SrF2 Crystals Research Articles

Enhanced the quantum efficiency of Tm3+ ∼2 μm laser in crystal through an energy transfer process of 3H5 level

The concentration dependence of the fluorescence and lifetime evolutions of states relevant to three near-infrared emission bands were measured and analyzed for Tm:SrF2 crystals. The fast quenching of ∼1.2 μm fluorescence (3H5) was observed as the Tm concentration increased. The cross-relaxation and multi-phonon relaxation processes between Tm3+ ions cannot explain this phenomenon. Through spectral and rate-equation analysis, two possible energy transfer mechanisms, cross-relaxation from the 3H5 level and cooperative energy transfer within Tm3+ clusters, are proposed. And based on the new modified model, the quantum efficiency of the Tm ∼2 μm lasers could surpass the traditional 200% limit. This new energy transfer has the potential for exceptionally high efficiency excitation of Tm-doped laser materials.

Gain performance and thermal effects of Nd:Glass and Nd,Y:SrF2 crystal

The gain performance and thermal effects of Nd:glass (N31) and Nd,Y:SrF2 crystal are investigated and compared. The results show that, under the same pump conditions, Nd,Y:SrF2 can provide a small-signal gain similar to that of N31. The main advantages of Nd,Y:SrF2 are its weaker thermal effects and greater thermal-fracture limitations compared with those of N31. In this paper, the two gain media are compared in the form of rods whose diameter is 5 mm and length is 60 mm. The small-signal gain coefficients of N31 and Nd,Y:SrF2 are 1.39 and 1.46, respectively, at a pump energy of 1.5 J/1 Hz. The pump energy is set at 1.5 J/8 Hz to experimentally investigate their thermal effects. The thermal wavefront of N31 is 0.987λ at a repetition rate of 10 Hz, whereas that of Nd,Y:SrF2 is 0.679λ. In thermal destructive experiments, N31 fractured at an average pump power of 15 W (1.5 J/10 Hz), whereas Nd,Y:SrF2 fractured at a higher power of 27 W (1.5 J/18 Hz) owing to its excellent thermal conductivity, which is 7.28 times that of N31. These results indicate the potential of Nd,Y:SrF2 crystal as a gain medium for high-repetition-rate laser amplifiers.

Effect of strontium fluoride on mechanical and remineralization properties of enamel: An in-vitro study on a modified orthodontic adhesive

ObjectivesEvaluate the ability of strontium fluoride on bond strength and enamel integrity after incorporation within orthodontic adhesive system as a delivery vehicle. MethodsExperimental orthodontic adhesive system Transbond™ XT were modified with 1% Sr2+, 0.5% SrF2, 1% strontium, 0.5% Sr2+, 1% F-, 0.5% F-, and no additions were control. Mixing of formulation was monitored using Fourier transform infrared spectroscopy. Small-molecule drug-discovery suite was used to gain insights into Sr2+, F-, and SrF2 binding. Shear bond testing was performed after 6-months of ageing. Enamel blocks were cut, and STEM pictures were recorded. Specimens were indented to evaluate elastic modulus. Raman microscope was used to collect Raman spectra and inspected using a scanning electron microscope. Crystal structural analysis was performed using X-ray diffraction. Effect of material on cellular proliferation was determined. Confocal was performed to evaluate the effect of formulation on biofilms. ResultsFTIR of modified adhesives depicted peak changes within range due to various functional groups existing within samples. TEM represented structurally optimized hexagonal unit-cell of hydroxyapatite. Mean shear bond strength is recorded highest for Transbond XT with 1% SrF2. Dead bacterial percentage appeared higher in 0.5% SrF2 and 1% F- specimens. Crystal lengths showed an increase in 0.5% and 1% SrF2 specimens. Phase contrast within TEM images showed a union of 0.5% SrF2 crystal with enamel crystal with higher elastic modulus and highly mineralized crystalline hydroxyapatite. Intensity of ν1 PO43- and ν1 CO32- along with carbonate - / ν1PO43- ratio displayed good association with strontium fluoride. The formulation showed acceptable cell biocompatibility (p < 0.353). All specimens displayed characteristic diffraction maxima of different apatite angles within XRD. SignificanceExperimental results suggested good biocompatibility, adequate mechanical strength, and far-ranging crystallization ability. This would provide a new strategy to overcome the two major challenges of fixed orthodontics, biofilm growth, and demineralization of enamel.

Diode-pumped high-peak-power nanosecond Nd,Y: SrF2 regenerative laser amplifier

We demonstrate a regenerative laser amplifier based on laser-diode-pumped Nd, Y:SrF2 crystals with an output of approximately 9.78 mJ/10 Hz. A specially designed birefringent filter was inserted into the cavity to compensate the gain narrowing and amplify the seed pulse with a center wavelength of 1053.3 nm. To optimize the design of the resonator, the thermal wavefront of the laser gain module was simulated and experimentally measured. When a laser pulse with a duration of 9 ns and energy of 1 nJ was injected into the regenerative amplifier, the output energy was 9.78 mJ with peak power of 1.1 MW. The energy stability was 0.72 % RMS. The horizontal and vertical beam quality M2 was 1.18 and 1.23 respectively. The results show the potential of the developed amplifier for application in high-power laser facilities.

Continuous-wave orange laser at 605.98 nm based on a diode-pumped Pr,Gd:SrF2 crystal

Continuous-wave orange laser at 605.98 nm based on a diode-pumped Pr,Gd:SrF2 crystal

Investigation of the photothermal weak absorption and laser damage characteristics of a Nd,Y:SrF2 crystal

The exponential-Chapman quantitative relationship is established between photothermal weak absorption and laser damage characteristics induced by surface defects in Nd,Y:SrF2 crystals.

Effects of temperature on factors relevant to laser operation near 1.6 µm wavelength in resonantly (in-band) pumped CaF2:Er and SrF2:Er crystals: a comparative study

Single crystals of CaF2 and SrF2 containing Er3+ ions with concentrations between 0.01 and 0.6 at% respectively, were grown using the temperature gradient technique (TGT). Absorption spectra related to the 4I15/2 → 4I13/2 transition of Er3+ ions were measured at 5 K to investigate the properties of the crystal field splitting of the 4I13/2 multiplet, and at several temperatures in the region 80 K – 300 K to determine the effect of temperature on the spectral bands. The 4I13/2 → 4I15/2 luminescence spectra were recorded within the same temperature range as for absorption measurement. The analysis of absorption and luminescence spectra provides an in-depth knowledge on the effect of temperature on the factors that govern the efficiency of resonant optical pumping near 1.6 µm and the resulting lasing ability of Er3+ ions imbedded in CaF2 and SrF2 hosts.

Optimizing yellow fluorescence in Dy3+:SrF2 crystal through Gd3+ co-doping

Optimizing yellow fluorescence in Dy3+:SrF2 crystal through Gd3+ co-doping

Visible and mid-infrared spectral features of Dy3+: SrF2 and Dy3+/Y3+: SrF2 crystals

In this work, Dy3+: SrF2 and Dy3+/Y3+: SrF2 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+: SrF2 crystal is higher than that of Dy3+: SrF2 crystal related values. Also, compared to Dy3+: SrF2 crystal, the emission cross-section (3.55 × 10−21 cm2) at 2880 nm and fluorescence decay time (1.062 ms) of Dy3+/Y3+: SrF2 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+: SrF2 and Dy3+/Y3+: SrF2 crystals are potential materials to simultaneously realize yellow and MIR lasing action.

Спектроскопия f-=SUP=-13-=/SUP=--лантаноидов во фторидных кристаллах

The absorption and luminescence spectra of 4f-4f transitions of Yb3+ ions in crystals of CaF2, SrF2, and BaF2 fluorides have been studied. The crystal splitting of the 2F7/2, 2F5/2 levels in Tm2+, Yb3+ by the cubic field decreases linearly with increasing lattice constant. Both lines intersect at the energy of 2F7/2 - 2F5/2 transitions in unperturbed Tm2+, Yb3+ ions. The positions of the f13 levels of Tm2+ or Yb3+ in fluoride crystals are well described by ab-initio relativistic calculations

One- and two-exciton states of pair centers of Kramers Nd3+ions in Nd-doped CaF2 and SrF2 crystals, and their possible use as qubits

Using two-color excitation with narrow laser lines of 0.2 cm−1 and time-resolved site-selective fluorescence spectroscopy, we measured the fluorescence excitation spectra of the one-exciton 4G5/2(1) x 4I9/2(1) state monitored in the near IR, and the two-exciton 4G5/2(1) x 4G5/2(1) state monitored in the near UV of the pair M centers in the Nd3+ doped CaF2 and SrF2 crystals at 6.5 K. We observed the splitting of the one-exciton state of the order of 2–3 cm−1 depending on the type of crystal matrix. A significant inhomogeneous splitting ∼1.5 cm−1 of the spectral lines of the one-exciton state of the pair M centers in the Nd3+: SrF2 crystals was found. The measured single spectral line of the two-exciton state of the pair M centers in these crystals has in one-photon scale the linewidth of ∼0.8 cm−1, which is mainly determined by inhomogeneous broadening.

High-power 2.8 μm lasing in a lightly-doped Er:CaF2 crystal

Er3+-doped crystals pumped by laser diode (LD) is an effective way to obtain near 3 μm laser, which has advantages of low cost and compact structure. CaF2 and SrF2 crystals have the fluorite structure makes Er3+ ions easy to form “clusters”, this effect shortens the space between Er3+ ions, then bring intense interionic energy transfer inside the lightly-doped crystal. Due to the existence of “clusters”, not only the self-termination process was solved, but also the severe thermal damage during the Er3+ 2.8 μm laser generation was avoided. In this work, high quality 1.7 at.% Er:CaF2 laser crystals have been successfully grown by temperature gradient method. LD pumped 2756.6 nm laser with maximum output power of 2.32 W was achieved. It is the highest laser output power generated by LD-pumped Er3+-doped fluoride crystals in recent years. Furthermore, we also demonstrated the 1532 nm LD pumped 1.7 at.% Er:CaF2 laser performance, which proved the strongly energy transfer inside the lightly-doped Er:CaF2 crystal. These results are valuable to the development of the mid-infrared laser towards the direction of compact structure and low cost.

Intense 2.9 µm mid-infrared emission from Dy3+/Yb3+：SrF2 crystal under 975 nm excitation

The intense 2.9 µm MIR (mid-infrared) luminescence corresponding to the Dy 3+ : 6 H 13/2 → 6 H 15/2 transition was achieved for the first time in Dy 3+ /Yb 3+ ions co-doped SrF 2 crystals. 2 at% Dy 3+ : SrF 2 ，2 at% Dy 3+ /5 at% Yb 3+ : SrF 2 , and 5 at% Yb 3+ : SrF 2 crystals were grown by Bridgman method. The influence of Yb 3+ on its spectral properties and energy transfer mechanisms has been studied. In comparison to Dy 3+ doped SrF 2 crystals, Dy 3+ /Yb 3+ 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 Yb 3+ to Dy 3+ in Dy 3+ /Yb 3+ co-doped crystals is found to be as high as 95.34%, indicating that the ET from Yb 3+ is efficient. The results show that incorporating Yb 3+ into Dy 3+ : 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 Dy 3+ , Dy 3+ /Yb 3+ and Yb 3+ doped SrF 2 single crystals were grown by the Bridgman-Stockbarger method. • Intense 2.9 µm mid-infrared emission is observed in Dy 3+ /Yb 3+ : SrF 2 crystal under 975 nm excitation. • Detailed spectroscopic properties and energy transfer mechanisms were studied. • Dy 3+ / Yb 3+ : SrF 2 crystals are expected to achieve mid-infrared laser output.

Er3+ concentration-dependent microstructural and upconversion luminescence process of transparent perfluoride composite glass

Er3+-doped transparent perfluoride composite glass (PFCG) containing SrF2 crystals was obtained by a one-step method. PFCG was observed to maintain the formation of a single SrF2 crystal phase even when the Er3+ doping concentration was as high as 8 mol%. Importantly, Er3+ was enriched in the crystalline region, which promoted grain growth. This ensures effective emission of upconversion (UC). Interestingly, green and red UC emissions were found to be tunable in the range of 1–6 mol% Er3+ doping, and the UC emission and lifetime started to produce concentration quenching until 6 mol% Er3+ doping. To the best of our knowledge, this is the highest quenching concentration of Er3+ in composite-glass materials. Moreover, the dominant UC process was systematically analyzed at different doping levels. This research is expected to provide ideal candidate materials and appropriate Er3+ concentration doping level guidance in PFCG for the field of UC lasers.

Long-wavelength optical properties of the Ca0.33Sr0.33Ba0.33F2 solid solution single crystals

The optical characteristics of Ca0.33Sr0.33Ba0.33F2 (CSBF) single crystal of a ternary solid solution of calcium, strontium and barium fluorides were studied in order to create disordered optical media. Characteristics of the single crystals of individual fluorides CaF2, SrF2, BaF2 and binary solid solutions Ca0.6Sr0.4F2 and Ba0.67Sr0.33F2 were obtained. Broadband reflection and transmission spectra of the said crystals were recorded in the frequency range of 3–5000 cm−1, and the values of the complex refractive indexes and dielectric constants were calculated. The generalized four parameter model were used for calculation of absorption band parameters. For the CSBF crystal, a significant broadening of the band was observed in the absorption region at optical phonon modes along with an increased absorption in the region below the optical phonon frequencies, which is typical for disordered dielectric media.

Tb,Y:SrF2 crystal for efficient laser operation in the visible spectral region.

A Tb,Y:SrF2 crystal with high optical quality is grown using the temperature gradient technique. The spectroscopic and laser properties of the crystal in the visible spectral region are studied. A fluorescence lifetime of 5.6 ms is measured from the crystal, which is beneficial for laser operation with a low threshold. A continuous-wave Tb,Y:SrF2 laser delivers an output power of 259 mW at 545 nm, with a slope efficiency of 35.2%. To the best of the authors' knowledge, this is the first report on a Tb-doped SrF2 laser and represents the highest output power for visible alkaline-earth fluoride lasers. The limitations for power scaling are discussed.

Solid-state laser cooling in Yb:CaF2 and Yb:SrF2 by anti-Stokes fluorescence.

We report on the first example, to the best of our knowledge, of solid-state laser cooling in ytterbium-doped CaF2 and SrF2 crystals by anti-Stokes fluorescence. The crystals were grown by the Czochralski method in a fluorine-rich atmosphere to prevent the formation of divalent ytterbium ions. Using laser-induced thermal modulation spectroscopy (LITMoS), we find the cooling efficiencies for both crystals to be higher than 3% at room temperature. According to model calculations performed using temperature-dependent spectroscopic data, these crystals can be cooled to temperatures as low as 150 K when excited at around 1030 nm.

Growth and mid-infrared emission properties of "mixed" fluorite-type Er:(Ca,Sr)F2 and Er:(Ba,Sr)F2 crystals

Fluorite-type 5 at.% Er3+:(M1,M2)F2 (M1 = Ca, Ba; M2 = Sr) crystals were grown by the conventional Bridgman technique and a comparative study of their spectroscopic properties was performed. The vibronic properties of the fluorite-type crystals were studied by Raman spectroscopy. The Er:(M1,M2)F2 crystals exhibited a slightly inhomogeneous broadening of mid-infrared luminescence spectra as compared to the ‘parent’ compound, Er:SrF2. The luminescence lifetimes of the 4I11/2 and 4I13/2 manifolds were measured, e.g., for the Er:(Ca,Sr)F2 crystal, the luminescence lifetimes were estimated to be 8.64 ms and 5.64 ms, respectively, representing a favorable ratio for mid-IR laser operation.

Clusters modification for tunable photoluminescence in Nd3+:SrF2 crystal

In the work, the first principles calculation and low temperature spectra were utilized to investigate the modification on Nd3+ clusters in SrF2 crystal. The results show that structures of the clusters vary greatly and it depends on the ionic radius of rare-earth La3+, Nd3+, Gd3+ and Y3+. The cubic sublattice centers are stable in large size rare-earth La3+- and Nd3+-doped SrF2, and the square antiprism centers are more stable in smaller size Gd3+- and Y3+-doped crystals. It suggests that the square antiprism clusters become more stable with decreasing ionic radius in going from La3+, Nd3+, Gd3+ to Y3+, while the cubic sublattice centers become unstable. Based on the results, the mixed [Nd3+-La3+] and [Nd3+-Gd3+] clusters are also calculated. Stability of square antiprism clusters is improved with increasing concentration of Gd3+ in [Nd3+-Gd3+] clusters, and that weakened when codoped with La3+. The results reveal that characteristics of the mixed centers depend on species and contents of the ingredient rare-earth ions. Local environment of the active ions could therefore be modified by codoping the other rare-earth ions, which agreed well with the tunable absorption and emission spectra of Nd3+:SrF2 modified by La3+, Gd3+ and Y3+. The varied cluster structures provide us a methodology towards designing of new rare-earth-doped fluoride materials.

Acousto-optic Q-switched Er:CaF2-SrF2 laser at 2.73 μm

A diode-end-pumped Er:CaF2-SrF2 laser actively Q-switched by a TeO2 acousto-optic crystal was demonstrated for the first time, to our best knowledge. By setting the repetition rate of radio frequency signal, 2.73 μm Q-switched lasers with repetition rates of 100–1000 Hz were obtained. With 100 Hz repetition rate, a 390 μJ pulse energy and a 176 ns pulse duration were employed at an absorbed pump power of 2.17 W, and the corresponding peak power was 2.2 kW. These results prove that Er3+-doped CaF2–SrF2 crystal is promising for actively Q-switched laser with high peak power in the mid-infrared region.