CaF2 SrF2 Research Articles

Time‐Resolved Spectroscopy of 4S3/2 Energy State in Er3+‐Doped Fluoroaluminate Glass in a Wide Temperature Range

The development and characterization of some optical properties of erbium Er3+‐doped 98(MgF2–CaF2–SrF2–BaF2–YF3–AlF3)–2(Ba(PO3)2) glass are reported. Luminescence peaks with maxima at 522, 545, 665, and 852 nm are observed upon excitation at a wavelength of 487 nm. The nature of the radiation transitions is explained on the basis of the energy diagram of erbium ions. For the most intense transition 4 S 3/2→4 I 15/2, the lifetime dependence of the 4 S 3/2 state is determined in the temperature range of 90–503 K. The experimental dependence is analyzed using the Riseberg–Moos multiphonon relaxation model. It is shown that the main reason for the decrease in the lifetime is temperature quenching of luminescence caused by a decrease in the effective energy gap ΔE (2 H 11/2–4 S 3/2). The temperature range of applicability of the theoretical Reisberg–Moose model for the 4 S 3/2 →4 I 15/2 transition is determined.

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.

Chemical in‐depth analysis of (Ca/Sr)F2 core–shell like nanoparticles by X‐ray photoelectron spectroscopy with tunable excitation energy

The fluorolytic sol–gel synthesis is applied with the intention to obtain two different types of core–shell nanoparticles, namely, SrF2–CaF2 and CaF2–SrF2. In two separate fluorination steps for core and shell formation, the corresponding metal lactates are reacted with anhydrous HF in ethylene glycol. Scanning transmission electron microscopy (STEM) and dynamic light scattering (DLS) confirm the formation of particles with mean dimensions between 6.4 and 11.5 nm. The overall chemical composition of the particles during the different reaction steps is monitored by quantitative Al Kα excitation X‐ray photoelectron spectroscopy (XPS). Here, the formation of stoichiometric metal fluorides (MF2) is confirmed, both for the core and the final core–shell particles. Furthermore, an in‐depth analysis by synchrotron radiation XPS (SR‐XPS) with tunable excitation energy is performed to confirm the core–shell character of the nanoparticles. Additionally, Ca2p/Sr3d XPS intensity ratio in‐depth profiles are simulated using the software Simulation of Electron Spectra for Surface Analysis (SESSA). In principle, core–shell like particle morphologies are formed but without a sharp interface between calcium and strontium containing phases. Surprisingly, the in‐depth chemical distribution of the two types of nanoparticles is equal within the error of the experiment. Both comprise a SrF2‐rich core domain and CaF2‐rich shell domain with an intermixing zone between them. Consequently, the internal morphology of the final nanoparticles seems to be independent from the synthesis chronology.

Thermophysical Properties of Single Crystals of CaF2–SrF2–RF3 (R = Ho, Pr) Fluorite Solid Solutions

Single crystals of Ca1 – ySryRхF2 + х (R = Ho, Pr) solid solutions with high optical quality have been grown by the Bridgman technique in vacuum using a fluorination atmosphere. The thermal conductivity of the Ca0.60Sr0.40 – хHoхF2 + х solid solutions decreases from 3.27 to 2.37 W/(m K) as the fraction of holmium rises from 0 to 3 mol %, respectively. The room-temperature thermal conductivity of the Ca0.50Sr0.50 – хPrхF2 + х solid solutions decreases from 3.38 to 2.18 W/(m K) as the fraction of praseodymium rises from 0 to 8 mol %, respectively. Increasing the holmium and praseodymium content of the ternary solid solutions leads to a gradual increase in their refractive index. With increasing wavelength, the refractive index gradually decreases.

Study of Yb3+ Optical Centers in Fluoride Solid Solution Crystals CaF2–SrF2–YbF3

A concentration series of Ca(1 − X)SrXF2:4 mol % YbF3 crystals with Х varying from 0 to 1 has been grown. The absorption spectra of Yb3+ ions in these crystals are measured at temperatures of 300 and 77 K. It is shown that the intensity ratio of the absorption lines of clusters and tetragonal centers in the congruent crystals is higher than that in the other CaF2–SrF2 solid solution crystals. Analysis of the absorption profiles of Yb3+ optical centers in the concentration series of the solid solution crystals shows that it is energetically favorable for the Sr2+ ion to enter the local environment of both the tetragonal center and the cluster.

Spectroscopic and laser properties of a broadly tunable diode-pumped Tm3+ :CaF2–SrF2 laser

The spectroscopic and laser properties of mixed fluoride Tm:CaF2–SrF2 crystals were investigated. The 1.9 m radiation was obtained in two samples with Tm3+ ion doping concentrations of 1.0 mol% and 2.0 mol% under laser diode pumping at 763 nm. The highest slope efficiency of 32.5% and the widest laser tuning range of 232 nm (1761–1993 nm) were demonstrated with the 1%-doped sample. The maximal output power amplitude of 3.4 W at 1902 nm for an absorbed pump power amplitude of 13.8 W was demonstrated with the 2%-doped sample.

Growth and Some Physical Properties of Congruently Melting Fluorite Solid Solutions Crystals in the CaF2–SrF2–RF3 (R = La, Ce) Systems

Congruently melting Ca0.77Sr0.07La0.16F2.16 and Ca0.70Sr0.11Ce0.19F2.19 fluorite solid solutions crystals in the CaF2–SrF2–RF3 (R = La, Ce) systems have been grown from melt by the Bridgman technique in a fluorinating atmosphere. Their optical, mechanical, electrophysical, and thermophysical characteristics have been studied. The crystals are transparent in a wide spectral range; their refractive indices are nD = 1.468 (R = La) and 1.479 (R = Ce), and their microhardness (НV ∼ 5.0 GPa) and ionic conductivity (σ ∼ 3 × 10–3 S/cm at 823 K) exceed significantly the corresponding values for CaF2 and SrF2 crystals. The materials under study are promising isomorphic-capacious crystalline matrices for various applications in photonics and solid-state ionics.

Mid-infrared Er:CaF2–SrF2 bulk laser Q-switched by MXene Ti3C2Tx absorber

We report a diode-pumped passively Q-switched Er:CaF2–SrF2 laser at 2.73 μm with MXene Ti3C2Tx as a saturable absorber (SA). A maximum average output power of the pulsed laser was measured at 286 mW, with a shortest duration of 814 ns and a repetition rate of 45.3 kHz. The corresponding single-pulse energy and peak power were calculated to be 6.32 μJ and 7.76 W, respectively. The results suggest the promising potential of MXene as an efficient SA for short pulse lasers in the mid-infrared spectral band.

Rare-earth doped fluoride phosphate glasses: structural foundations of their luminescence properties.

We report a detailed structural investigation of a series of fluoride-phosphate glasses with different phosphate/fluoride ratios in the system xSr(PO3)2-(100 - x)[AlF3-CaF2-SrF2-MgF2] with x = 5, 10, 20, 40. Raman and multinuclear solid NMR spectroscopies confirm that the polyphosphate network structure is successively transformed to a structure dominated by Al-O-P linkages with increasing AlF3 content. Average numbers of Al-O-P linkages have been quantified by 27Al/31P NMR double-resonance techniques. The majority of the fluoride species are found in an alkaline earth metal/aluminum rich environment. The local environments for rare-earth ions have been characterized by EPR spectroscopy of Yb3+ ion spin probes and by photoluminescence experiments on Eu3+ dopant ions, including the 5D0 → 7F2 and 5D0 → 7F1 transition intensity ratio, the normalized phonon sideband intensities in the excitation spectra, and the lifetime of the 5D0 excited state. The results indicate clear correlations between these parameters as a function of composition, and confirm that even at the highest fluoride levels, there is still some residual rare-earth phosphate coordination.

Fabrication and optical characterizations of CaF2–SrF2–NdF3 transparent ceramic

Nanopowders of CaF2–SrF2–NdF3 were synthesized by direct precipitation method. X-ray powder diffraction and transmission electron microscopy observations indicated that the powders were single phased with mean particle size around 20nm. CaF2–SrF2–NdF3 transparent ceramic was fabricated by hot-pressed (HP) method at the temperature of 800°C under pressure of 30MPa. Micrograph of the transparent ceramic exhibited a pore-free structure and the average grain size was about 0.5μm. For a 2mm thickness ceramic sample, the in-line transmittance of the ceramic sample reached 86% in the wavelength from 250nm to 1400nm. The absorption and emission spectra of transparent ceramics sample were measured and discussed.

The influence of TeO2 on thermal stability and 1.53 μm spectroscopic properties in Er3+ doped oxyfluorite glasses

In this work, the thermal and spectroscopic properties of Er3+-doped oxyfluorite glass based on AMCSBYT (AlF3–MgF2–CaF2–SrF2–BaF2–YF3–TeO2) system for different TeO2 concentrations from 6 to 21mol% is reported. After adding a suitable content of TeO2, the thermal ability of glass improves significantly whose ΔT and S can reach to 118°C and 4.47, respectively. The stimulated emission cross-section reaches to 7.80×10−21cm2 and the fluorescence lifetime is 12.18ms. At the same time, the bandwidth characteristics reach to 46.41×10−21cm2nm and the gain performance is 63.73×10−21cm2ms. These results show that the optical performances of this oxyfluorite glass are very well. Hence, AMCSBYT glass with superior performances might be a useful material for applications in optical amplifier around 1.53μm.

Laser performance of diode-pumped Nd, Y-codoped CaF 2–SrF 2 mixed crystal

A disordered Nd, Y-codoped CaF2–SrF2 mixed crystal was obtained by the temperature gradient technique (TGT). The absorption and fluorescence spectra of the crystal were measured at room temperature. Diode-pumped continuous-wave (CW) and Q-switched laser operations were demonstrated at 1056 nm with a 0.65 at.% Nd, 10 at.% Y-codoped crystal, for the first time to our knowledge. The CW output power of 724 mW was obtained in a compact linear cavity. Also the Q-switched pulse characteristics of Nd, Y:CaF2–SrF2 laser crystal were reported based on Cr4+:YAG saturable absorbers in a folded cavity. The shortest pulse width of 110 ns and the highest peak power of 383 W were obtained when the initial transmission of the Cr4+:YAG crystals was 90%. The dependence of the operational parameters on the pump power was also investigated experimentally.

Characteristics of a diode-pumped Yb:CaF2–SrF2 mode-locked laser using a carbon nanotube absorber

Yb:CaF2–SrF2 disordered crystals are successfully grown by the TGT method. By using a double-walled carbon nanotube saturable absorber (DWCNT-SA), the continuous-wave mode-locked (CWML) laser properties of Yb:CaF2–SrF2 crystals are demonstrated under diode pumping for the first time. The mode-locked laser delivers pulses as short as 5 ps at a center wavelength of 1045.5 nm without any dispersion compensation. The oscillator operating at a repetition rate of ∼87 MHz delivers 292 mW average output power.

Efficient lasing in diode-pumped Yb3+:CaF2–SrF2 solid-solution single crystals

Single crystals of solid solutions of a high optical quality are grown in the concentration vicinity of the saddle point of the ternary CaF2–SrF2–YbF3 system. Efficient lasing with a small Stokes shift (at 1025 nm) was obtained in 980-nm diode-pumped single crystals. The total lasing efficiency (with respect to the absorbed average pump power) was 59% and the slope efficiency was 83%.

Study of Cohesion, Harmonic and Anharmonic Elastic Properties of CaF2—SrF2 Mixed Crystals

AbstractCohesive and harmonic and anharmonic elastic properties are investigated of CaF2—SrF2 mixed crystals using a three‐body interaction potential which consists of the long‐range Coulomb and three‐body interactions and short‐range van der Waals‐attraction and overlap repulsion, effective upto the second neighbour ions. This two parameter model potential successfully predicts the cohesive energy, the higher order elastic constants, and the pressure derivatives of the second order elastic constants of CaF2—SrF2 mixed crystals.