CIE) chromaticity coordinates are investigated in Dy~(3+) ion-doped Na_3MgZr(PO_4)_3. The thermal quenching analysis shows that Na_3MgZr(PO_4)_3:Dy~(3+) has a good thermal stability, and the thermal activation energy is calculated. The performances of Na_3MgZr(PO_4)_3:Dy~(3+) make it a potential single-phase white emission phosphor for warm white light emitting diode.     

Time-resolved spectroscopy for 5s~('4)D_(7/2) state transitions undergoing electron–ion recombination in femtosecond laser-produced copper plasma

In the femtosecond laser-produced Cu-plasma, the transient transition dynamics that the excited state 5s~('4)D_(7/2) via electron–ion recombination transfers to 4p~('4)F_(9/2)~0(465.11 nm, Λ1 line) and 4p~('4)D_(7/2)~0(529.25 nm, Λ_2 line) states are investigated by using the time-resolved spectroscopy. The occupation number and relevant lifetime of the excited state 5s~('4)D_(7/2),the temporal evolutions of spectral intensities for Λ_1 line and Λ_2 line emissions are demonstrated to be in direct proportion to the employed laser intensity, which reveals the transient features of transition dynamics clearly differing from that resulted in the traditional collision excitation. Furthermore, some unique characteristics for Λ_1 and Λ_2 transitions stemming from electron–ion recombination are examined in detail.     

Confirmation/Observation of Hindered E2 Strengths in-16,18C

The lifetime of the first excited 2~+ state in ~(18)C was measured using an upgraded recoil shadow method to determine the electric quadrupole transition.The measured mean lifetime is 18.9±0.9 (stat)±4.4 (syst) ps,which corresponds to a B(E2;2~+_1→0~+_(gs)) value of (4.3±0.2±1.0) e~2fm~4,or about 1.5 Weisskopf units.The mean lifetime of the first 2~+ state in ~(16)C was remeasured to be about 18 ps,about four times shorter than the value reported previously.This discrepancy was explained by incorporating the γ-ray angular distribution measured in this work into the previous measurement.The observed transition strengths in ~(16,18)C are hindered compared to the empirical transition strengths,indicating that the anomalous hindrance observed in ~(16)C persists in ~(18)C.     

An optimized ion trap geometry to measure quadrupole shifts of ~(171)Yb~+ clocks

We propose a new ion-trap geometry to carry out accurate measurements of the quadrupole shifts in the ~(171)Yb ion.This trap will minimize the quadrupole shift due to the harmonic component of the confining potential by an order of magnitude.This will be useful to reduce the uncertainties in the clock frequency measurements of the 6s ~2S_(1/2)→4f~(13)6s~2 ~2F_(7/2)and 6s ~2S_(1/2)→5d~2D_(3/2) transitions,from which we can deduce the precise values of the quadrupole moments(0s) of the 4f~(13)6s~2 ~2F_(7/2) and 5d~2D_(3/2) states.Moreover,it may be able to affirm the validity of the measured 0 value of the4f~(13)6s~2~2F_(7/2) state,for which three independent theoretical studies defer almost by one order of magnitude from the measurement.We also calculate 0s using the relativistic coupled-cluster(RCC) method.We use these 0 values to estimate the quadrupole shift that can be measured in our proposed ion trap experiment.     

Room-temperature operating extended short wavelength infrared photodetector based on interband transition of InAsSb/GaSb quantum well

Here in this paper,we report a room-temperature operating infrared photodetector based on the interband transition of an In As Sb/Ga Sb quantum well.The interband transition energy of 5-nm thick In As_(0.91)Sb_(0.09) embedded in the Ga Sb barrier is calculated to be 0.53 e V(2.35μm),which makes the absorption range of In As Sb cover an entire range from short-wavelength infrared to long-wavelength infrared spectrum.The fabricated photodetector exhibits a narrow response range from 2.0μm to 2.3μm with a peak around 2.1μm at 300 K.The peak responsivity is 0.4 A/W under-500-m Vapplied bias voltage,corresponding to a peak quantum efficiency of 23.8%in the case without any anti-reflection coating.At 300 K,the photodetector exhibits a dark current density of 6.05×10~(-3)A/cm~2under-400-m V applied bias voltage and3.25×10~(-5)A/cm~2under zero,separately.The peak detectivity is 6.91×10~(10)cm·Hz~(1/2)/W under zero bias voltage at 300 K.     

Intensities and spectral features of the ~4I_(13/2)-~4I_(15/2) potential laser transition of Er~(3+) centers in CaF_2-CeF_3 disordered crystal

A CaF_2-CeF_3 disordered crystal containing 1.06% of Er~(3+) ions was grown by the temperature gradient technique.Optical absorption and emission spectra recorded at room temperature and at 10 K, luminescence decay curve recorded at room temperature, and extended x-ray-absorption fine structure spectra were analyzed with an intention to assess the laser potential related to the ~4I_(13/2)→~4I_(15/2) transition of Er~(3+). In addition, the thermal diffusivity of the crystal was measured at room temperature. The analysis of room-temperature spectra revealed that the ~4I_(13/2) emission is long-lived with a radiative lifetime value of 5.5 ms, peak emission cross section of 0.73 × 10~(-20) cm~2, and large spectral width pointing at the tunability of the emission wavelength in the region stretching from approximately 1480 nm to 1630 nm. The energies of the crystal field components for the ground and excited multiplets determined from low-temperature absorption and emission spectra made it possible to predict successfully the spectral position and shape of the room-temperature ~4I_(13/2)→~4I_(15/2) emission band. Based on the correlation of the optical spectra and dynamics of the luminescence decay, it was concluded that in contrast to Yb~(3+) ions in heavily doped CaF_2 erbium ions in the CaF_2-CeF_3 crystal reside in numerous sites with dissimilar relaxation rates.     

GSA and ESA dual-wavelength pumped 2.3 μm Tm:YLF laser on the ~3H_4→~3H_5 transition

The population trapping effect of the ~3F_4 level is an important factor limiting the power scaling of the 2.3 μm thulium(Tm)laser on the ~3H_4→~3 H_5 transition.In this Letter,we demonstrate a novel scheme of ground state absorption(GSA)(~3 H_6→~3H_4) and excited state absorption(ESA)(~3F_4→~3H_4] dual-wavelength pumped 2.3 μm Tm lasers.Introducing an ESA pumping process can accurately excite the Tm~(3+) ions accumulated in the ~3F_4 level to the ~3H_4 level,constructing a double populating mechanism for the upper laser level ~3H_4.A proof-of-principle experimental demonstration of the GSA(785 nm) and ESA(1470 nm) dual-wavelength pumped 2.3 μm Tm:LiYF_4(Tm:YLF) laser was realized.A maximum continuous-wave output power of 1.84 W at 2308 nm was achieved under 785 and 1470 nm dual-wavelength pumping,increased by60% compared with the case of 785 nm single-wavelength pumping under the same resonator condition.Our work provides an efficient way to achieve higher output power from 2.3 μm Tm-doped lasers on the ~3H_4→~3 H_5 transition.     

Spectroscopic properties of Er~(3+)-doped AlF_3-La_2O_3-Al_2O_3-SiO_2 glasses

Er~(3+)-doped fluoride lanthanum aluminosilicate glasses with compositions of (65-x/2)SiO_2·(25-x/2)Al_2O_3·xAlF_3·9.1La_2O_3·0.6Er_2O_3·0.3Yb_2O_3(x=4, 8, 12, 20, 30) (mol%) were prepared and their glass transition temperatures and spectroscopic properties were investigated.The Ω_2, Ω_4, and Ω_6 intensity parameters of glasses were calculated by Judd-Ofelt theory from absorption curves. It was found that glasses transition temperature and melting temperature decreased with the increase of fluoride content in glass,Ω_2 decreased gradually with the increase of AlF_3 content,but both Ω_4 and Ω_6 did not increase until AlF_3 content increased to 30 mol%.The quantum efficiency of ~4I_(13/2) to ~4I_(15/2) transition of Er~(3+) ions increases with the increase of AlF_3 content in glass.Fluorescent lifetime is longer in glass containing more AlF_3 content.