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A series of high quality x%Pr3+:BaF2 (x = 0.6, 1, 2); (1%Pr3+, 2%Na+):BaF2; (1%Pr3+, y%Ca2+):BaF2 (y = 3, 5) and (0.6%Pr3+, 10%R3+):BaF2 (R = Y, Lu, Gd) crystals were grown by temperature gradient technique (TGT). The Raman spectra, absorption spectra, fluorescence spectra, and fluorescence decay lifetime were measured. XRD patterns indicate that the as-synthesized samples are pure BaF2 phase. The absorption cross-section of Pr3+ ions in the BaF2 matrix can be greatly improved by co-doping R3+ ions, while improvement by Na+ and Ca2+ ions is marginal. The fluorescence characteristic of Pr3+ ions can be effectively regulated by co-doping Na+, Ca2+, R3+ (R = Y, Lu, Gd) ions of different valence states. When R3+ ions are introduced, the fluorescence spectra show the strongest orange emission and the CIE chromaticity coordinates of Pr3+ ions are also in the orange region. When single-doped Pr3+ ions and Na+ or Ca2+ ions are introduced, the fluorescence lifetime of the 3P0 level is double exponential decay, and the short lifetime is the main proportion. However, the fluorescence centers tend to homogeneous and stable by R3+ ions co-doping and the fluorescence lifetime exhibits single-exponential decay, which is fitted to 49.7 μs, 47.8 μs and 49.6 μs of (0.6%Pr3+, 10%R3+):BaF2 (R = Y, Lu, Gd), respectively. All the results show that (Pr3+, Gd3+):BaF2 and (Pr3+, Na+):BaF2 are excellent laser gain media for high-efficiency orange and red laser operation. [ABSTRACT FROM AUTHOR]

Highlights: [•] Spectroscopic properties and crystal growth of Tm:LYSO single crystal were studied for the first time. [•] The large absorption and emission cross-section and broad FWHM make Tm:LYSO a promising media for tunable and ultrashort pulses. [•] The J–O parameters and gain spectra reveal that the excellent properties for laser applications. [Copyright &y& Elsevier]

Abstract: Yb3+-doped (Lu0.5Y0.5)3Al5O12 (Yb:LuYAG) single crystal has been grown by the Czochralski method. The segregation coefficient of Yb3+ was studied by the inductively coupled plasma atomic emission spectrometry (ICP-AES) method. The crystal structure has been determined by X-ray diffraction analysis. The absorption and emission spectra and fluorescence lifetime of Yb:LuYAG crystal were measured at room temperature. The spectroscopic parameters of Yb:LuYAG crystal were compared with those of Yb:YAG and Yb:LuAG crystals with the same doping level. The results indicate that Yb:LuYAG crystals are potential candidates for high-power ultrashort pulse lasers. [ABSTRACT FROM AUTHOR]

Abstract: A Yb3+-doped CaYAlO4 laser crystal has been grown by the Czochralski technique. The segregation coefficient was measured by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). The cell parameters were analyzed with X-ray diffraction experiments. Color defects in Yb:CaYAlO4 have been evidenced to be similar to those in undoped CaYAlO4. The polarized absorption spectra and the fluorescence spectrum of the Yb:CaYAlO4 crystal were measured at room temperature. The fluorescence decay time of the Yb3+ ion was investigated. The results show that Yb:CaYAlO4 has potential as a laser gain medium for an ultrashort laser system. [Copyright &y& Elsevier]

Abstract: We review the investigation of a single quantum dot driven by a strong optical field. By coherent pump-probe spectroscopy, we demonstrate the Autler–Townes splitting and Mollow absorption spectrum in a single neutral quantum dot. Furthermore, we also show the typical Mollow absorption spectrum by driving a singly charged quantum dot in a strong optical coupling regime. Our results show all the typical features of an isolated atomic system driven by a strong optical field, such as the AC stark effect, Rabi side bands and optical gain effect, which indicate that both neutral and charged quantum dots maintain the discrete energy level states even at high optical field strengths. [Copyright &y& Elsevier]

Abstract: The effects of gamma-irradiation on the air-annealed 10at.% Yb:Y3Al5O12 (YAG) and air annealing on the gamma-irradiated 10at.% Yb:YAG have been studied by the difference absorption spectra before and after treatment. The gamma-irradiation and air annealing led to opposite changes of the absorption properties of the Yb:YAG crystal. After air annealing, the gamma-irradiation induced centers were totally removed and the concentration of Fe3+ and Yb3+ were lightly increased. For the first time, the gamma-irradiation induced valence changes between Yb3+ and Yb2+ ions in Yb:YAG crystals have been observed. [Copyright &y& Elsevier]

Two-dimensional (2D) CuO nanoplatelets were synthesized in the presence of ionic liquids under the mild hydrothermal conditions at 140°C by self-assembly. The thickness of CuO nanoplatelets was about 35 nm prepared in 1-butyl-3-methylimidazolium chloride. XRD, FESEM, and TEM were used to characterize the structure features of the products. FTIR spectra and TG curves confirmed the adsorption of ionic liquids on the surface of CuO nanoplatelets. In addition, UV-visible absorption spectra were employed to estimate the band gap energies of the CuO nanoplatelets as nanosized semiconductors. It was demonstrated that the ionic liquids could act as a cosolvent, soft template agent and modifiers. [ABSTRACT FROM AUTHOR]

Abstract: Yb:Y3Al5O12 (Yb:YAG) single crystals with Yb doping concentration 0.5at.%, 5at.%, 15at.%, 25at.%, 50at.%, 100at.% and Yb:YAlO3 (Yb:YAP) single crystals with Yb doping concentration 0.5at.%, 5at.%, 15at.%, 30at.% were grown by the Czochralski process. The fluorescence spectra of these crystals and the effects of self-absorption on the shape of the fluorescence spectra were studied. Through comparing the fluorescence spectra of Yb:YAG and Yb:YAP, all results indicate that the effects of self-absorption on the fluorescence spectra of Yb:YAP are remarkably stronger than that of Yb:YAG at the same Yb concentration. [Copyright &y& Elsevier]

Abstract: Absorption spectrum from 400 to 2000nm and upconversion fluorescence spectra under 940nm pumping of YAG single crystal codoped with 5at.% Yb3+ and 4at.% Tm3+ were studied at room temperature. The blue upconversion emission centered at 483nm corresponds to the transition 1G4 → 3H6, the emission band around 646nm corresponds to the transition 1G4 → 3F4 of Tm3+. Energy transfer from Yb3+ to Tm3+ is mainly nonradiative and the transfer efficiency was experimentally assessed. The line strengths, transition probabilities and radiative lifetimes of 1G4 level were calculated by using Judd–Ofelt theory. Gain coefficient calculated from spectra shows that the upconversion corresponding with transitions 1G4 → 3H6 in YAG doped with Yb3+ and Tm3+ is potentially useful for blue light output. [Copyright &y& Elsevier]

Abstract: Yb:YAG single crystals with Yb doping concentration 5.4, 16.3, 27.1, 53.6, and 100at.% were grown by the Czochralski process. The effects of Yb concentration on the absorption spectra (190–1100nm), fluorescence spectra under 940nm and X-ray excitation were studied. The concentration quenching of fluorescence was observed when the Yb doping concentration reaches to as high as 27.1at.% for Yb:YAG. Under 940nm excitation, the influence of the self-absorption at 969 and 1029nm on the fluorescence spectra is not evident when the Yb doping concentration is as high as 27.1at.%. However, it can greatly change the shape of fluorescence spectra of Yb:YAG when the Yb doping concentration reaches to above 53.6at.%. [Copyright &y& Elsevier]

Abstract: Yb3Al5O12 single crystal has been grown by Czochralski (CZ) method. The absorption spectrum was investigated at low temperature and the electronic energy levels for 2F5/2 multiplet of Yb3+ in YbAG was proposed. The up-conversion emission of the crystal under 940nm diode pumping and the X-ray excited luminescence (XEL) features of the crystal were also studied. [Copyright &y& Elsevier]

2 at.% Tm, xat.% Dy:Y 2 O 3 (x = 0, 0.1, 0.5 and 1) transparent ceramics were fabricated via vacuum sintering. The microstructural properties of the prepared ceramics were determined using XRD and SEM. The absorption cross-section of 2 at.% Tm, 1 at.% Dy:Y 2 O 3 ceramic was 0.53 × 10−20 cm2 with the FWHM of 43.59 nm. The increased cross-section originates from a large overlapping range appearing in the absorption spectrum of the Dy3+:6H 15/2 → 6F 5/2 and Tm3+:3H 6 →6H 4 transitions. The J-O intensity parameters Ω 2 , Ω 4 and Ω 6 and the fluorescence characteristics of the pivotal luminescent level of the Dy3+ ions were investigated. Under 793 nm excitation, the emission cross section of the Tm,Dy:Y 2 O 3 ceramic at 3094 nm was 3.63 × 10−21 cm2 with the FWHM of 355 nm. The fluorescence lifetimes of Dy3+:6H 13/2 level of 2 at.% Tm, xat.% Dy:Y 2 O 3 (x = 0.1, 0.5 and 1) ceramics were fitted to be 357 μs, 282 μs and 149 μs, respectively. In order to explore the quenching mechanism of Tm3+:3F 4 level, the fluorescence lifetimes of Tm3+:3F 4 of the 2 at.% Tm, xat.% Dy:Y 2 O 3 ceramics (x = 0, 0.1, 0.5 and 1) were measured to be 4.878 ms, 462 μs, 104 μs and 61 μs, respectively. The possible energy transfer mechanisms between Tm3+ and Dy3+ ions are discussed. The results show that adding Tm3+ ions to Dy:Y 2 O 3 ceramics can effectively enhance the 2.9 μm MIR through energy transfer. [ABSTRACT FROM AUTHOR]

Ho,Pr:CaYAlO 4 (Ho,Pr:CYA) crystal doped with 1 at.% Ho3+ and 0.1 at.% Pr3+ was successfully grown using the Czochralski method. Polarized absorption spectra, emission spectra, and fluorescence lifetime measurements were performed. The impact of Pr3+ co-doping on the ∼3 μm emission of Ho3+ ions was analyzed. The energy transfer efficiency from Ho3+:5I 7 to Pr3+:3F 2 energy level was calculated to be 60.66 %, indicating that Pr3+ effectively mitigated the self-termination effect in Ho,Pr:CYA crystals. The absorption cross-section at 645 nm was found to be 1.53 × 10−20 cm2 for σ polarization and 2.62 × 10−20 cm2 for π polarization. The emission cross-section at 2842 nm was calculated to be 0.86 × 10−20 cm2 for σ polarization and 1.33 × 10−20 cm2 for π polarization at 2908 nm, with a full width at half maximum (FWHM) of 139 nm and 88 nm, respectively. The fluorescence lifetimes of the 5I 6 and 5I 7 levels were measured to be 0.17 ms and 2.01 ms, respectively. These results collectively suggest that Ho,Pr:CYA crystals hold great potential as a candidate for 2.8 μm laser applications. • Ho3+,Pr3+ co-doped CaYAlO 4 crystal was grown by the Czochralski method. • The crystal structure, polarized absorption and emission spectra were investigated. • The intensity parameters were obtained using J-O theory. [ABSTRACT FROM AUTHOR]

Abstract: A high optical quality erbium doped Lu2SiO5 single crystal has been grown by the Czochralski method. The distribution coefficient of Er3+ was measured to be ∼0.926. The absorption and emission spectra as well as the fluorescence decay curve of the excited state 4I13/2 were measured at room temperature. The spectroscopic parameters were calculated using the Judd–Ofelt theory, and the J–O parameters Ω 2 , Ω 4 and Ω 6 were found to be 4.451×10-20, 1.614×10-20 and 1.158×10-20 cm2, respectively. The room-temperature fluorescence lifetime of the Er3+ 4I13/2→4I15/2 transition was measured to be 7.74ms. The absorption and emission cross-section as well as the gain cross-section in the eye-safe regime of 1400–1700nm were also determined and discussed. [Copyright &y& Elsevier]

The high optical quality 5 at% doped Yb:YAG single crystals with diameter of 3 inches have been grown by temperature gradient technology (TGT). The segregation coefficient of Yb ions in TGT-grown 5 at% doped Yb:YAG crystals determined by ICP-AES method is equal to 1.1. The absorption spectra in the range of 190–1200 nm of TGT-grown Yb:YAG crystals were also measured at the room temperature. The absorption peaks of trivalent Yb ions and the unknown color centers were found in the absorption spectra. [Copyright &y& Elsevier]

Tm3+-doped CaY 0.9 Lu 0.1 AlO 4 single crystal was successfully grown by the Czochralski method. The crystal structure, polarized absorption spectra and polarized emission spectra of Tm:CaY 0.9 Lu 0.1 AlO 4 crystals were investigated. By using the Judd–Ofelt approach, the intensity parameters Ω 2,4,6 , spontaneous transition rate, branching ratios and radiative lifetimes were calculated. Diode-end-pumped continuous-wave Tm:CaY 0.9 Lu 0.1 AlO 4 lasers have also been investigated by establishing a simple and compact plane-concave cavity with four differently coated output couplers. Four different lasing wavelengths at about 2029 nm, 2000 nm, 1966 nm and 1888 nm have been achieved with maximum output power and slope efficiency of (1.98 W, 15.1%), (5.89 W, 46.2%), (6.92 W, 54.9%) and (5.54 W, 44.7%), respectively. The results in regard to the broad emission spectra and good laser performance show that the Tm:CaY 0.9 Lu 0.1 AlO 4 mixed crystal could be very promising for broadband tunable and/or femtosecond ultrafast laser generation in the important 2-μm spectral region. • Tm:CaY 0.9 Lu 0.1 AlO 4 crystal was grown by the Czochralski method. • The crystal structure, polarized spectra were investigated. • The maximum output power of 6.92 W with slope efficiency 54.9% was achieved. [ABSTRACT FROM AUTHOR]

Tm3+-doped calcium niobium gallium garnet (Tm:CNGG) single crystals have been successfully grown by the micro-pulling-down (μ-PD) method. The crystal structure, absorption spectra, fluorescence spectra and lifetimes of Tm:CNGG crystals were investigated. The absorption and emission bandwidths of Tm:CNGG crystals are larger than those of other Tm3+ doped garnet crystals, which will be beneficial for laser diode (LD) pumping and ultrashort pulse generation. Additionally, continuous wave (CW) laser operation around 2 μm was achieved in the 2.0 at.% Tm:CNGG crystal by LD pumping. [ABSTRACT FROM AUTHOR]

Sm3+ doped yttria transparent ceramics (Sm x Y 1-x) 2 O 3 (x = 0.01, 0.015, 0.03) were fabricated by Spark Plasma Sintering method. Absorption spectra, as well as emission spectra and luminescence lifetime were carried out at room temperature. Judd-Ofelt (J-O) theory was used to calculate the Ω t (t = 2, 4, 6) intensity parameters. The spontaneous transition probabilities, radiative lifetime, branching ratio, and stimulated emission cross-sections have been calculated for 4G 5/2 excited level. The emission cross section for the 4G 5/2 → 6H 7/2 transition at about 607 nm was calculated to be 6.73 × 10−22 cm2. The results indicate that Sm:Y 2 O 3 ceramic may be a potential reddish orange-light laser material around 607 nm. [ABSTRACT FROM AUTHOR]

YScO 3 single crystal co-doped with Ho3+ and Pr3+ ions has been successfully grown by the Czochralaki method. The absorption spectrum, fluorescence spectrum and fluorescence decay curve were measured at room temperature. The absorption cross section of Ho,Pr:YScO 3 at 649 nm and 1130 nm was calculated to be 0.93 × 10−20 cm2 and 0.32 × 10−20 cm2, respectively. Judd-Ofelt (J-O) theory was performed to evaluate the spontaneous emission probabilities and the radiative lifetimes. Ho,Pr:YScO 3 exhibited strong emission at 2040 nm and 2890 nm with a emission cross section of 0.80 × 10−21 cm2 and 1.22 × 10−20 cm2, respectively. The fluorescence lifetime of the Ho3+:5I 6 and 5I 7 levels were calculated to be 0.31 ms and 5.89 ms, respectively. All the results indicate that the Ho,Pr:YScO 3 crystal could be a potential laser material for 2.9 μm laser operation. • Ho3+,Pr3+ co-doped YScO 3 was grown by the Czochralski method. • The crystal structure, absorption and emission spectra were investigated. • The effect of Pr3+ on the spectroscopic properties of Ho3+ was evaluated. [ABSTRACT FROM AUTHOR]

Pr3+-doped Sr 0.5 La 0.5 Mg 0.5 Al 11.5 O 19 (ASL) crystal along 〈100〉 direction was successfully grown using the Czochralski technique under azote atmosphere. Absorption and emission spectra of Pr:ASL crystal have been measured at room temperature. Continuous-wave laser operation of the a-cut and c-cut Pr:ASL samples under InGaN laser diode pumping has been demonstrated. For deep red laser operation at about 726 nm, the maximum output powers achieved from a-cut sample was 92.8 mW with slope efficiency of about 11.9%, while 46.6 mW with slope efficiency of 8.0% for the c-cut sample. For red laser at about 645 nm, maximum output powers of 49.2 mW and 42.8 mW were obtained for the a-cut sample and c-cut sample, corresponding to a slope efficiency of 6.7% and 8.5%, respectively. • Pr:Sr 0.5 La 0.5 Mg 0.5 Al 11.5 O 19 crystal was successfully grown using the Czochralski method. • Spectral parameters of Pr:Sr 0.5 La 0.5 Mg 0.5 Al 11.5 O 19 crystal were obtained. • Red and deep red laser were demonstrated in Pr:Sr 0.5 La 0.5 Mg 0.5 Al 11.5 O 19 crystal. [ABSTRACT FROM AUTHOR]

Abstract We report on the growth, spectroscopic properties and visible laser operation of Pr3+-doped LaMgAl 11 O 19 (LMA) crystal. The absorption and emission spectra were recorded in visible wavelength range and the decay time of 3P 0 manifold was measured to be about 34.5 μs at room temperature. Using an InGaN laser diode as pump source, continuous-wave laser operation of Pr:LMA crystal have also been demonstrated in red at about 645 nm and deep red at about 725 nm, which provide new linearly polarized sources for various potential applications. Highlights • A Pr:LMA crystal was successfully gown by using the Czochralski method. • Spectral parameters of Pr:LMA crystal were obtained. • Using a blue laser diode as pump source, red and deep red laser were demonstrated from Pr:LMA crystal. [ABSTRACT FROM AUTHOR]

Abstract Nd3+-doped Bi 4 Ge 3 O 12 (Nd:BGO) single crystals have been successfully grown by the micro-pulling-down (μ-PD) method. The absorption spectra, fluorescence spectra and fluorescence decay curve have been measured at room temperature. The absorption cross section is about 1.39 × 10–20 cm2 at around 808 nm for 0.3 at% Nd:BGO. The Judd–Ofelt theory has been applied to calculate the intensity parameters, and three spectroscopic parameter Ω t (t = 2,4,6), radiative transition probabilities, radiative lifetime and branching ratios were calculated. The stimulated emission cross-section of 4F 3/2 →4I 11/2 transition at 1064 nm was obtained to be 3.29 × 10–20 cm2 for 0.3 at% Nd3+-doped BGO crystal. The fluorescence lifetimes of 0.3 at% and 1.0 at% neodymium-doped BGO crystals were measured to be 288 μs and 242 μs, respectively. Those results indicate that Nd3+-doped BGO crystal grown by the μ-PD method would be a potential laser medium. [ABSTRACT FROM AUTHOR]

Abstract We report on diode-pumped continuous-wave and passively Q-switched c-cut Nd:LMA lasers. For continuous-wave operation, the maximum output power reaches 3.10 W with slope efficiency of about 48.9% at 1055 nm and 2.63 W with slope efficiency of 43.1% at 1082 nm. For passively Q switched operation, using a Cr:YAG as saturable absorber, the achieved maximum average output power is 1.49 W at 1055 nm with pulse width of 18.4 ns. Moreover, we have also realized simultaneous dual-wavelength laser operation at 1055 and 1082 nm with a maximum average output power of 1.22 W and a pulse width of 19.4 ns. Furthermore, inserting an etalon for suppressing the 1055 nm line, we have operated single wavelength laser at 1082 nm with output power of 0.31 W and pulse width of 20.8 ns. This work has verified the potential of Nd:LMA crystal as a laser gain medium. Highlights • Absorption and emission spectra of a c -cut Nd: LaMgAl 11 O 19 crystal are reported. • Efficiently continuous-wave operation at 1055 and 1082 nm have been realized for the first time to our knowledge. • Efficiently passively Q-switched operation at 1055 and 1082 nm have also been realized. [ABSTRACT FROM AUTHOR]

The luminescence properties of 0.5%Pr-doped BGO crystals grown by using the micro-pulling down technique were carefully investigated. Room temperature absorption spectra were registered and analyzed within the framework of the Judd-Ofelt formalism and the best fit to the data is obtained by using a modified treatment allowing for the admixture of intensity enabling wave-functions. The results indicate 3P 0 and 1D 2 radiative lifetimes of about 5.7 μs and 79 μs, in perfect agreement with the time-constants derived from the measured fluorescence decays at room and liquid-nitrogen temperatures. Registration of time-resolved emission and excitation spectra and calibration of the 3P 0 emission spectrum in cross section unit clearly indicate that Pr-doped BGO could be the first isotropic crystalline material leading to efficient diode-pumped laser operation at room temperature with laser performances, at least in the deep-red spectral region, comparable to that found with the most important anisotropic Pr-doped fluoride and oxide crystals. • Pr:Bi 4 Ge 3 O 12 crystal fibers are successfully grown by micro-pulling down. • Absorption spectra are analyzed by using the Judd-Ofelt formalism. • Emission, excitation spectra are registered from the near-UV to the deep-Red. • It is found a 3P0 emission lifetime of 5.7 μs for a quantum yield close to 1. • Record emission cross-sections are obtained in the red and deep-red. [ABSTRACT FROM AUTHOR]

Tb 3+ -doped YAlO 3 (YAP) single crystal was grown by Czochralski (Cz) method. Based on the polarized absorption spectra, the spectroscopic parameters were calculated to be Ω 2 = 3.49 × 10 −20 cm 2 , Ω 4 = 5.87 × 10 −20 cm 2 and Ω 6 = 2.55 × 10 −20 cm 2 , and then the spontaneous transition rate, fluorescent branching ratio and radiative lifetime of 5 D 4 multiplet were obtained. The yellow emission cross sections of 5 D 4 → 7 F 4 transition were calculated to be 1.72 × 10 −22 cm 2 , 2.73 × 10 −22 cm 2 and 2.65 × 10 −22 cm 2 for a, b and c polarization, respectively. The fluorescence lifetime of the 5 D 4 multiplet was fitted to be 1.72 ms. All the data indicate that Tb:YAP crystal is a promising candidate for yellow laser operation. [ABSTRACT FROM AUTHOR]

The polarization absorption spectra of Pr3+-doped GdScO 3 have been measured. Polarized emission spectra and fluorescence decay from the 3P 0 upper level have been investigated. The strongest absorption peaks are located at 448 nm for a, b and c polarization, the absorption cross sections are 1.29 × 10−20 cm2, 0.98 × 10−20 cm2 and 1.57 × 10−20 cm2, respectively. The maximum emission cross section is located at 662 nm, which is 18.55 × 10−20 cm2 (a polarization), 12.74 × 10−20 cm2 (b polarization) and 22.41 × 10−20 cm2 (c polarization), and the FWHM is 10.02 nm, 9.38 nm and 10.14 nm, respectively. The fluorescence lifetime of 3P 0 level is 12.39 μs. Those results indicated that Pr3+-doped GdScO 3 crystal grown by the Czochralski method is a potential laser medium for visible laser operation. •The spectra of Pr:GdScO 3 have been measured at room temperature. •Pr3+-doped GdScO 3 crystal is a potential laser medium for 662 nm laser. [ABSTRACT FROM AUTHOR]

Ho3+-doped CaY 0.9 Gd 0.1 AlO 4 single crystal was successfully grown by the Czochralski technique for the first time. The polarized absorption spectra, polarized luminescence spectra and fluorescence decay curve of the crystal were investigated at room temperature. The spectroscopic parameters are calculated based on Judd–Ofelt theory, the values of Ω 2,4,6 were calculated to be 3.16 × 10−20 cm2, 3.93 × 10−20 cm2, 0.91 × 10−20 cm2, respectively. The Ho:CaY 0.9 Gd 0.1 AlO 4 crystal exhibits strong emission at 2013 nm for π- and 2032 nm for σ-polarizations with stimulated emission cross section of 6.64 × 10−20 cm2 and 1.90 × 10−20 cm2, respectively. The fluorescence lifetime of the 5I 7 level was measured to be 6.60 ms. The continuous-wave (CW) laser operation of Ho:CaY 0.9 Gd 0.1 AlO 4 crystal around 2 μm was demonstrated. • Ho3+-doped CaY 0.9 Gd 0.1 AlO 4 single crystal was successfully grown by the Czochralski technique for the first time. • The emission cross-section at 2013 nm and 2032 nm are 6.64 × 10−20 cm2 and 1.90 × 10−20 cm2 for π- and σ-polarizations respectively. • The continuous-wave (CW) laser operation of Ho:CaY 0.9 Gd 0.1 AlO 4 crystal around 2 μm was demonstrated. [ABSTRACT FROM AUTHOR]

A series of 0.5 at.% Tm:Ca 1-x Y x F 2+x (x = 0, 0.01, 0.04, 0.06, 0.08, 0.12) crystals have been successfully grown by the temperature gradient technique (TGT) method. The absorption spectra, fluorescence spectra, and fluorescence decay curves were measured and analyzed at room temperature. By comparison, it is found that when the concentration of Y3+ ions reaches 8 at.%, the absorption cross section corresponding to the 3H 6 →3H 4 energy level is 2.56 × 10−21 cm2 at 793 nm, which is suitable for GaAlAs LD pumping. The J-O strength parameters Ω 2 , Ω 4 , and Ω 6 were obtained. With the incorporation of Y3+ ions, the value of Ω 4 /Ω 6 gradually increases. When the concentration of Y3+ ions reaches 8 at.%, the emission cross sections are 3.05 × 10−21 cm2 at 1476 nm, 2.56 × 10−21 cm2 at 2378 nm, and the full widths at half maximum (FWHM) are 76 nm and 195 nm, respectively. The fluorescence lifetime of 3H 4 level, the upper level of 1.5 μm and 2.3 μm, is 1.05 ms, which is very beneficial for 1.5 μm and 2.3 μm laser. • With the incorporation of Y3+ ions, the value of Ω 4 /Ω 6 gradually increases. • When the concentration of Y3+ ions reaches 8 at.%, the emission cross section is 3.05 × 10−21 cm2 at 1476 nm, 2.56 × 10−21 cm2 at 2378 nm, respectively. • The fluorescence lifetime of 3H 4 level, the upper level of 1.5 μm and 2.3 μm, is 1.05 ms, which is very beneficial for 1.5 μm and 2.3 μm laser. [ABSTRACT FROM AUTHOR]

• The stable CW ML pulsed with pulse duration as short as 1.97 ps was experimentally obtained. • We proved it experimentally that under the increasing saturation parameters , output pulses could be narrowed in the steady state cavity. • We used the generalized Ginzburg-Landau equation for the mode-locked pulse dynamic evolutions. • We showed that the pulse-narrowing mechanism in solid-state cavity at water absorption band. Ultrafast solid-state laser sources operating in the mid-infrared (mid-IR) region are of significant importance in a variety of applications. However, the realization of ultrafast lasers with narrow pulse width at wavelengths between 1.8 and 2 µm has remained a big challenge due to the strong water molecule absorption. Here, we report a stable mode-locking (ML) pulsed lasing at 1967 nm and narrow pulse duration of 1.97 ps in a diode-pumped Tm:CaYAlO 4 (Tm:CYA) crystal laser oscillator. By employing the SESAMs with different modulation depths as mode-lockers, we show that under the increasing saturation parameters, output pulses could be narrowed in the steady state cavity. Furtherly, the generalized Ginzburg-Landau equation is used for the mode-locked pulse dynamic evolutions. It shows that the pulse- regulation mechanism in solid-state cavity at water absorption band is governed by the balance of the laser gain, the modulation depth, and the saturation parameter. To our knowledge, this is the first demonstration of pulse regulation mechanism in the 2 μm water absorption band by a commercial laser diode in a Tm:CYA laser. Our results provide an effective method for pulse regulation of ultra-short mid-IR pulses and even few-cycle pulses with controllable optical spectra in the water absorption band. [ABSTRACT FROM AUTHOR]

Yb,Tb:YAG crystals with various Yb3+ and Tb3+ concentration were grown by the micro-pulling-down method (μ -PD). The absorption spectra, fluorescence spectra and fluorescence decay curves of Yb,Tb:YAG crystals were measured at room temperature. Under 980 nm excitation, Yb,Tb:YAG crystals exhibited intense visible up-conversion luminescence due to the cooperative energy transfer from two Yb3+ ions to one Tb3+ ion. Under 485 nm excitation, Yb,Tb:YAG crystals yielded near-infrared down-conversion emission, ascribing to the cooperative absorption of pumping photons and cooperative energy transfer from one Tb3+ ion to two Yb3+ ions. The energy transfer processes from Yb3+ ions to Tb3+ ions were discussed, and the energy transfer efficiency was calculated. Based on studies of the obtained results, Yb3+/Tb3+ co-doped YAG crystal shows promising potential for sensing, volumetric displays, optical data storage, light emitting diodes. • Yb,Tb:YAG single crystals grown by the micro-pulling-down technique. • The cooperative energy transfer process was analyzed. • The effect of doped concentration on energy transfer efficiency was discussed. [ABSTRACT FROM AUTHOR]

• After co-doping Tb3+ ions, the Ω4/Ω6 increased 1.57 from to 1.66. • The branching ratios of the 3H 4 →3F 4 transition also strengthened. • The decay curve of 3F 4 level doped with different Tb3+ ions concentration decreased. • Tb3+ ion is a productive deactivator that could reduce the filling of 3F 4 mainfold and enhance the emission of 3H 4 →3F 4 transition. Tm3+ and Tb3+ co-doped Y 3 Al 5 O 12 (YAG) ceramics were fabricated by high temperature solid state reaction under oxygen sintering. The absorption spectra, fluorescence spectra and fluorescence decay curves of Tm,Tb:YAG ceramics were measured. The spectral parameters of Tm,Tb:YAG ceramic were calculated. The lifetimes of Tm3+:3F 4 level of Tm,Tb:YAG ceramics were calculated to be 11.28, 2.12, 1.24, 0.63 and 0.49 ms for the Tb3+ doping concentration of 0, 0.1, 0.2, 0.35 at 0.5 at%, respectively. The co-doping Tb3+ ion is a productive deactivator that could reduce the filling of 3F 4 mainfold and enhance the emission of 3H 4 →3F 4 transition. These results indicate that the addition of Tb3+ ions in Tm,Tb:YAG ceramic could be a promising technique for laser operation around 1.5 µm. [ABSTRACT FROM AUTHOR]

Tm3+-doped bismuth germanate crystals (Tm:BGO) with various doping concentrations of 0.5, 0.75, 1.0, 1.5, and 2.0 at.% were grown by the micro-pulling-down method (μ-PD). The effect of thulium concentration on the growth, structure, absorption spectra, emission spectra and fluorescence lifetime of 3H 4 and 3F 4 state was studied. Under excitation of 792 nm, Tm:BGO crystals exhibit two fluorescence bands corresponding to the 3H 4 → 3F 4 and the 3F 4 → 3H 6 transitions. The fluorescence lifetime of 3H 4 state decreased strongly as the thulium concentration increased, while the lifetime of 3F 4 state was relatively constant for all thulium concentrations. • Tm:BGO crystals with different Tm3+ concentration were grown by the micro-pulling-down method. • The effect of Tm3+ concentration on the growth, structure and spectroscopic properties of Tm:BGO crystals was studied. • Tm:BGO crystals exhibit two fluorescence bands corresponding to the 3H 4 → 3F 4 and the 3F 4 → 3H 6 transitions. [ABSTRACT FROM AUTHOR]

Tm3+ doped and Tm3+, Pr3+ co-doped Lu 3 Al 5 O 12 (LuAG) garnet single crystals have been successfully grown by the micro-pulling-down (μ-PD) method. The absorption spectra, fluorescence spectra and lifetimes were investigated at room temperature. In the absorption spectra, the transition centered at 782 nm matches well with the GaAlAs LDs laser pumping. The incorporation of Pr3+ into Tm3+-doped LuAG crystals enhanced the intensity of 1.5 μm emission and decreased the fluorescence lifetime of the lower energy level for 1.5 μm emission from 10.427 ms to 2.603 ms. The results indicate that Tm,Pr:LuAG crystal can be promising candidate for near infrared 1.5 μm laser materials. • Tm:LuAG and Tm,Pr:LuAG crystals have been successfully grown by the micro-pulling-down (μ-PD) method. • Spectral parameters of Tm:LuAG and Tm,Pr:LuAG crystals were obtained and compared. • The fluorescence mechanism of Tm,Pr:LuAG crystal has been studied for the first time. [ABSTRACT FROM AUTHOR]

Nd:SrAl 11 O 19 (Nd:SRA) crystal has been grown by the Czochralski method. Polarized absorption spectra, polarized fluorescence spectra and fluorescence lifetime were investigated. For σ-polarization, the peak absorption cross section at 798 nm is 2.08 × 10−20 cm2 with full width at half maximum (FWHM) of 10.2 nm and the peak emission cross section is 3.36 × 10−20 cm2 at 1048.5 nm with FWHM of 4.80 nm. The Judd-Ofelt parameters Ω 2,4,6 were obtained to be 0.51 × 10−20 cm2, 2.08 × 10−20 cm2, and 2.12 × 10−20 cm2, respectively. Continuous-wave laser operation of the a-cut and c-cut Nd:SRA sample has been demonstrated. The maximum output power of 8.33 W was achieved from c-cut sample at an absorbed power of 27.73 W, corresponding to a slope efficiency of 31.3%. • Nd:SrAl 12 O 19 crystal has been gown by the Czochralski method. • Spectral parameters of Nd:SrAl 12 O 19 crystal were obtained. • Continuous-wave laser was demonstrated from Nd:SrAl 12 O 19 crystal. [ABSTRACT FROM AUTHOR]

Yb,Pr:CaF 2 crystals have been grown successfully by the temperature gradient technique(TGT). The absorption spectra, fluorescence spectra, fluorescence decay lifetime of Pr3+ ions in CaF 2 crystal sensitized by different Yb3+ ions concentration have been measured. The effective J-O intensity parameters were fitted to be Ω 2 =0.36 × 10−20cm2, Ω 4 =2.89 × 10−20cm2, Ω 6 =6.69 × 10−20cm2 for 0.3 at.%Pr,1.5 at.%Yb:CaF 2. And the emission cross sections of 3P 1 →3H 5 (535 nm), and 3P 0 →3F 4 (750 nm) are calculated to be 2.02 × 10−20cm2, and 2.50 × 10−20cm2 with the FWHM of 17.2 nm, and 10.5 nm, respectively. The fluorescence lifetime of 3P 0 has achieved great increasing by sensitizing of Yb3+ ion. Not only the up-conversion luminescence can be achieved, but also the broad band emission from 1D 2 energy level can be observed. The results show that Yb,Pr:CaF 2 could be a potential laser gain medium for visible and near-IR laser operation. • Not only the up-conversion luminescence can be achieved, but also the broad band emission from 1D 2 energy level can be observed by Yb3+ ion sensitizing. • Spectral properties and Judd-Ofelt parameters of Yb,Pr:CaF 2 crystal were investigated and analysed. [ABSTRACT FROM AUTHOR]

Yb,Ho:Y 2 O 3 ceramics have been fabricated by Spark Plasma Sintering method (SPS). The microstructure and transmittance of the ceramics sintered from 1623 K to 1673 K were analyzed. The highest in-line transmittance of Yb,Ho:Y 2 O 3 ceramic sintered at 1673 K reached almost 83% at 750 nm with the thickness of 1 mm. The absorption spectra, fluorescence spectra and fluorescence decay curve were recorded at room temperature. The Judd-Ofelt parameters Ω 2 , Ω 4 and Ω 6 were calculated to be 8.33 × 10−20 cm2, 1.81 × 10−20 cm2, and 0.82 × 10−20 cm2, respectively. The intense emission cross section of Yb,Ho:Y 2 O 3 ceramic was 3.43 × 10−20 cm2 at 2057 nm with full width at half maximum (FWHM) of 208 nm. The results indicate that Yb,Ho:Y 2 O 3 transparent ceramic can be a promising laser gain medium for laser operation around 2 μm. Image 1 • The highest in-line transmittance of Yb,Ho:Y 2 O 3 ceramic sintered at 1673 K reached almost 83% at 750 nm with the thickness of 1 mm. • The spectral characteristics were intensively investigated through Judd-Ofelt theory. [ABSTRACT FROM AUTHOR]

Photograph of Yb,Ho:YAG crystals grown by the μ-PD method. (a) Yb = 0.05, (b) 0.1, (c) 0.15. • Y 3 Al 5 O 12 (YAG) single crystals doped with a fixed Ho3+ content of 0.5 at.% and various Yb3+ contents (Yb = 5, 10 and 15 at.%) have been successfully grown by the micro-pulling-down (μ-PD) method. Y 3 Al 5 O 12 (YAG) single crystals doped with a fixed Ho3+ content of 0.5 at.% and various Yb3+ contents (Yb = 5, 10 and 15 at.%) have been successfully grown by the micro-pulling-down (μ-PD) method. The absorption spectra, fluorescence spectra and fluorescence decay curves were recorded at room temperature. The intense emission of Yb,Ho:YAG crystal centered at 2 μm corresponds to the 5I 7 → 5I 8 transition. Three intense emissions centered at 524–569 nm, 623–691 nm and 744–746 nm, correspond to the 5F 4 + 5S 2 → 5I 8 , 5F 5 → 5I 8 and 5F 4 + 5S 2 → 5I 7 transitions, respectively. The possible energy transfer mechanisms were discussed intensively. [ABSTRACT FROM AUTHOR]

We report on the comparative growth and spectroscopy of Eu3+-doped Y 3 Al 5 O 12 (YAG) and Y 3 ScAl 4 O 12 crystals grown by the micro-pulling-down (μ-PD) method. The structure of the as-grown crystals was determined by X-ray diffraction (XRD) and Raman spectroscopy. The absorption spectra of the crystals are dominated by a strong line centered at 395 nm, matching well with the emission of commercial ultraviolet laser diodes. The Eu:YAG and Eu:Y 3 ScAl 4 O 12 crystals exhibit strongest red emission centered at 710 nm and the full width at half maximum (FWHM) was calculated to be 2.03 and 3.19 nm, respectively. The fluorescence decay curves of 5D 0 levels were measured and discussed. All the results indicate that the Eu:YAG and Eu:Y 3 ScAl 4 O 12 crystals are promising candidates for red luminescent/laser materials. • Eu:YAG and Eu:Y 3 ScAl 4 O 12 crystals were successfully grown by the micro-pulling-down technique for the first time. • The structure parameters of Eu:YAG and Eu:Y 3 ScAl 4 O 12 crystals were investigated by XRD. • Spectral parameters of Eu:YAG and Eu:Y 3 ScAl 4 O 12 crystals were obtained and compared. [ABSTRACT FROM AUTHOR]

High quality of Tb3+-single doped and Tb3+/Pr3+ co-doped CaF 2 crystals were grown by the temperature gradient technique (TGT). Pr3+ ions were used as sensitizing ions of Tb3+. Optical properties including absorption spectrum, emission spectrum, and fluorescence decay curve were recorded. Through co-doping sensitizing ions of Pr3+, the absorption cross section around 480 nm increased from 0.007 × 10−20 cm2 to 0.3 × 10−20 cm2, the large value is beneficial for the absorption of LD pump source. Judd-Ofelt theory was used to analyze the spectroscopic parameters. Fluorescence branch ratio, transition probability, radiative and fluorescence lifetimes, and quantum efficiency were determined as well. The emission cross section of Tb,Pr:CaF 2 for the green emission at 544 nm and yellow emission at 587 nm corresponding to the transition of 5D 4 →7F 5 and 5D 4 →7F 4 were calculated to be 5.56 × 10−22 cm2 and 8.78 × 10−23 cm2, respectively, which is comparable to the Tb3+ doped CaF 2 crystal. • Tb:CaF 2 crystal and Tb/Pr co-doped CaF 2 crystal were grown by TGT method. • Pr3+ ions were used to improve the absorption cross section of Tb3+ ions. • Judd-Ofelt theory was used to analyze the spectroscopic parameters. • Tb,Pr:CaF 2 crystal is a potential laser material for green and yellow oscillation. [ABSTRACT FROM AUTHOR]

LaMgAl 11 O 19 (LMA) crystal with nominal Sm3+ concentrations of 8 at.% was grown by the Czochralski method. Polarized absorption spectra, polarized emission spectra and fluorescence decay curve of Sm:LMA crystal were recorded at room temperature. The absorption cross-sections at 404 nm were calculated to be 2.33 × 10−20 cm2 and 0.86 × 10−20 cm2 for σ and π polarization, respectively. The spontaneous transition rates, branching ratios and the radiative lifetime of the 4G 5/2 multiplet, were calculated. The Judd-Ofelt theory has been applied to evaluate the Ω t (t = 2, 4, 6) intensity parameters. The highest stimulated emission cross-sections for the 4G 5/2 → 6H 7/2 transition around 594 nm were calculated to be 1.67 × 10−21 cm2 for σ polarization and 1.15 × 10−21 cm2 for π polarization, with full width at half maximum (FWHM) of 7.68 nm and 7.27 nm, respectively. The fluorescence lifetime of the 4G 5/2 manifold was 1.84 ms. All the results show that Sm:LMA crystal would be a promising orange-red solid state laser material. • The most intensive absorption line of Sm3+ ion, suitable for 405 nm InGaN laser diode. • The rigidity of Sm:LMA crystal is higher than some host crystals. • The value Ω 2 of Sm:LMA crystal is comparable to Sm:LiYF 4. • The large parameter σ em τ of Sm3+ in LMA is beneficial for the solid state laser. [ABSTRACT FROM AUTHOR]

Dy3+-doped Y 3 Al 5 O 12 (YAG) and Y 3 ScAl 4 O 12 (YSAG) single crystals have been successfully grown by the micro-pulling-down (μ-PD) technique for the first time. The room temperature absorption spectra, fluorescence spectra and fluorescence decay curves were measured. Dy:YAG and Dy:Y 3 ScAl 4 O 12 crystals exhibit strongest emission centered at 583 nm, corresponding to the 4F 9/2 → 6H 13/2 transition. The decay lifetime of the 4F 9/2 level was measured to be 634 μs and 667 μs, respectively. All these results indicate that the Dy:YAG and Dy:Y 3 ScAl 4 O 12 crystals are promising candidates for yellow laser operation. • Dy:YAG and Dy:YSAG crystals were grown by the micro-pulling-down method. • Dy:YAG and Dy:YSAG crystals exhibit strong emission centered at 583 nm. • Dy:YSAG crystal has a wide emission bandwidth due to the disordered crystalline structure. [ABSTRACT FROM AUTHOR]