A series of Gd3+ doped in 0, 0.5 mol%, and 1.0 mol% tetragonal LiYF4: Dy3+/Eu3+ transparent bulk single crystals with a I4(1)/a space group in size of similar to & Oslash;10 & times; 30 mm were grown by Bridgman method. The impacts of Gd3+ ion incorporating on the structure and yellow emission of the crystals were systematically investigated. X-ray patterns (XRD) show that the LiYF4 single crystals still maintain the crystal structure when the doping amount of Gd3+ reaches 1.0 mol%. However, the main diffraction peaks shift towards small angles. Rietveld refinement analysis further confirmed that Gd3+ ions replace Y3+ lattices sites. Under the excitation of 453 nm light, the yellow emission at 575 nm was observed. When the doping amount of Gd3+ attained 0.5 mol%, the yellow emission reached the strongest, and then with the further enhancement of Gd3+ ion content to 1 mol%, the fluorescence intensity began to decrease. The incorporation of the Gd3+ ions will cause the lattice distortion of LiYF4 and change the local field environment of the Dy3+ and Eu3+ luminescent ions, which ultimately enhances the yellow fluorescence emission. Excessive Gd3+ ion doping increases the interionic distance between Eu(3+)and Dy(3+)ions, and reduces the energy transfer efficiency, leading to a diminution in yellow light intensity. The results show that Dy3+/Eu3+/Gd3+ co-incorporated LiYF4 single crystal is a promising material for the purpose of yellow laser output.

Mode-locked lasers operating in the 2 μm region are of great value for various spectroscopic applications and investigations of laser-matter interactions. However, ultrafast lasers that exhibit both a short pulse duration and a wide emission spectrum below 1.9 μm remain challenging. In this work, a passively mode-locked Tm:CaF2 laser was demonstrated at approximately 1886.2 nm with a pulse duration of 3.7 ps and a maximum average output power of 171 mW, by using Gires-Tournois interferometer mirrors for intracavity dispersion compensation. In contrast, the introduction of Gd3+ co-doping enabled the first realization of a mode-locked Tm,Gd:CaF2 laser, which generated significantly shorter pulses of 1.7 ps. Moreover, the Tm,Gd:CaF2 laser exhibited a broadened tuning range of 142.2 nm compared to 127.6 nm obtained in the Tm:CaF2 laser. These results confirm that co-doping Gd3+ ions enhances the performance of Tm-based CaF2 lasers, making Tm,Gd:CaF2 crystals a promising gain medium for a broadband mode-locked laser around 1.9 μm.

Objective Nd-doped alkaline-earth fluoride laser crystals (Nd, R:MF2, M=Ca, Sr; R=La, Ce, Gd, Y, Lu, Sc) exhibit broad emission bandwidths, long fluorescence lifetimes, and high thermal conductivity, making them promising candidates for high-repetition-rate ultrafast lasers. However, the complex correlation among crystal composition, local structure, and spectroscopic properties lacks quantitative modeling, and trial-and-error methods still dominate material screening processes. This study constructs a predictive model that directly correlates crystal composition with photoluminescence parameters, thereby providing a theoretical tool for the rational design and optimization of novel Nd-doped fluoride laser materials. Methods A dataset of approximately 110 reported photoluminescence parameters, including the absorption cross section (ACS at 796 nm), peak emission cross section (PECS for the F-4(3/2)-> I-4(11/2) transition), emission bandwidth (EB for the F-4(3/2)-> I-4(11/2) transition), fluorescence quantum efficiency (FQE), fluorescence branching ratio (FBR for the F-4(3/2)->(4)I(11/2 )transition), and fluorescence lifetime (FL of the F-4(3/2) energy level), is compiled for Nd, R:CaF2 and Nd, R:SrF2 crystals. The input features include Nd and R ion fractions, as well as the host matrix type (CaF2 or SrF2). Following statistical correlation analysis, all features are standardized and transformed whenever necessary to enhance linear learnability. A multilayer feedforward back-propagation (BP) neural network is then constructed with two hidden layers containing 64 and 32 neurons using ReLU activation; the model is trained with the Adam optimizer adopting mean squared error as the loss function, while overfitting is mitigated through cross-validation and early stopping strategies. Model performance is evaluated using the coefficient of determination (R-2 ) and mean absolute error (MAE) between predicted and experimental values. Results and Discussions The trained model accurately reproduces the experimental parameters, achieving R(2 )values of 0.97 (PECS), 0.83 (ACS), 0.84 (FBR), 0.86 (FQE), 0.90 (EB), and 0.84 (FL), respectively. This demonstrates that the spectroscopic performance of Nd-doped fluoride crystals can be reliably predicted using only compositional information. Feature importance contribution analysis shows that all input parameters contribute comparably to most outputs; the host matrix dominates the determination of emission bandwidth with a contribution of approximately 0.30, while the influence of Y ion fraction remains relatively low at around 0.09. The predictive capability is further validated by exploring Nd, Y:SrF2 compositions with the Nd ion fraction ranging from 0.05% to 1% and Y ion fraction from 0.5% to 10 %. The model predicts that the peak emission cross section increases as the Nd ion fraction decreases and Y ion fraction rises, reaching a maximum of approximately 6.3 & times;10(-20) cm(2) at 0.05 % Nd ion fraction and 10 % Y ion fraction. The fluorescence lifetime increases with decreasing Nd ion fraction up to roughly 380 mu s, whereas its dependence on Y exhibits a non-monotonic trend due to the competition between local symmetry effect and concentration-induced cross relaxation. The predicted emission bandwidth exceeds 28 nm at high Nd ion fractions and low Y ion fractions, satisfying the broad bandwidth requirements for ultrafast laser operation. Experimental measurements on synthesized Nd, Y:SrF2 crystals (0.6 %- 0.8% Nd ion fraction, 1 % -9 % Y ion fraction) verify the predicted trends, especially the monotonic decrease in fluorescence lifetime as the Y ion fraction increases from 1 %to 4 %. In addition, predictions for Nd, Y:CaF2 and Nd, Gd:CaF2 crystals show similar compositional dependencies yet distinct quantitative differences. For Nd, Y:CaF2, the emission cross section reaches 4.6 & times;10(-20)cm(2), the lifetime extends to approximately 450 mu s at low Nd ion fractions, and the maximum emission bandwidth exceeds 32 nm. For Nd, Gd:CaF2, lifetime up to 650 mu s is predicted at low Nd and high Gd ion fractions, while the emission cross section saturates at around 2.8 & times;10(-20) cm(2). These systematic predictions highlight the capability of the model to reveal composition-dependent trends and identify optimal doping regimes for different spectroscopic performance targets. Conclusions A feed-forward BP neural network model is successfully established to quantitatively correlate the compositions of Nd, R:CaF2 and Nd, R:SrF2 crystals with their spectroscopic parameters. The model achieves high prediction accuracy (R-2 >= 0.83 for all outputs) and reveals clear trends regarding how dopant ion fraction and host matrix govern absorption and emission cross sections, fluorescence lifetime, quantum efficiencies, branching ratios, and emission bandwidths. Importantly, the model is experimentally validated on Nd, Y:SrF2 crystals, confirming its predictive reliability. This work demonstrates for the first time that the spectroscopic performance of Nd-doped fluoride crystals can be directly predicted from compositional information without requiring explicit structural or spectroscopic input data. The proposed approach not only accelerates the screening of laser gain materials but also provides a generalizable framework for the rational design of advanced crystals intended for ultrafast laser applications.

High-quality Ho3+: LiYbF4 single crystals with Ho3+ concentrations from 0 to 3.0 mol% in size of centimeter level were successfully grown using the Bridgman method. In the self-activated system, Yb3+ ions are intrinsic constituents of the LiYbF4 host lattice and simultaneously act as sensitizer ions, enabling strong absorption of 980 nm pump radiation and efficient energy transfer to Ho3+ ions. The structural and spectroscopic properties of the crystals were systematically investigated as a function of Ho3+ concentration. Under 980 nm excitation, intense mid-infrared emission centered at 2.9 & micro;m corresponding to the Ho3+:5I6 -> 5I7 transition was observed, with the maximum intensity obtained at a Ho3+ concentration of 2.0 mol%. The emission cross-section at 2.9 & micro;m was calculated using the F & uuml;chtbauer-Ladenburg method based on the measured fluorescence spectra and Judd-Ofelt analysis, yielding a maximum value of 2.90 & times; 10-20 cm2. Decay curve fitting using an Inokuti-Hirayama expression indicates dipole-dipole energy transfer from Yb3+ to Ho3+, which is in agreement with the expected cross-relaxation scheme. The efficient energy transfer from Yb3+:2F5/2 to Ho3+:5I6 with an efficiency of 73.9% can be reached inferred from the measurements of lifetimes. The concentration-dependent emission behavior, lifetime analysis, and population inversion characteristics indicate that an optimal balance between energy transfer and cross-relaxation processes occurs at 2.0 mol% Ho3+ doping. These results demonstrate that self-activated Ho3+: LiYbF4 crystals are promising gain media for diode-pumped mid-infrared lasers near 2.9 & micro;m.

Bensity of 3.085 cm. The site concentrations of Yb and Er are determined as 7.63 * 10 <^> 20 atoms-em 165 * 10 <^> 18 atoms-cm(3), respectively. The refractive index follows the Sellmier Fitting Formula of n(2)-1 (1-0.0693712) + 0.06937542/(42-1.0926222) + 0.9091323/(1-0.0693752) at the wavelength ange of 200-1000 nm. The absorption coefficient and absorption cross-section at the wavelength of 976 nm are respectively. The emission cross-section and fluorescence lifetime at 1550 mm 1.95c * m <^> - 2 * an * 8g * 0.92 * 10 <^> - 20 * c * m <^> 2 ,,, are , respectively. The pump saturation intensity (Jar) and the minimum pum ntensity (mm) Kinder the excitation wavelength of 976 nm are 1.89 kW-cm2 and 0.015 kW-em, respectively

Lanthanide-doped ultrasmall upconversion nanocrystals exhibit unique optical properties that differ significantly from bulk materials, making them highly promising for diverse applications. However, their widespread applications have long been impeded by extremely weak photoluminescence due to severe surface quenching effect. Herein, we present a Li+-doping-induced phase engineering strategy to achieve significantly enhanced upconversion luminescence in ultrasmall Cs2ZrF6:Yb/Er nanocrystals (NCs). While initial Li+ doping improves crystallinity, yielding up to a 63-fold emission increase, further doping triggers a phase transition to form heterophase nanocrystals consisting of trigonal Cs2ZrF6 and tetragonal LiYbF4. The synergistic effect of improved crystallinity and reduced local symmetry around lanthanide ions results in a 302-fold boost in emission intensity, even as the particle size decreases to similar to 6.1 nm. Moreover, these ultrasmall nanocrystals display anomalous anti-thermal quenching behavior, with luminescence intensity increasing as temperature rises from 303 to 483 K, driven by defect-mediated energy repopulation. This work not only offers a robust approach for fabricating ultrasmall, high-brightness NCs but also establishes phase engineering as a pivotal mechanism for modulating local crystal field, paving the way for high-performance, thermally stable ratiometric nanothermometry.

A series of fluoroxide glasses with the compositions of 63SiO(2)-10H(3)BO(3)-15Na(2)CO(3)-4KF-7CeF(3)-alpha EuF3 (alpha = 0-7.0 mol%) were synthesized via melt-quenching. Transparent glass-ceramics (GCs) containing NaCeF4:Eu3+ self-luminous nanoparticles (similar to 62 nm) were obtained after crystallization at 620 degrees C. X-ray powder diffraction analysis revealed that when the Eu3+ doping concentration was below 7 mol%, the precipitated crystalline phase consisted exclusively of NaCeF4. However, at a Eu3+ concentration of 7 mol%, a secondary phase of NaEuF4 began to co-precipitate alongside NaCeF4. Under 350 nm excitation, the precursor glass exhibits blue emission from Ce3+ (5d -> 4f) and red emission from Eu3+ (D-5(0)-> F-7(2)). Furthermore, as the concentration of Eu3+ doping increases, the blue emission intensity of Ce3+ gradually weakens, while the ones of Eu3+ gradually strengthen. It leads to a transition from blue to red emission in the GC, thereby achieving tunable color emission. The energy transfer mechanism between Ce3+ as a sensitizer ion and Eu3+ was investigated. The maximum fluorescence lifetime of Ce3+ ions in the GCs was determined to be similar to 26.76 ns, which is a significant decrease compared to the fluorescence lifetime of Ce3+-doped LiYF4 (11.28 ms), mainly due to the cross-relaxation effect of Ce3+ ions. We explored the potential application of the GCs in highly sensitive temperature sensors. Temperature-dependent spectra revealed a linear relationship between the fluorescence intensity ratio (blue/red) of Ce3+ and Eu3+ in the range of 298 similar to 423 K. At 298 K, the maximum absolute sensitivity (S-a) and relative sensitivity (Sr) of the Eu3+-Ce3+ (I-410 nm/I-613 nm) non-thermally coupled levels reached 1.198 % K-1 and 1.130 % K-1, respectively, surpassing most reported materials. Additionally, the temperature resolution of the Eu3+-Ce3+ (I-410 nm/I-613 nm) is 0.025 K, indicating excellent temperature discrimination of the sample. These results indicate that Eu3+-doped NaCeF4 GCs exhibit outstanding potential for optical thermometry due to their high sensitivity, superior material stability, and excellent luminescent properties.

Understanding the magnon dynamics near the rare-earth ion ordering temperature is crucial for revealing the complex exchange interactions between R3+ and Fe3+ ions in RFeO3 (where R is a rare-earth element). With Ho3+ substitution, Gd0.3Ho0.7FeO3 undergoes a Gamma(4)-Gamma(2) spin reorientation transition in the range 48-34 K, which induces complex magnetic competition between the Fe3+ and R3+ sublattices. Here, we employ low-temperature terahertz time-domain spectroscopy under magnetic field to investigate the magnetic field-dependent spin dynamics of Gd0.3Ho0.7FeO3 single crystals. At 2-6 K, with the magnetic field applied along the c-axis, two magnon resonance peaks are observed, which split between 1 and 6 T, merge at 7 T, and re-split at 8 T. This anomalous behavior, which distinctively differs from the simple monotonic splitting in typical canted antiferromagnets, is attributed to the strong Gd3+-Fe3+ antiferromagnetic coupling that drives the reversal of Fe3+ magnetic moments at a critical field. These results provide in-depth insight into the intricate R3+-Fe3+ coupling in orthoferrite antiferromagnets and offer potential avenues for manipulating magnons excitations.

We report on continuous-wave and passively mode-locked operation of a diode-pumped Yb:Ca3TaGa3Si2O14 laser. In the continuous-wave regime, the laser delivered a maximum output power of 408 mW at 1045.5 nm, corresponding to a slope efficiency of 58.1% and a laser efficiency of 53.4%. By incorporating a quartz-based Lyot filter, a continuous wavelength tuning range of 82 nm, spanning from 1007 to 1089 nm, was achieved. In the mode-locked regime, a commercial semiconductor saturable absorber mirror was employed to initiate and sustain soliton-like pulse shaping, and pulses as short as 50 fs were generated at a central wavelength of 1052.4 nm, with an average output power of 40 mW at a pulse repetition rate of 73.9 MHz. To the best of our knowledge, this is the first demonstration of a mode-locked laser based on the Yb:Ca3TaGa3Si2O14 langasite-type non-centrosymmetric crystal, highlighting its significant potential as a gain medium for sub-100 fs solid-state lasers.

This work demonstrates continuous-wave (CW) and passively Q-switched (PQS) laser operation in a Tm,Gd:SrF2 single crystal under laser diode (LD) pumping. For an output coupler (OC) transmission of T = 5 %, the CW laser delivers a maximum average output power of 2.89 W, corresponding to a slope efficiency of 83.1 % and a photon quantum efficiency of 200 %. The high photon quantum efficiency results from the intrinsic cross-relaxation (CR) process of Tm3+ ions, and the clustering of ions in the Tm,Gd:SrF2 single crystal further promotes this process. For an OC transmission of T = 5 %, the PQS laser achieves a maximum average output power of 311 mW, with a minimum pulse duration of 27.20 ns at a repetition rate of 5.05 kHz, corresponding to a single-pulse energy of 61.60 μJ and a peak power of 2.26 kW. These results indicate that Tm,Gd:SrF2 single crystal is a promising gain medium for highly efficient ∼ 2 μm lasers and short-pulse laser generation.

We report on an Yb:YAB laser pumped by a spatially single-mode, low-power, fiber-coupled InGaAs laser diode at 976 nm, delivering soliton pulses as short as 36 fs at 1059.7 nm via soft-aperture Kerr-lens mode-locking. The average output power amounts to 156 mW at a pulse repetition rate of ∼66.7 MHz. To the best of our knowledge, this represents the first demonstration of Kerr-lens mode-locked operation with the Yb:YAB crystal, and the shortest pulses ever achieved from an Yb:YAB laser.

In this study, Ca2+ modified Ni2+: LiBaF3 single crystals were grown by the Bridgman method to investigate the influence of inert ion incorporation on the crystal structure and NIR-II luminescence properties. X-ray diffraction and Rietveld refinement support that Ca2+ ions preferentially substitute for Ba2+ ions in the LiBaF3 lattice, inducing lattice contraction and local structural modification without changing the cubic phase. Under 393 nm excitation, the Ca2+ doped Ni2+: LiBaF3 crystals exhibit a broad NIR-II emission band centered at approximately 1430 nm, originating from the3T2g(F)→3A2g(F) transition of Ni2+ ions. The emission intensity is closely related to the concentration of Ca2+ ions. When the nominal concentration of Ca2+ ions is 0.4 mol%, the emission intensity is approximately 1.5 times higher compared to the crystal without Ca2+ incorporation. Meanwhile, Ca2+ incorporation effectively broadens the emission bandwidth, increasing the FWHM from 256.14 to 278.33 nm, which is larger than that of the corresponding Mg2+ ions modified sample. Furthermore, temperature-dependent measurements reveal improved thermal stability after Ca2+ incorporation, with 59.4 % of the room temperature emission intensity retained at 473 K. The results demonstrate that Ca2+ incorporation is an effective strategy to regulate the local environment of Ni2+ ions and achieve broadband, thermally stable NIR-II emission in LiBaF3 single crystals.

At 2-6 K, with the magnetic field along the c-axis, two magnon resonance peaks are observed Gd 0.3 Ho 0.7 FeO 3 crystals, which is attributed to the strong Gd 3+ -Fe 3+ antiferromagnetic coupling that drives the reversal of Fe 3+ magnetic moments.

Nd,Y:CaF2 (NYCF) crystals are exceptional gain materials for high-power laser drivers; however, laser-induced damage remains a substantial challenge that restricts their broader application. In this study, by establishing an in situ testing system for photothermal weak absorption and the laser-induced damage threshold (LIDT), the relationship between the photothermal weak absorption characteristics of NYCF and its LIDTs was analyzed. A fully connected neural network was employed to facilitate deep learning of these relationships, thereby enabling non-destructive evaluation of NYCF via photothermal weak absorption. Moreover, this study examined both the effect of spot size during testing and the influence of crystal orientation on the evaluation outcomes. The underlying mechanisms were further elucidated by investigating NYCF's thermal mechanical properties and damage characteristics. This work not only offers a rapid, non-destructive method for evaluating the laser damage resistance of NYCF using artificial intelligence but also enhances the understanding of its damage mechanisms.

The mechanistic origins underlying the anisotropic brittleness and incipient plasticity of fluorite-structured alkaline earth fluorides (MF2, M = Ca, Sr, Ba) are revealed by a unified first-principles framework. Our computations revealed that the notorious {111} cleavage propensity originates from an exceptionally low tensile strength, a critically limited strain threshold governed by the onset of phonon instability, and the minimum cleavage energy among low-index planes. In contrast, incipient plastic flow is dominated by slip along the <110>{001} system, which possesses not only the lowest shear strength but also, decisively, the lowest generalized stacking fault energy (GSFE) barrier, a feature enabled by significant anionic relaxation. The competition between these deformation modes is rigorously quantified by the ratio of the cleavage energy to the slip energy barrier E-C/Gamma. The resulting E-C/Gamma landscape exhibits profound anisotropy. A near-unity ratio (similar to 1.0) on {110} and {111} planes signifies virtually identical energetic costs for cleavage and slip nucleation, thereby rationalizing the extreme brittleness. Conversely, the conspicuously high E-C/Gamma ratio (>3.8) on {001} planes affirms that dislocation-mediated plasticity is energetically strongly favored over fracture, consistent with experimental evidence. We reveal that this fundamental deformation anisotropy stems from the pronounced directionality of M-F bonds coupled with intense electrostatic repulsion between like-charged ions during shear, which collectively dictate a unique energetic landscape. This work establishes the E-C/Gamma criterion as a predictive framework, providing a fundamental basis for understanding deformation mode selection in fluorite-structured crystals and directly bridging atomic-scale bonding to macroscopic mechanical response.

The degradation of calcium fluoride (CaF2) crystals in deep ultraviolet (DUV) lithography systems poses a critical challenge to the safe and stable operation of such systems. Understanding the degradation dynamics and underlying physical mechanisms induced by high-energy photon irradiation is essential for improving the radiation resistance of CaF2 crystals. This work proposes a rapid assessment method for evaluating the radiation-resistant lifetime of CaF2 crystals based on X-ray exposure. By characterizing the dynamic degradation behavior of CaF2 crystals under various X-ray doses and integrating multidimensional defect characterization techniques, the physical mechanism of X-ray-induced degradation was systematically elucidated, with dislocation density identified as the dominant factor governing the radiation resistance of CaF2 crystals. This study not only elucidates the dynamic evolution and critical factors of degradation processes in CaF2 crystals under X-ray irradiation but also lays a solid foundation for the future optimization of their radiation-resistant properties in high-energy radiation environments.

We report on the passively mode-locked operation of an Yb:SrF 2 laser generating sub-40 fs pulses at ∼1 μm. By using a high-brightness Yb-fiber laser as the pump source, the Yb:SrF 2 laser delivered soliton pulses as short as 37 fs at 1066.4 nm via soft-aperture Kerr-lens mode-locking, with an average output power of 85 mW at a pulse repetition rate of ∼71.8 MHz. To the best of our knowledge, this is the first demonstration of Kerr-lens mode-locking using the Yb:SrF 2 crystal.

We report on continuous-wave and passively mode-locked operation of a diode-pumped Yb:Ca 3 TaGa 3 Si 2 O 14 laser. In the continuous-wave regime, the laser delivered a maximum output power of 408 mW at 1045.5 nm, corresponding to a slope efficiency of 58.1% and a laser efficiency of 53.4%. By incorporating a quartz-based Lyot filter, a continuous wavelength tuning range of 82 nm, spanning from 1007 to 1089 nm, was achieved. In the mode-locked regime, a commercial semiconductor saturable absorber mirror was employed to initiate and sustain soliton-like pulse shaping, and pulses as short as 50 fs were generated at a central wavelength of 1052.4 nm, with an average output power of 40 mW at a pulse repetition rate of 73.9 MHz. To the best of our knowledge, this is the first demonstration of a mode-locked laser based on the Yb:Ca 3 TaGa 3 Si 2 O 14 langasite-type non-centrosymmetric crystal, highlighting its significant potential as a gain medium for sub-100 fs solid-state lasers.

Power scaling of a continuous-wave (CW) bulk laser in the mid-infrared (Mid-IR) spectral region has been demonstrated employing a 2.5 at.% Er:CaF2 crystal slab with double-end-pumping configuration and tailored pump beam profile for better geometry matching. A maximum output power of 22.5 W is achieved at 2.8 μm, corresponding to a slope efficiency of 29.4%. The M2 -factor is 1.27 in the y-direction, compared to 10.29 in the x-direction. To the best of our knowledge, this presents the record power for end-pumped solid-state CW lasers in the 3-μm spectral range at room temperature. This work indicates that Er:CaF2 crystals with a low doping level are promising candidates for high-power laser emission in the Mid-IR region.