Search

In this work, four Pr

The spectroscopic properties of a series of Dy3+ single-doped and Dy3+/Nd3+, Dy3+/Tb3+, and Dy3+/Tm3+ co-doped YAlO3 (yttrium aluminum perovskite, YAP) phosphors were investigated and compared through the measurements of optical absorption, emission spectra, and fluorescence decay curves. For the Dy3+ ion single-doped samples, the intensity of each absorption band increases with an increment in Dy3+ ion doping concentration, and the identified strong absorption peak at 447 nm indicates that Dy3+:YAP phosphors are suitable to be pumped by a blue laser diode (LD). For all co-doped samples, absorption peaks of Dy3+ ion along with some of the absorption bands of Nd3+, Tb3+, and Tm3+ ions are observed. Under 351 and 447 nm excitation, a prominent emission peak at 572 nm was obtained in all the samples, corresponding to Dy3+: 4F9/2 → 6H13/2 transition. Here, 2 at% Dy3+:YAP phosphor exhibits the highest yellow emission intensity under 447 nm pumping. Among the three kinds of Dy3+ co-doped phosphors, Dy3+/Tb3+:YAP phosphor possesses the dominant yellow emission. The fluorescence decay curves show exponential behaviour and are fitted well. The Commission International de L'Eclairage (CIE) chromaticity coordinates were calculated following the respective emission spectra, and it is found that all the coordinates locate in the yellow region. The energy transfer (ET) processes were investigated and the concentration quenching mechanism was discussed. The obtained results suggest that Dy3+-activated YAP phosphors are good candidates for yellow LED applications.

Intense 2.9 µm emission corresponding to Dy3+:6H13/2 → 6H15/2 transition was achieved in Yb3+/Dy3+ codoped CaYAlO4 crystal for the first time. The effects of Yb3+ on the spectroscopic properties and energy transfer mechanisms were investigated. In comparison with Dy3+ singly-doped CaYAlO4 crystal, Yb3+/Dy3+ codoped crystal not only has intense 2.9 µm emission, but also has longer upper laser level lifetime, which facilitates particle number inversion and laser behavior in 2.9 µm. Furthermore, the energy transfer efficiency from Yb3+ to Dy3+ in Yb3+/Dy3+ codoped crystal was as high as 87.3%, indicating effective energy transfer of Yb3+. Besides, the energy transfer microscopic parameters between Yb3+ and Dy3+ were theoretically analyzed. The results indicate that the introduction of Yb3+ is very beneficial for achieving 2.9 µm laser in Dy3+: CaYAlO4 crystal, which could act as a potential gain media for LD pumped mid-infrared laser.

A series of Dy3+-activated CaYAl3O7 (Dy: CaYAl3O7) phosphors were synthesized by the solid-state reaction at high temperature. The prepared phosphors were characterized by X-ray diffraction, and the results showed that the main phase of the phosphor was CaYAl3O7. The structure of CaYAl3O7 was investigated and the first-principles calculations were carried out for the first time. The photoluminescence properties of them were investigated in detail through the measurements of their emission spectra and fluorescence decay curves. The fluorescence decay curves of the 4F9/2 state with different Dy3+ ions concentrations exhibited multi-exponential decaying behavior, then the lifetimes were fitted and compared. Furthermore, the energy transfer processes within Dy: CaYAl3O7 phosphors were investigated. In the visible region, a strong emission band was observed with peak at 574 nm, corresponding to 4F9/2 → 6H13/2 transition, which indicates that Dy: CaYAl3O7 is good material for yellow light applications.

The Er3+/Yb3+, Er3+/Nd3+ and Er3+/Dy3+ co-doped BaLaGa3O7 crystals were grown by the Czochralski method. The absorption spectra, up-conversion emission spectra, near-infrared and mid-infrared emission spectra, as well as the fluorescence decay curves of them were measured at room temperature. Detailed spectroscopic analyses were carried out and the spectral parameters of them were compared. Furthermore, the energy transfer processes among Er3+-Yb3+, Er3+-Nd3+ and Er3+-Dy3+ were investigated and the rate-equation theory models were built and discussed. The results demonstrate that Er/Nd: BaLaGa3O7 crystal is a best candidate for obtainment of ~2.7 µm laser among the three doping kinds, since the introduction of Nd3+ not only increases the absorption efficiency of pump energy, but also inhibits the self-termination bottleneck effect, which are both beneficial to the output of the mid-infrared ~2.7 µm laser.

The spectroscopic characteristics of a series of Dy3+/Tm3+-codoped LaF3 single crystals have been studied for mid-IR emissions through Dy3+:6H13/2 → 6H15/2 transition. Optimal mid-IR emission was achieved in 3 at% Tm3+ and 2 at% Dy3+ co-doped LaF3 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 LaF3 single crystal can be a potential medium for mid-IR lasers.

In this paper, a series of Dy3+/Gd3+ codoped LaF3 (LDG) single crystals were grown by the Bridgman–Stockbarger method. The influence of non-optically-active Gd3+ ions on the luminescence of Dy3+ ions in LaF3 crystals has been explored. Dy3+/Gd3+ ions substitute for the La lattice in LaF3, and the local site symmetry of each subset of Dy3+ will be distorted from C2 to lower symmetry C1. Based on the measured low temperature excitation and emission spectra, it can be proved that Dy3+ ions occupy the same kind of spectroscopic site in Dy3+/Gd3+ codoped LaF3 crystals, and codoped Gd3+ ions do not change the spectroscopic site symmetry of Dy3+. When Gd3+ ions were codoped into the Dy3+:LaF3 crystal, Dy–Gd clusters were formed around single Dy3+ ions to isolate Dy3+ ions from each other and weakened the concentration quenching effect of Dy3+ ions. When 2 at% Dy3+ and 1 at% Gd3+ ions were doped into the LaF3 crystal, the strongest yellow luminescence was obtained under excitation at 349 nm and 453.75 nm, respectively. While doped with 2 at% Dy3+ and 2 at% Gd3+ ions, the LDG crystal exhibited the strongest mid-infrared fluorescence emission intensity. This concludes that the LDG crystals are suitable for achieving a yellow laser (4F9/2 → 6H13/2 transition) pumped using a InGaN blue laser diode (LD) and a mid-infrared laser (6H13/2 → 6H15/2 transition) pumped using a 1280 nm LD.

Dy3+-actived Gd0.1Y0·9AlO3 (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 σem was obtained to be 5.62 × 10−21 cm2 (E//b) and the fluorescence lifetime τr (Dy3+: 4F9/2) of Dy: GdYAP crystal was fitted to be 0.316 ms. As compared with 2 at.% Dy: YAP crystal, the lifetimes τr of the lower energy level (Dy3+: 6H13/2) 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.

A series of high-quality Dy3+-doped (LuxY1-x)3Al5O12 (x = 0, 1/3, 1/2, 2/3, abbr. as Dy3+: LuYAG) crystals have been grown by the Czochralski method, namely Dy3+: Y3Al5O12, Dy3+: LuY2Al5O12, Dy3+: Lu1.5Y1.5Al5O12, and Dy3+: Lu2YAl5O12 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+: Lu1.5Y1.5Al5O12 crystal shows an intense intensity in the yellow region. Decay times of Dy3+: 4F9/2 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+: Lu1.5Y1.5Al5O12 crystal.

Er,Eu:YAlO3 (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 4I13/2 and 4I11/2 levels, large absorption cross-section at 974 nm and 790 nm, and large stimulated emission cross-section at 2704 nm. The co-dopant Eu3+ decreases the fluorescence lifetime of 4I11/2 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 Er3+-Eu3+ 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-p2, 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.

Single crystals of pure and Er 3+ doped BaLaGa 3 O 7 were grown successfully by the Czochralski technique. The absorption spectra, emission spectra including up-conversion, near-infrared and mid-infrared fluorescence spectra, as well as the fluorescence decay curves were measured at room temperature. The optical parameters of absorption and emission cross sections, the fluorescence lifetimes were evaluated and compared. Based on the Judde-Ofelt theory, Judde-Ofelt parameters such as the fluorescent branching ratios, the spontaneous transition probabilities and the radiative lifetimes were calculated. According to the energy transfer diagram, the rate equation model was built and discussed. In summary, Er 3+ : BaLaGa 3 O 7 crystal is attractive and significant as laser gain material for realization of ∼2.7 μm laser output.

Enhanced 2.86 µm emission corresponding to Ho3+: 5I6→5I7 was achieved in Nd3+/Ho3+ codoped CaLaGa3O7 crystal for the first time. The detailed spectroscopic properties and energy transfer mechanism of the as-grown crystal were investigated. The results show that the Nd3+ ion is not only a very good sensitizer in a Ho3+ doped CaLaGa3O7 crystal, but also an appropriate deactivated ion with efficient depopulation of the Ho3+: 5I7 level for enhancing the 2.86 µm fluorescence emission. And the energy transfer efficiency of Ho3+: 5I7→Nd3+: 4I13/2 is estimated to be 93%, which indicates that the self-termination effect for the 2.86 µm holmium laser is suppressed successfully in Nd3+/Ho3+: CaLaGa3O7 crystal. Besides, the thermal properties of Nd3+: CaLaGa3O7 crystal were also studied. In conclusion, the introduction of Nd3+ is favorable for achieving an enhanced 2.86 µm emission in Nd3+/Ho3+: CaLaGa3O7 crystal, which can act as a new promising candidate for mid-infrared lasers.

Dy3+ doped and Dy3+/Nd3+ codoped LaF3 single crystals were successfully grown by the Bridgman-Stockbarger method in a self-made medium frequency furnace. The crystal structures of LaF3 were investigated, and their geometry optimizations were carried out. The electronic structures including band structure and density of state were calculated by using first-principles calculations based on density functional theory. The polarized absorption and emission spectra including near-infrared and mid-infrared fluorescence spectra were measured at room temperature. The energy transfer mechanism from Nd3+ ion to Dy3+ ion was presented, and the microscopic transfer parameters were calculated based on the phonon-assisted energy transfer theory. In summary, two promising routes of Dy3+/LaF3 crystal pumped by 1280 nm LD and Dy3+/Nd3+/LaF3 crystal pumped by 790 nm LD were proposed for a mid-infrared laser.

Yb/Ho: CaLaGa3O7 as mid-IR laser crystal was successfully grown by the Czochralski method for the first time. The effects of Yb3+ on the structure parameters and spectroscopic properties have been investigated. In comparison with Ho3+ singly-doped CaLaGa3O7 crystal, Yb3+ not only enhances 2.86 µm emission but also depopulates the Ho3+: 5I7 level in Yb/Ho: CaLaGa3O7 crystal, which is beneficial to the possible population inversion for Ho3+: 5I6→5I7. Results indicate that the prepared Yb/Ho: CaLaGa3O7 crystal is a promising candidate for 2.86 μm mid-infrared laser applications.

Nd3+ was introduced into Er3+: CaLaGa3O7 crystal for an enhanced ~2.7 µm emission. The structure parameters of Er: CaLaGa3O7 and Nd,Er: CaLaGa3O7 crystals are determined by the X-ray Rietveld refinement method. The effects of Nd3+ on the spectroscopic properties and mutual energy transfer mechanisms were investigated. It is found that Nd3+ greatly improves the absorption pump efficiency and thus enhances the Er3+ ~ 2.7 µm emission by nearly 5 times, meanwhile, quenches the ~ 1.5 µm near-infrared emission. Therefore, the self-termination effect for ~ 2.7 µm erbium laser is suppressed successfully. Furthermore, the energy transfer efficiencies of Nd3+→Er3+ and Er3+→Nd3+ are estimated to be 92.3% and close to 100%, respectively. Besides, the radiative transfer microscopic parameters between Nd3+ and Er3+ were theoretically analyzed. The results indicate that the introduction of Nd3+ is very beneficial in achieving ~ 2.7 µm laser in Er3+: CaLaGa3O7 crystal, which could act as a potential gain media for LD pumped MIR laser.

A new rare-earth borate Er6B4O15was synthesized by a solid-state reaction technique. The crystal was obtained by a flux method. Single-crystal X-ray diffraction analysis revealed that the crystal structure is composed of ErO6polyhedra sharing edges and BO3groups. The absorption, near-infrared fluorescence spectra and the fluorescence decay curve of Er:4I13/2energy level in the Er6B4O15crystal were measured at room temperature. The absorption peak was located at 977 nm with absorption cross section of 1.16 × 10−21 cm2and a full width at half-maximum (FWHM) of 16 nm, which is very suitable for commercial 980 nm laser diode pumping. A maximum emission peak at 1560 mm with a broad FWHM of 64 nm was observed in this crystal because of the Er3+transition4I13/2→4I15/2, while the emission cross section was calculated to be 8.53 × 10−20 cm2. These results imply that the Er6B4O15crystal is a promising candidate material for the achievement of an eye-safe near-infrared wavelength laser.

Growth of Tm, Ho singly-doped and Tm/Ho co-doped CaLaGa3O7 crystals by Czochralski method are investigated for the first time. The polarized absorption spectra, fluorescence spectra and luminescence decay curves of Tm: CaLaGa3O7, Ho: CaLaGa3O7 and Tm/Ho: CaLaGa3O7 crystals are reported. Based on the Judd–Ofelt theory and the polarized absorption spectra, the spontaneous transition probabilities, the fluorescent branching ratios and the radiative lifetimes were calculated. The crystals exhibit a broad emission band at about 2.0 μm, corresponding to 3F4→3H6 of Tm3+ and 5I7→5I8 of Ho3+, respectively. The energy transfer parameters in Tm/Ho: CaLaGa3O7 crystal between Tm3+ and Ho3+ are theoretically analyzed. These results show that Tm: CaLaGa3O7, Ho: CaLaGa3O7 and Tm/Ho: CaLaGa3O7 crystals are excellent potential tunable laser media for the ∼2.0 μm regions.

In this work, we report the enhanced 2080 nm emission from Ho3+ and 1999 nm emission of Tm3+ both via Er3+ sensitization in Gd3Ga5O12 (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+: 5I7 level in Er, Ho: GGG crystal, similarly, transferring energy from Er3+ to Tm3+: 3F4 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.

We firstly report the passively Q-switched solid state laser based on the Sb 2 Te 3 saturable absorber, as far as we know. The Sb 2 Te 3 nanosheets are prepared via a facile hydrothermal reaction method. The pulsed laser is centered at 1045.2 nm with the single pulse energy up to 0.917 μJ. Its maximum output power is 81 mW. The corresponding pulse width and repetition frequency rate are 678 ns and 88.34 kHz, respectively. These results suggest that the Sb 2 Te 3 nanosheets prepared via a facile hydrothermal reaction method possess the great potential for near infrared passively Q-switched solid state laser.

The synthesis and optical characterizations of CaLaGa 3 O 7 crystals with different Er dopant concentration are reported. The optical parameters related to absorption and emission cross-sections were evaluated and compared. It was found that the NIR fluorescence weakens, at the same time Mid-IR fluorescence intensity strengthens with the increment of Er 3+ ion dopant concentration in Er: CaLaGa 3 O 7 crystals. Furthermore, the energy transfer mechanism in Er: CaLaGa 3 O 7 crystal was studied in this work. Besides, the radiative transfer microscopic parameters of 4 I 11/2 and 4 I 13/2 levels were theoretically analyzed. Hence, these results indicate that 30 at% Er 3+ doped CaLaGa 3 O 7 crystal has potential applications in 2.7 μm laser.

Yb 3+ and Er 3+ co-doped SrLaGa 3 O 7 (abbr. as Yb,Er: SLGO) bulk crystal with dimensions of Φ 20×30 mm was grown successfully by the Czochralski (Cz) method. The absorption and fluorescence spectra as well as the fluorescence decay curves of Yb,Er: SLGO crystal were measured and investigated. The emission cross-section and fluorescence lifetimes have been obtained at the ~2.7 µm wavelength. Based on Yb 3+ -Er 3+ energy level diagrams, the rate equation model was built and discussed. It is found that 2.7–3.0 µm emission has been improved in Yb,Er: SLGO crystal under excitation of 980 nm, owing to the sensitization of the co-dopant Yb 3+ and the resonant energy transfer from Yb 3+ to Er 3+ . A noteworthy result is that Yb,Er: SLGO crystal is an excellent mid-infrared laser gain material.

Single crystals of pure and Er 3+ doped CaLaGa 3 O 7 were firstly grown by the Czochralski technology. The structure of CaLaGa 3 O 7 was investigated. The electronic structures of CaLaGa 3 O 7 crystal were performed by using first-principles calculations based on density functional theory (DFT) methods. Its band structure and density of states were presented. The polarized absorption, emission spectra including up-conversion, near-infrared and mid-infrared fluorescence spectra, as well as the fluorescence decay curves of Er: CaLaGa 3 O 7 crystal were measured at room temperature. Detailed spectroscopic analyses of Er: CaLaGa 3 O 7 were carried out. Based on the Judd–Ofelt theory and the polarized absorption spectra, the spontaneous transition probabilities, the fluorescent branching ratios and the radiative lifetimes were calculated. The energy transfer mechanism in Er: CaLaGa 3 O 7 crystal was also studied in this work. It concludes that Er: CaLaGa 3 O 7 crystal can act as a promising candidate for mid-infrared lasers.

We demonstrate for the first time, to our certain knowledge, a dual-wavelength passively Q-switched bulk laser based on the MoS2/graphene heterojunction saturable absorber. This heterojunction is prepared though a facile hydrothermal reaction and shows an excellent saturable absorption charateristic with the modulation depth of 9.12%. A 370 ns pulse laser with single pulse energy of 0.734 μJ is achieved. The corresponding output power and repetition frequency rate are 102 mW and 138.9 kHz, respectively. The stable pulse laser operates at 1047.2 and 1049.6 nm, simultaneously. This work validates the MoS2/graphene heterojunction is a promising saturable absorber for multiwavelength near-infrared pulse lasers and it may broaden the range to choose optical modulator.

The bulk crystal of 5at% Yb 3+ , 20 at% Er 3+ and 0.2 at% Pr 3+ triply doped SrLaGa 3 O 7 (abbr. as Yb,Er,Pr:SLGO) was grown by the Czochralski method. The effects of co-dopant Yb 3+ and Pr 3+ on the spectroscopic properties and the mutual energy transfer mechanism were investigated, via the measurements of its absorption, near-infrared and mid-infrared fluorescence spectra, as well as the fluorescence decay curves of Er 3+ : 4 I 13/2 and 4 I 11/2 levels at room temperature. As compared with 20at% Er 3+ singly doped SrLaGa 3 O 7 crystal, ~2.7 µm emission intensity corresponding to Er 3+ : 4 I 11/2 → 4 I 13/2 transition is enhanced greatly in the Yb,Er,Pr:SLGO crystal. Spectral analyses indicate that the sensitization of Yb 3+ to Er 3+ improves the ~2.7 µm emission in Yb,Er,Pr:SLGO crystal, meanwhile, the depopulation of Pr 3+ from Er 3+ decreases the ~1.5 µm emission and inhibits the self-termination effect. The energy transfer efficiencies of Yb 3+ →Er 3+ (ET1), Er 3+ →Pr 3+ (ET2) and Er 3+ →Pr 3+ (ET3) were estimated and discussed. The above results conclude that Yb,Er,Pr:SLGO crystal is a good candidate for LD pumped mid-infrared laser.

A series of Dy3+-doped LaMgAl11O19 (Dy: LMA) phosphors were prepared by the solid state reaction method. The band structure and density of states of LaMgAl11O19 were calculated. The crystalline structures were investigated by X-ray diffraction and transmission electron microscopy. The chemical elements of Dy: LMA phosphors were characterized by energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. All the Dy: LMA phosphors exhibit intense yellow emissions at 573 nm under the excitation of 449 nm. Based on the measured absorption, emission spectra and the fluorescence decay curves, as well as the discussion and comparison of their spectral parameters, the optimal doping concentration of Dy3+ in LMA is confirmed to be 4 at.%. The Commission International del’Eclairage (CIE) 1931 chromaticity coordinates of all the samples were located in the yellow region. The mechanism of concentration quenching of Dy3+ in LMA was discussed.

Mixed crystals of Dy3+/Sr2+: LaF3 and Dy3+/Ca2+: LaF3 were grown by Bridgman technique and their spectral properties were investigated. Spectra broadening and peak shifts were observed, indicating the co-doping of Sr2+/Ca2+ brings about a more disordered local symmetry of Dy3+, which makes both crystals favorable for tunable lasing action. Low-temperature high resolution excitation and emission spectra were carried out for exploring the types of luminescent center of Dy3+ in crystals. Room-temperature absorption and emission spectra, together with the fluorescence decay curves were studied in both crystals for estimating their potentials for yellow and MIR lasers. Under 450 nm excitation, the largest emission cross-sections at 571 nm of 1.51 × 10−21 cm2 for Dy3+/Sr2+: LaF3 crystal and 1.56 × 10−21 cm2 for Dy3+/Ca2+: LaF3 crystal, along with the lifetimes of Dy3+: 4F9/2 level as 0.983 ms for Dy3+/Sr2+: LaF3 crystal, 1.143 ms for Dy3+/Ca2+: LaF3 crystal were obtained, respectively. Besides yellow emissions, MIR emissions approximately at 3 μm are more appealing. Under 1280 nm excitation, the largest emission cross-sections of 0.304 × 10−20 cm2 at 2885 nm in Dy3+/Sr2+: LaF3 crystal, and 0.319 × 10−20 cm2 at 2880 nm in Dy3+/Ca2+: LaF3 crystal, together with rather long lifetimes of Dy3+: 6H13/2 in the level of milliseconds were achieved, making them useful media for MIR lasers.

1 at% Dy3+: CaF2 and 1 at% Dy3+/5 at% Y3+: CaF2 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+: CaF2 crystal stronger oscillator strength and radiation transition probability were derived. The effect of Y3+ ions incorporation into CaF2 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+: CaF2 is ~ 70 times higher than that of Dy3+: CaF2 crystal. The local structure of Dy3+ ions was analyzed, and co-doping Y3+ can increase the quantity of tetragonal Dy clusters. In Dy3+/Y3+: CaF2 crystal, the tetragonal Dy clusters occupy the dominant position, and the fluorescence lifetime (τf) is relatively short. It can be concluded that Dy3+: CaF2 and Dy3+/Y3+: CaF2 crystals are expected to achieve yellow and mid-infrared laser output simultaneously.

Optical features of Dy3+:YAP and Dy3+/Tb3+:YAP single crystals that were successfully fabricated by the Czochralski method were reported. The thermal behaviors and XRD rocking curves of the grown Dy3+:YAP crystal were carried out. The identified broad absorption bands of Dy3+:6H15/2 → 4I15/2 with FWHMs approximately to 11 nm and the moderate absorption cross-sections at 450 nm in both crystals, imply their high suitability to the blue LD pumping. Polarized emission spectra with yellow fluorescence peaks at 572 nm were acquired in both crystals by means of a 450 nm Xenon lamp excitation. As compared with Dy3+:YAP crystal, the larger emission cross-sections of 7.83 × 10−21, 9.08 × 10−21 and 9.01 × 10−21 cm2 for E//a, E//b and E//c polarizations respectively, were determined in Dy3+/Tb3+:YAP crystal. Moreover, a slightly reduced lifetime of the upper laser level 4F9/2 and a much shortened lifetime of the lower laser level 6H13/2 were obtained in Dy3+/Tb3+:YAP crystal, implying the existent energy migration between Dy3+ and Tb3+, as well as an effective deactivation of Tb3+ to Dy3+. The role of Tb3+ to reinforce Dy3+:4F9/2 → 6H13/2 emission in YAP host was established. On the basis of the derived results, both crystals could be recognized as competitive materials for polarized yellow lasers, especially the Dy3+/Tb3+:YAP crystal.

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.

Mid-infrared waveband lasers have demonstrated important applications in the fields of atmosphere pollution monitoring, gas flow monitoring, ocean detection, laser medicine, military confrontation and basic scientific researches etc. In this paper, we review the research development of bulk crystal growth, physicochemical, spectral and laser properties of 2.5–5.0 μm waveband mid-infrared laser crystals in recent years. A serial of gallate and aluminate crystals with low phonon energy were grown by the Czochralski method, such as Er3+ activated and rare earth ions co-doped Gd3Ga5O12(GGG), SrGdGa3O7, SrLaGa3O7, CaYAlO4 and CaGdAlO4 crystals, Ho3+ activated and rare earth ions co-doped GGG crystals, as well as Dy3+:YAlO3 crystals, and 2.5–3.4 μm waveband emissions were obtained in these crystals. High quality Dy3+:KPb2Cl5, Cr2+:CdSe and Cr2+:Fe2+:CdSe crystals were grown by the Bridgman method, and 2.5–5.0 μm waveband emissions were obtained in these crystals. The physicochemical and spectral properties of the above crystals were studied systematically, with focus on analyses of the concentration effect of activated ions Er3+, the sensitization mechanism of the co-dopant sensitized ions and the impact of the depopulated ions on the inhibition of self-termination effect. The fluorescence dynamic of the activated ions within the mid-infrared waveband, the energy transfer efficiencies between activated ions and co-dopant sensitization ions, as well as between the activated ions and co-dopant depopulation ions were calculated, and the energy transfer mechanism was discussed. Based on the results of spectroscopic investigations, the concentrations of Er3+, the types and the concentrations the co-dopant sensitization ions were optimized in different kinds of crystals. The laser properties of Er3+ activated GGG, CaYAlO4 crystals were presented. Finally, 2.7–2.8 µm multi-wavelength CW or pulsed lasers were achieved in Er:GGG, Er,Pr:GGG and Er:GGG/GGG composite crystals end-pumped by 965 nm LD or in Cr,Er:YSGG crystals by Xenon lamp, furthermore, the single longitudinal mode microchip laser was achieved in Er:GGG crystal for the first time.

Yb3+ ion was introduced as a sensitizer for commercial 980 nm pump source utilization in Yb3+/Dy3+ co-doped YAP crystal for the first time. An intense broadband 3 μm emission (Dy3+:6H13/2 → 6H15/2 transition) in Yb3+/Dy3+:YAP crystal was demonstrated. As compared with Dy3+ singly-doped YAP crystal under 802 nm OPO excitation, the larger emission cross-section (=4.25 × 10−21 cm2) and effective emission bandwidth (=316 nm) were obtained in Yb3+/Dy3+:YAP crystal under 979 nm OPO laser excitation, which make it favorable for tunable lasers. The energy transfer efficiency from Yb3+ to Dy3+ was obtained as high as 97.2%. The greatly reduced near-infrared emission of Yb3+:2F5/2 → 2F7/2 transition and largely shortened lifetime of Yb3+:2F5/2, also reveal the efficient energy transfer from Yb3+ to Dy3+. The energy transfer micro-parameters were calculated by spectral overlapping integral method, and the main energy transfer channel is determined. In addition, the energy dispersive X-ray spectroscopy, X-ray diffraction and Raman spectrum were measured in Yb3+/Dy3+:YAP crystal. Rietveld refinement was also employed to investigate the variation in lattice parameters in Yb3+/Dy3+:YAP crystal. It can be concluded that Yb3+/Dy3+:YAP is an excellent candidate for achieving mid-infrared laser.

In this exploration, the 2 at% Dy3+ and 3 at% Y3+ codoped LaF3 single crystal was grown by the temperature gradient technique. The influence of non-optically-active Y3+ ions on the luminescence of Dy3+ ions in LaF3 crystals has been explored. Geometry optimization demonstrates that the crystallographic symmetry for Dy3+ ions can be distorted from C2 to lower symmetry C1. Low temperature excitation and emission spectra prove that Dy3+ ions occupy the same kind of spectroscopic site in Dy3+/Y3+ codoped LaF3 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 LaF3 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.