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Nd 3+ sensitized Er 3+ : 4 I 11/2 → 4 I 13/2 mid-infrared (MIR) emission around 2.7 μm was achieved in SrGdGa 3 O 7 single crystal for the first time. The effect of Nd 3+ on the absorption, near-infrared (NIR) and MIR fluorescence properties of Er 3+ ions were investigated. It is found that Nd 3+ greatly improves the absorption pump efficiency and thus enhances the Er 3+ ~2.7 μm emission by nearly 10 times under 808 nm laser diode (LD) excitation, at the same time quenches the ~1.5 μm near-infrared emission of the lower level Er 3+ : 4 I 13/2 and thus suppresses the self-saturation problem effectively. The luminescent mechanism for the Nd 3+ /Er 3+ :SrGdGa 3 O 7 crystal was analyzed and the possible energy transfer processes were proposed. The energy transfer efficiencies of Nd: 4 F 3/2 →Er: 4 I 11/2 and Er: 4 I 13/2 →Nd: 4 I 15/2 are estimated to be 85.8% and close to 100%, respectively. The results indicate that the introduction of Nd 3+ is very beneficial in achieving 2.7 μm laser in Er 3+ :SrGdGa 3 O 7 crystal which could act as a potential gain media for LD pumped MIR laser. [ABSTRACT FROM AUTHOR]

Crack-free Sr(MoO 4 ) x (WO 4 ) 1− x ( x = 0.3, 0.45, 0.7) solid solution single crystals with high optical quality and large dimensions have been successfully grown by the Czochralski method for the first time. The unit cell parameters and the density change linearly on the composition x that all obey Vegard’s law, indicating an ideal isomorphous substitution of W 6+ by Mo 6+ . The refractive index functions and the average thermal expansion coefficients are precisely measured. As the concentration of [MoO 4 ] 2− increases, the refractive indices have a monotonous increasing trend, while the thermal expansion coefficients follow a parabolic trend. In the pontaneous Raman spectra, the double-mode behavior of v 1 (A g ) band has been observed. The Raman shifts at 886 and 921 cm −1 with narrow line widths and high peak intensities indicate Sr(MoO 4 ) 0.45 (WO 4 ) 0.55 crystal a potential uncontested dual-wavelength Raman gain medium. [ABSTRACT FROM AUTHOR]

Yb3+/Tm3+: CaYAlO 4 (CYA) and Nd3+/Yb3+/Tm3+: CYA bulk single crystals were grown using the Czochralski (Cz) method. The polarized absorption, upconversion luminescence (UCL) spectra under 980 nm and 808 nm pumping, and fluorescence decay curves were measured as well as Judd-Ofelt (J-O) theory calculations were performed to investigate the sensitization effect of Yb3+ and Nd3+/Yb3+co-doping in Tm3+: CYA single crystal. Obvious enhancement was observed in Tm3+-activated crystals for the blue upconversion emission (∼474 nm) when doped with Yb3+ or co-doped with Nd3+/Yb3+. The energy transfer efficiency is 72.6% (Yb3+→Tm3+) and 71.7% (Nd3+→Yb3+/Tm3+) in Yb3+/Tm3+: CYA and Nd3+/Yb3+/Tm3+: CYA single crystals respectively. The gain cross-sections were calculated, and it can stated that the blue laser output derived from upconversion is possible around 474 nm related to the transition of 1G 4 → 3H 6 in Yb3+/Tm3+: CYA and Nd3+/Yb3+/Tm3+: CYA crystals. • The bulk single crystals of Yb3+/Tm3+: CaYAlO 4 (CYA) and Nd3+/Yb3+/Tm3+: CYA were grown by Czocharlski (CZ) method. • The upconversion fluorescence properties of Yb3+/Tm3+: CYA and Nd3+/Yb3+/Tm3+: CYA crystals under the pumping of 980 nm and 808 nm were studied specifically. • The energy transfer mechanism from Yb3+ to Tm3+ in Yb3+/Tm3+: CYA crystal and Nd3+ to Yb3+/Tm3+ in Nd3+/Yb3+/Tm3+: CYA crystal was discussed. [ABSTRACT FROM AUTHOR]

Abstract The spectroscopic characteristics of a series of Dy3+/Tm3+-codoped LaF 3 single crystals have been studied for mid-IR emissions through Dy3+:6H 13/2 → 6H 15/2 transition. Optimal mid-IR emission was achieved in 3 at% Tm3+ and 2 at% Dy3+ co-doped LaF 3 sample under the excitation of 790 nm. Its emission cross section was calculated to be 2.56 × 10–21 cm2 at the peak wavelength (2840 nm) with a FWHM of 270 nm, and the fluorescence lifetime was 3.694 ms. The fact of intense 2.84 µm emission was achieved by 790 nm pumping proves the effective energy transfer from Tm3+ to Dy3+ ions. The possible energy transfer routes were analyzed in detail, and the microscopic transfer constants were also estimated based on the phonon-assisted energy transfer theory. As a result, Dy3+/Tm3+-codoped LaF 3 single crystal can be a potential medium for mid-IR lasers. [ABSTRACT FROM AUTHOR]

Er,Eu:YAlO 3 (abbr. as Er,Eu:YAP) crystal was grown by the Czochralski technique for the first time. Its absorption and fluorescence spectra as well as the fluorescence decay curves were measured and investigated. The spectral parameters including absorption cross-section and emission cross-section were calculated. It is found that the crystal has short lifetimes at 4 I 13/2 and 4 I 11/2 levels, large absorption cross-section at 974 nm and 790 nm, and large stimulated emission cross-section at 2704 nm. The co-dopant Eu 3+ decreases the fluorescence lifetime of 4 I 11/2 level from 400 μs to 59.35 μs, and thus inhibits the self-termination effect of ~2.7 μm in some degree. We develop a theoretical model that simulates the laser characteristics of Er,Eu:YAP crystal numerically. Based on Er 3+ -Eu 3+ energy level diagrams, the rate equation model was built and discussed. It was found that: when the pump rate increases gradually, the laser quantum efficiency reaches to its upper limit with a fixed value 2- p 2 , and this value is 1.35 for Er,Eu:YAP crystal. The results show that Er,Eu:YAP crystal is an excellent material candidate for ~2.7 μm laser. [ABSTRACT FROM AUTHOR]

• The Dy3+ singly-doped and Dy3+/Y3+ co-doped SaF 2 single crystals were grown by the Bridgman-Stockbarger method in the self-made medium frequency furnace. • Visible light and mid-infrared spectra properties were studied in detail. • The influence of co-doped Y3+ ions on the spectral properties of Dy3+ ions were discussed. • Dy3+: CaF 2 and Dy3+/Y3+: CaF 2 crystals are expected to achieve yellow and mid-infrared laser output simultaneously. In this work, Dy3+: SrF 2 and Dy3+/Y3+: SrF 2 crystals have been grown successfully by the Bridgman-Stockbarger method, and their absorption spectra, visible and mid-infrared (MIR) emission spectra, as well as fluorescence decay curves were analyzed. The advantages of co-doping Y3+ ions on the yellow and MIR emissions of Dy3+ ions were investigated. The intensity of yellow emission in the doubly-doped crystal is ∼ 4 times stronger than that of the singly-doped crystal. The absorption cross-section (0.782 × 10−21 cm2) at 452 nm and emission cross-section (1.156 × 10−21cm2) at 573 nm of Dy3+/Y3+: SrF 2 crystal is higher than that of Dy3+: SrF 2 crystal related values. Also, compared to Dy3+: SrF 2 crystal, the emission cross-section (3.55 × 10−21 cm2) at 2880 nm and fluorescence decay time (1.062 ms) of Dy3+/Y3+: SrF 2 crystal are found to be higher. When co-doped Y3+ ions, the distance between Dy3+ ions increased leading to the reduction of cross-relaxation and resonant energy transfer probabilities while enhancing the intensities of yellow and MIR emissions. From all the optical results, it can be inferred that Dy3+: SrF 2 and Dy3+/Y3+: SrF 2 crystals are potential materials to simultaneously realize yellow and MIR lasing action. [ABSTRACT FROM AUTHOR]

2 at.% Dy3+: BaF 2 and 2 at.% Dy3+/2 at.% RE3+(RE3+ = Gd3+, Y3+, Lu3+): BaF 2 single crystals were grown by the Bridgman-Stockbarger method, and characterized by absorption, visible emission, and fluorescence decay curves. Also, relying on the excitation and emission spectra, decay curves at low temperature (77 K) for Dy3+: BaF 2 and Dy3+/RE3+(RE3+ = Gd3+, Y3+, Lu3+): BaF 2 crystals have been measured. We found that Dy ions have at least three lattice sites in BaF 2 crystal, and the lattice sites of Dy3+ ions can be reduced by co-doping with Gd3+, Y3+ or Lu3+ ions, where Dy3+: BaF 2 and Dy3+/RE3+(RE3+ = Gd3+, Y3+, Lu3+): BaF 2 single crystals can be considered as quasi-single lattice crystals. From visible fluorescence spectra, it was found that co-doping Gd3+ will increase the emission intensity of yellow light by 20 times, co-doping Y3+ will increase the emission intensity of yellow light by 30 times, and co-doping Lu3+ will increase the emission intensity of yellow light by 25 times. The calculated absorption cross-section, emission cross-section, and fluorescence lifetimes indicate that Dy3+: BaF 2 and Dy3+/RE3+(RE3+ = Gd3+, Y3+, Lu3+): BaF 2 crystals especially, Dy3+/Y3+: BaF 2 crystals are suitable to achieve yellow laser output. • Dy3+: BaF 2 and Dy3+/RE3+(RE3+ = Gd3+, Y3+, Lu3+): BaF 2 crystals are grown. • Dy3+ ion occupies a minimum of three lattice sites in Dy3+: BaF 2 crystal. • Dy3+ ion lattice sites can be reduced by co-doping Gd3+, Y3+, and Lu3+ ions. • Co-doped Gd3+, Y3+, and Lu3+ ions enhance yellow luminescence of Dy3+: BaF 2 crystal. [ABSTRACT FROM AUTHOR]

The Dy3+:SGB single crystal has been successfully prepared for the first time via the Czochralski technique, of which the optical features were investigated in detail. Based on measured polarized absorption spectra, various spectral parameters were determined via Judd-Ofelt theory. The peak absorption cross-sections at 450 nm for the 6H 15/2 → 4I 15/2 transition of Dy3+ ions, are 0.66 × 10−21 cm2 for π-polarization and 0.59 × 10−21 cm2 for σ-polarization respectively. The emission cross-sections at 576 nm are 1.91 × 10−21 cm2 and 1.67 × 10−21 cm2 for π and σ polarizations accordingly. Radiative and fluorescence decay times of Dy3+: 4F 9/2 level were measured to be 1.607 ms and 1.037 ms, respectively, and the quantum efficiency is 64.5%. All experimental results tell that Dy:SGB could be a potential candidate for direct LD-pumped yellow lasers. • First growth of 2 at% Dy3+: Sr 3 Gd(BO 3) 3 crystal and study of spectral properties. • Dy:SGB crystal owns moderate absorption and emission cross-section, with wider FWHM. • The yellow-blue intensity ratio is up to 8.13. • The fluorescence lifetime is relatively larger than other Dy-doped crystals. [ABSTRACT FROM AUTHOR]

Three heavily Er 3+ -doped CaYAlO 4 single crystals were successfully grown by Czochralski method. The emission spectra and the fluorescence decay curves have been recorded at room temperature. A combination of experimental data, rate equation and Dexter theory are used to investigate the influence of Er 3+ doping concentration on the spectra character and the inner cross relaxation of Er 3+ :CaYAlO 4 crystal. Results show that the self terminate effect of the transition 4 I 11/2 → 4 I 13/2 can be suppressed by heavy Er 3+ doping. But if the doping concentration goes too high, the much larger cross relaxation coefficient of 4 I 11/2 level than that of 4 I 13/2 level would results in the increase of up-conversion emission and the quench of near and mid infrared emission. The laser performance was also studied. The maximum output power of 225 mW at 2733 nm was acquired with an optical conversion efficiency of 14.9%. [ABSTRACT FROM AUTHOR]

The intense 2.9 µm MIR (mid-infrared) luminescence corresponding to the Dy3+: 6H 13/2 →6H 15/2 transition was achieved for the first time in Dy3+/Yb3+ ions co-doped SrF 2 crystals. 2 at% Dy3+: SrF 2 ，2 at% Dy3+/5 at% Yb3+: SrF 2 , and 5 at% Yb3+: SrF 2 crystals were grown by Bridgman method. The influence of Yb3+ on its spectral properties and energy transfer mechanisms has been studied. In comparison to Dy3+ doped SrF 2 crystals, Dy3+/Yb3+ co-doped crystals exhibit not only intense 2.9 µm emission but also longer high laser energy level lifetimes, favoring 2.9 µm population inversion and lasing behavior. Furthermore, the ET efficiency from Yb3+ to Dy3+ in Dy3+/Yb3+ co-doped crystals is found to be as high as 95.34%, indicating that the ET from Yb3+ is efficient. The results show that incorporating Yb3+ into Dy3+: SrF 2 crystals improves the ability to achieve 2.9 µm lasing action, which could be used as a potential gain media for laser diode-pumped MIR lasers. • The Dy3+, Dy3+/Yb3+ and Yb3+ doped SrF 2 single crystals were grown by the Bridgman-Stockbarger method. • Intense 2.9 µm mid-infrared emission is observed in Dy3+/Yb3+: SrF 2 crystal under 975 nm excitation. • Detailed spectroscopic properties and energy transfer mechanisms were studied. • Dy3+/ Yb3+: SrF 2 crystals are expected to achieve mid-infrared laser output. [ABSTRACT FROM AUTHOR]

The polarized absorption, emission spectra and decay time measurements of Pr-doped CaYAlO single crystal have been performed at room temperature. Based on the Judd-Ofelt theory, the spectroscopic parameters $$\Upomega_{t} (t = 2,4,6)$$ , radiative transition probabilities, radiative lifetimes and branching ratios were obtained. The stimulated emission cross-section, fluorescence lifetimes and the quantum efficiency of the promising laser transition were also calculated and compared with other reported crystals. The results show that Pr:CaYAlO is a promising candidate for visible solid-state laser emission. [ABSTRACT FROM AUTHOR]

Abstract: The Sm3+:Sr3Gd(BO3)3 single crystal with dimensions of Φ20×25mm3 was grown by the Czochralski method in nitrogen atmosphere. The effective segregation coefficient of Sm3+ was measured as 0.975. The polarized absorption spectra, emission spectra and fluorescence decay curves of the crystal were measured. Based on the Judd–Ofelt theory, spectroscopic parameters of the crystal, including the oscillator intensity parameters Ω t (t=2, 4, 6), spontaneous emission probabilities, fluorescence branching ratios, and radiative lifetimes were calculated and analyzed. The crystal exhibited a broad absorption band from 390nm to 418nm, a broad emission band from 585nm to 625nm, as well as a fluorescence lifetime up to 2.04ms. These results indicate Sm3+:Sr3Gd(BO3)3 crystal is promising for lasing in visible region. [Copyright &y& Elsevier]

Highlights: [•] Yb3+:LaCa4O(BO3)3 single crystal was grown with high concentration doping. [•] Laser potentiality was evaluated based on the spectral and laser parameters. [•] Continuous wave laser operation was realized. [•] An output power of 0.77W and a slope efficiency of 15.71% at 1077nm were obtained. [•] The spectra and laser properties of Yb3+:LaCa4O(BO3)3 crystal were firstly reported. [Copyright &y& Elsevier]

Dy3+-actived Gd 0.1 Y 0·9 AlO 3 (abbr. as Dy: GdYAP) crystal was grown successfully by using Czocharlski (CZ) method and yellow emission performances were characterized to study the influence of Gd3+ ions on the absorption or emission spectra, which are non-optically active in the visible and infrared ranges. Minor changes have been observed in the absorption peaks of the crystal near 450 nm but the yellow emission peaks are still located near 572 nm. The largest emission cross-section σ em was obtained to be 5.62 × 10−21 cm2 (E//b) and the fluorescence lifetime τ r (Dy3+: 4F 9/2) of Dy: GdYAP crystal was fitted to be 0.316 ms. As compared with 2 at.% Dy: YAP crystal, the lifetimes τ r of the lower energy level (Dy3+: 6H 13/2) has decreased in the Dy: GdYAP crystal. Particularly, the yellow emission has enhanced greatly in Dy: GdYAP crystal excited by 275 nm through the sensitization of Dy3+ by Gd3+, making it potential to realize yellow lasers with available UV pump source. The mixed crystal doped with rare-earth ions provide more options for exploring different laser characteristics and more flexible pump sources. • The single crystal of Dy: GdYAP were grown by Czocharlski (CZ) method. • The yellow fluorescence properties of the Dy: GdYAP mixed crystal under the pumping of 450 nm were studied specifically. • The energy transfer mechanism from Gd3+ to Dy3+ in Dy: GdYAP crystal was discussed. [ABSTRACT FROM AUTHOR]

A series of high-quality Dy3+-doped (Lu x Y 1- x) 3 Al 5 O 12 (x = 0, 1/3, 1/2, 2/3, abbr. as Dy3+: LuYAG) crystals have been grown by the Czochralski method, namely Dy3+: Y 3 Al 5 O 12 , Dy3+: LuY 2 Al 5 O 12 , Dy3+: Lu 1.5 Y 1.5 Al 5 O 12 , and Dy3+: Lu 2 YAl 5 O 12 crystals with similar Dy3+ concentration of 4 at%. Such crystals were investigated and compared through the measurements of their mechanical and spectral characteristics like absorption, emission spectra, and fluorescence decay times. The crystal crack and inclusion problems were discussed and various precautions were taken to improve the crystalline quality. In all Dy3+: LuYAG crystals, absorption cross-section of each absorption band increases with an increment of Lu3+ content, and the strong absorption with a peak at 447 nm makes Dy3+: LuYAG as highly effective to be pumped by blue-emitting LDs (laser diodes). Under 447 nm excitation, strong yellow emissions (582 nm) were obtained, and in four samples Dy3+: Lu 1.5 Y 1.5 Al 5 O 12 crystal shows an intense intensity in the yellow region. Decay times of Dy3+: 4F 9/2 level increases with an increment of Lu3+ content. Comparison of mechanical and spectroscopic features revealed that the best candidate for achieving yellow lasing action was Dy3+: Lu 1.5 Y 1.5 Al 5 O 12 crystal. [Display omitted] • High-quality Dy3+-doped (Lu x Y 1- x) 3 Al 5 O 12 (x = 0, 1/3, 1/2, 2/3) crystals were grown. • Structural, mechanical, and spectroscopic features were characterized and analyzed. • Segregation coefficients of Dy3+ ion decrease with the increment of Lu3+ ions' concentration. • Lu3+ ions contribute to yellow emissions enhancement and extend Dy3+: 4F 9/2 level decay time. • Dy: LuY 2 Al 5 O 12 crystal exhibits the optimal mechanical strength among all studied crystals. [ABSTRACT FROM AUTHOR]

In this work, we report the enhanced 2080 nm emission from Ho3+ and 1999 nm emission of Tm3+ both via Er3+ sensitization in Gd 3 Ga 5 O 12 (abbr. as GGG) crystals excited with 965 nm laser diode (LD) respectively. The underlying mechanisms were analyzed based on the measurements of absorption and emission spectra as well as fluorescence decay curves. Optical parameters including absorption and emission cross-sections, as well as fluorescence decay times are evaluated and compared. Owing to the co-doped sensitizer ion Er3+, a strong absorption near 965 nm plays an important role in the enhanced 2080 nm emission by transferring pump energy to Ho3+: 5I 7 level in Er, Ho: GGG crystal, similarly, transferring energy from Er3+ to Tm3+: 3F 4 level is conducive to improve 1999 nm emission in Er, Tm: GGG crystal. The above results demonstrate that the introduction of Er3+ into Ho3+ or Tm3+ activated materials offers a promising approach to obtain an enhanced 1.9–2.1 μm laser, which could operate upon 965 nm LD pumping, and the efficient energy transfer plays a key role in rare-earth ions doped luminescent materials. [Display omitted] • Er3+/Ho3+ and Er3+/Tm3+ codoped GGG single crystals were grown. • Optical absorption and infrared emissions including decay time measurements were investigated. • Er3+ improves 1.9–2.1 μm emissions in Er,Ho:GGG and Er,Tm:GGG crystals. • The energy transfer mechanism between Er3+ and Ho3+/Tm3+ was discussed. • Er,Ho:GGG and Er,Tm:GGG crystals are promising for laser gain materials. [ABSTRACT FROM AUTHOR]

1 at% Dy3+: CaF 2 and 1 at% Dy3+/5 at% Y3+: CaF 2 crystals were grown by Bridgman method. Absorptions, visible and mid-infrared emissions, and fluorescence decay curves were measured. By applying Judd-Ofelt (J-O) theory, for Dy3+/Y3+: CaF 2 crystal stronger oscillator strength and radiation transition probability were derived. The effect of Y3+ ions incorporation into CaF 2 crystals on the light emission of Dy3+ ions was discussed. Co-doped Y3+ ions can destroy Dy clusters, cripple the concentration quenching effect, and enhance the yellow and mid-infrared fluorescence intensity. The yellow fluorescence intensity of Dy3+/Y3+: CaF 2 is ~ 70 times higher than that of Dy3+: CaF 2 crystal. The local structure of Dy3+ ions was analyzed, and co-doping Y3+ can increase the quantity of tetragonal Dy clusters. In Dy3+/Y3+: CaF 2 crystal, the tetragonal Dy clusters occupy the dominant position, and the fluorescence lifetime (τ f) is relatively short. It can be concluded that Dy3+: CaF 2 and Dy3+/Y3+: CaF 2 crystals are expected to achieve yellow and mid-infrared laser output simultaneously. • The Dy3+ and Dy3+/Y3+ doped CaF 2 single crystals were grown by the Bridgman-Stockbarger method. • Visible light and mid-infrared spectra properties were studied in detail. • The influence of co-doped Y3+ ions on the local geometric structure and spectral properties of Dy3+ ions were discussed. • Dy3+: CaF 2 and Dy3+/Y3+: CaF 2 crystals are expected to achieve yellow and mid-infrared laser output simultaneously. [ABSTRACT FROM AUTHOR]

In this exploration, the 2 at% Dy3+ and 3 at% Y3+ codoped LaF 3 single crystal was grown by the temperature gradient technique. The influence of non-optically-active Y3+ ions on the luminescence of Dy3+ ions in LaF 3 crystals has been explored. Geometry optimization demonstrates that the crystallographic symmetry for Dy3+ ions can be distorted from C 2 to lower symmetry C 1. Low temperature excitation and emission spectra prove that Dy3+ ions occupy the same kind of spectroscopic site in Dy3+/Y3+ codoped LaF 3 crystals. The Judd-Ofelt (J-O) theory analysis and room temperature fluorescence emission spectra have testified that the fluorescence emission intensity of Dy3+ with Y3+ is several times than that without Y3+ in LaF 3 at yellow and mid-infrared region. Codoping with non-optically-active Y3+ ions could weaken the concentration quenching effect of Dy3+ and strengthen the luminescence intensity of Dy3+ ions. • The 2 at% Dy3+ and 3 at% Y3+ codoped LaF 3 single crystal was grown by the temperature gradient technique. • Low temperature excitation and emission spectra prove that Dy3+ ions occupy the same kind of spectroscopic site in Dy3+/Y3+ codoped LaF 3 crystals. • The Judd-Ofelt theory analysis and room temperature fluorescence emission spectra have testified that the fluorescence emission intensity of Dy3+ with Y3+ is several times than that without Y3+ in LaF 3 at yellow and mid-infrared region. • The net gain cross-section spectra show that the tunable laser can be obtained at the range of 2930-3200 nm, when the population inversion p is greater than 0.4. [ABSTRACT FROM AUTHOR]