Search Results (25)

This study evaluates the predictive performance of advanced machine learning models, including DeepBoost, XGBoost, CatBoost, RF, and MLP, in estimating the Ω₂, Ω₄, and Ω₆ parameters based on a comprehensive set of input variables. Among the models, DeepBoost consistently demonstrated the best performance across the training and testing phases. For the Ω₂ prediction, DeepBoost achieved an R² of 0.974 and accuracy of 99.895% in the training phase, with corresponding values of 0.971 and 99.902% in the testing phase. In comparison, XGBoost ranked second with an R² of 0.929 and accuracy of 99.870% during testing. For Ω₄, DeepBoost achieved a training phase R² of 0.955 and accuracy of 99.846%, while the testing phase results included an R² of 0.945 and accuracy of 99.951%. Similar trends were observed for Ω₆, where DeepBoost obtained near-perfect training phase results (R² = 0.997, accuracy = 99.968%) and testing phase performance (R² = 0.994, accuracy = 99.946%). These findings are further supported by violin plots and correlation analyses, underscoring DeepBoost’s superior predictive reliability and generalization capabilities. This work highlights the importance of model selection in predictive tasks and demonstrates the potential of machine learning for capturing complex relationships in data. Full article

Exploring the intrinsic mechanisms of rare-earth ions entering the crystal phase has great significance for finely tuning the luminescent properties of glass–ceramics. Using Er³⁺ ions as a probe, X-ray diffraction was employed to precisely measure the crystallinity of SiO₂-PbF₂-Er₂O₃ glass–ceramics synthesized under various heat treatment conditions, confirming the occurrence of a rapid crystallization process. Additionally, by combining Judd–Ofelt theory with comprehensive analyses of absorption and fluorescence spectra, we calculated the relative proportions of Er³⁺ ions present in the crystal phase. We found that the crystallization process in the glass–ceramics and the incorporation of Er³⁺ ions into the crystal phase did not occur synchronously. This discovery provides new theoretical foundations and practical guidance for understanding the mechanism of rare-earth ion incorporation into crystal phases, which is significant for the development of functional materials with specific luminescent properties. Full article

A disordered Nd:SrLaGaO₄ (Nd:SLG) laser crystal was successfully grown via the Czochralski (CZ) technique. The crystal structure, refractive index, polarized absorption spectra, and stimulated emission spectra were measured. The spectroscopic properties were studied intensively with the Judd–Ofelt (J-O) theory. The maximum absorption cross sections of π- and σ-polarization at 806 nm were calculated to be 3.73 × 10⁻²⁰ and 4.05 × 10⁻²⁰ cm², corresponding to FWHMs of 6.00 and 6.10 nm, respectively. The maximum emission cross sections of π- and σ-polarization at 1076 nm were 3.97 × 10⁻²⁰ and 4.12 × 10⁻²⁰ cm², with FWHMs of 30.21 and 19.44 nm, respectively. The decay life of the Nd³⁺:⁴F_3/2 energy level was fitted to be 0.152 ms, and the fluorescence quantum efficiency was 72.72%. The inhomogeneous broadening in spectra benefiting from the disordered structure indicates the Nd:SLG crystal is a promising gain medium for ultrafast laser and tunable laser generations in the near infrared region. Full article

In the present work, the influence of alkali ions (Li, Na, K) on the structural and spectroscopic properties of silica glasses doped with Sm³⁺ was investigated. Infrared and Raman spectroscopy techniques were used to investigate the structural properties of the alkali silicate glasses. The optical absorption showed bands characteristic of Sm³⁺ ions in alkali silicate glasses, and this was investigated. The Judd–Ofelt theory was applied to evaluate the phenomenological intensity parameters (Ω₂, Ω₄, and Ω₆) of the optical absorption measurements. The multi-channel visible and near infrared emission transitions originating from the ⁴G_5/2-emitting state of the Sm³⁺ in alkali silicate glasses with a maximum phonon energy of ~1050 cm⁻¹ were investigated. From the evaluated Judd–Ofelt parameters, radiative parameters such as spontaneous emission probabilities, radiative lifetimes, branching ratios, and stimulated emission cross-sections were calculated. The recorded luminescence spectra regions revealed intense green, orange, red, and near-infrared emission bands, providing new traces for developing tunable laser and optoelectronic devices. Full article

Six new complexes of the ligand HQ^cy (-4-(cyclohexanecarbonyl)-5-methyl-2-phenyl-2,4-dihydro-3H-pyrazol-3-one) and Ln³⁺ ions with emission in the near-infrared (Nd³⁺) or visible and near-infrared (Sm³⁺, Pr³⁺) spectral regions were synthesized and characterized using various methods, including single crystal X-ray diffraction. The study demonstrated that both tris complexes [LnQ^cy₃(H₂O)(EtOH)] and tetrakis-acids [H₃O][LnQ^cy₄] can be synthesized by varying the synthetic conditions. The photochemical properties of the complexes were investigated experimentally and theoretically using various molecular spectroscopy techniques and Judd–Ofelt theory. The objective was to quantitatively and qualitatively disclose the influence of complex stoichiometry on its luminescence properties. The study showed that the addition of an extra ligand molecule (in the tetrakis species) increased molar extinction by up to 2 times, affected the shape of photoluminescence spectra, especially of the Pr³⁺ complex, and increased the quantum yield of the Sm³⁺ complex by up to 2 times. The results obtained from this study provide insights into the luminescent properties of lanthanide coordination compounds, which are crucial for the design and development of novel photonic materials with tailored photophysical properties. Full article

The physicochemical, optical, and luminescent properties and structures of glasses of the Ga₂S₃-GeS₂-Sb₂S₃:Pr system have been studied in a wide range of concentrations of the main components in order to reveal their correlation with the composition. According to the calculations using the Judd–Ofelt theory, glasses with a high content of Sb₂S₃ should provide the highest luminescence efficiency of Pr³⁺ ions. However, this result is leveled by enhancing the concentration quenching effect, followed by an increase of the Sb₂S₃ content in the glasses. The introduction of Pr leads to a significant increase in the fraction of Sb-Sb, Sb-Ge, Ge-Ge bonds in glasses enriched with Sb₂S₃ and GeS₂. In the cases of the glasses enriched with Ga₂S₃, this effect was not observed, apparently because Ga promotes the formation of three-coordinated sulfur atoms. Full article

ZrO₂ is an attractive host matrix for luminescence material because of its excellent physical properties, such as low phonon energy and wide band gap. In this work, the highly transparent Tm₂O₃ and Yb₂O₃ co-doped yttria stabilized zirconia (YSZ) (abbreviated as Yb/Tm: YSZ) single crystals were grown by the optical floating zone method. The Yb/Tm: YSZ samples were stabilized in the cubic phase at room temperature when Yb³⁺ and Tm³⁺ replaced Y³⁺. The influence of Yb³⁺ co-doping on the up-conversion luminescence properties of the crystals was systematically studied. A total of 0.5 mol% Tm₂O₃ and 2.0 mol% Yb₂O₃ co-activated YSZ single crystal (abbreviated as 2.0Yb/Tm: YSZ) has the maximum luminous intensity. There were seven absorption peaks located at around 358, 460, 679, 783.3, 850–1000, 1200, and 1721.5 nm that were observed in the absorption spectrum of the 2.0Yb/Tm: YSZ single crystal. There were three up-conversion peaks at around 488, 658 and 800 nm that were observed when the Yb/Tm: YSZ samples were excitated at 980 nm. The fluorescence lifetime of Tm³⁺ for the ¹G₄→³H₆ transition of the 2.0Yb/Tm: YSZ sample is 7.716 ms as excited with a 980 nm laser. In addition, the oscillator strength parameters Ω_λ (λ = 2, 4 and 6) of this sample were derived by the Judd–Ofelt theory to evaluate the laser performance of the host materials. The ratio Ω₄/Ω₆ of this sample is 0.80, implying its excellent laser output. Therefore, the 2.0Yb/Tm: YSZ single crystal is a considerable potential material for laser and luminescence applications. Full article

The spectroscopic properties of Eu³⁺-doped Bi₁₂SiO₂₀ (BSO) were investigated and compared with that of Eu³⁺-doped Bi₁₂GeO₂₀ (BGO). The emission properties and the absorption spectra have been measured at 10 K as well as at 300 K (room temperature). Luminescence was detected due to the direct excitation of the ⁵D₀ level of Eu³⁺, as well as through the excitation of the ⁵D₁ level. The Judd–Ofelt theoretical framework was used to compute the radiative lifetimes (τ) and the omega parameters (Ω_λ). The electric dipole transition probabilities, asymmetry ratios (R), along with the branching ratios (β) were also determined based on the obtained experimental data. The strongest detected luminescence belongs to the ⁵D₀ → ⁷F₀ transition observed at 578 nm, similar to the BGO sillenite. Reasons for the major presence of the ⁵D₀ → ⁷F₀ emission, theoretically forbidden by the Judd–Ofelt Theory, were investigated and compared with that of the BGO sillenite. Obtained results showed that the strong ⁵D₀ → ⁷F₀ line is also present in Eu:BSO, indicating that this is a feature of the entire sillenite family and not just Eu:BGO. Full article

A new strategy for the easy polymerization of anionic [Ln(Q^cy)₄]⁻ (HQ^cy-4-(cyclohexanecarbonyl)-5-methyl-2-phenyl-2,4-dihydro-3H-pyrazol-3-one) into two-dimensional layers of [AgLn(Q^cy)₄]_n (Ln = Sm, Eu, Gd, Tb and Dy) is proposed by binding the single molecular anions [Ln(Q^cy)₄]⁻ to silver cations through the coordination of the pyridinic nitrogen atoms of the pyrazolonate rings. The luminescent properties of [AgLn(Q^cy)₄]_n have been studied in detail, and it was shown that the previously described low photoluminescence quantum yield (PLQY) of [Eu(Q^cy)₄]⁻ is due to Ligand-To-Metal Charge Transfer (LMCT) quenching, which is effectively suppressed in the heterometallic [AgEu(Q^cy)₄]_n polymer. Sensibilization coefficients for H₃O[Eu(Q^cy)₄], [AgEu(Q^cy)₄]_n, and H₃O[Sm(Q^cy)₄] complexes (n ≈ 1) were estimated via theoretical analysis (also by using Judd-Ofelt theory for Sm³⁺) and PLQY measurements. Full article

Borogermanate glasses singly doped with Dy³⁺ ions were synthesized and then studied using the absorption and luminescence spectra. Spectroscopic changes of Dy³⁺ ions have been examined for compositional-dependent glasses with various molar ratios GeO₂:B₂O₃. In this work, several spectroscopic parameters of Dy³⁺ ions were obtained experimentally and compared to the calculated values from the Judd–Ofelt theory. Luminescence spectra measured for borogermanate glasses consist of blue, yellow and red bands, which correspond to ⁴F_9/2 → ⁶H_15/2, ⁴F_9/2 → ⁶H_13/2 and ⁴F_9/2 → ⁶H_11/2 transitions of Dy³⁺, respectively. Luminescence lifetimes for the ⁴F_9/2 excited state are reduced, whereas the stimulated emission cross-sections for the most intense ⁴F_9/2 → ⁶H_13/2 yellow transition of Dy³⁺ increase with increasing GeO₂ and decreasing B₂O₃ concentrations in glass-hosts. Quantum efficiency of the ⁴F_9/2 (Dy³⁺) excited state is nearly independent on molar ratios GeO₂:B₂O₃. Attractive spectroscopic properties related to the ⁴F_9/2 → ⁶H_13/2 transition of Dy³⁺ ions are found for borogermanate glasses implying their potential utility for yellow laser action and solid-state lighting technology. Full article

Luminescent materials with high thermal stability and quantum efficiency are extensively desired for indoor illumination. In this research, a series of Eu³⁺-activated KGd₂F₇ red-emitting nanoparticles were prepared at room temperature and their phase structure, morphology, luminescence properties, as well as thermal stability, have been studied in detail. Excited by 393 nm, the resultant nanoparticles emitted bright red emissions and its optimal status was realized when the Eu³⁺ content was 30 mol%, in which the concentration quenching mechanism was triggered by electric dipole–dipole interaction. Through theoretical analysis via the Judd–Ofelt theory, one knows that Eu³⁺ situates at the high symmetry sites in as-prepared nanoparticles. Moreover, the internal and extra quantum efficiencies of designed nanoparticles were dependent on Eu³⁺ content. Furthermore, the studied nanoparticles also had splendid thermal stability and the corresponding activation energy was 0.18 eV. Additionally, via employing the designed nanoparticles as red-emitting constituents, a warm white light-emitting diode (white-LED), which exhibits low correlated color temperature (4456 K), proper luminous efficiency (17.2 lm/W) and high color rendering index (88.3), was developed. Our findings illustrate that Eu³⁺-activated KGd₂F₇ nanoparticles with bright red emissions are able to be used to promote the performance of white-LED. Full article

Single crystals of Tb³⁺ single-doped and Tb³⁺/Pr³⁺ co-doped CaYAlO₄ were produced by the Czochralski method. The room-temperature polarized absorption spectra, emission spectra, and decay curves were recorded and analyzed in detail. The absorption cross-section around 487 nm was found to be 1.53 × 10⁻²² cm² for the π polarization in the Tb³⁺:CaYAlO₄ crystal and increased to 5.23 × 10⁻²² cm² in the Tb³⁺/Pr³⁺:CaYAlO₄ crystal. The spectroscopic parameters were calculated through the Judd–Ofelt theory. For the Tb³⁺:CaYAlO₄ crystal, the emission bands of green light at 546 nm and yellow light at 587 nm had fluorescence branching ratios of 64.7% and 6.65% with cross-sections of 8.82 × 10⁻²² cm² (σ-polarization) and 0.44 × 10⁻²² cm² (π-polarization), respectively. The decay lifetimes of ⁵D₄ multiplets were measured to be 1.41 ms and 1.1 ms for Tb³⁺:CaYAlO₄ and Tb³⁺/Pr³⁺:CaYAlO₄ crystals, respectively. The energy transfer mechanisms of Tb³⁺ and Pr³⁺ and their emission spectral intensities at different temperatures were analyzed. As the temperature increased, the luminescence intensity of the Tb³⁺:CaYAlO₄ and Tb³⁺/Pr³⁺:CaYAlO₄ crystals decreased almost linearly with the CIE coordinate variation, from (0.370, 0.621) to (0.343, 0.636) and from (0.345, 0.638) to (0.246, 0.698), respectively. The results indicate the potential of Tb³⁺:CaYAlO₄ and Tb³⁺/Pr³⁺:CaYAlO₄ crystals as visible laser materials with a wide temperature range. Full article

The Er_1.5Y_1.5Al₅O₁₂ (Er:YAG) and (Er_1.43Y_1.43Sc_0.14)(Sc_0.24Al_1.76)Al₃O₁₂ (Er:YSAG) ceramics have been characterized using the Judd-Ofelt (JO) theory. The line strengths and oscillator strengths of several transitions from the ground state ⁴I_15/2 to excited state manifolds have been evaluated from transmittance spectra measured at room temperature (300 K). The JO parameters have been calculated, and the values of the radiative decays rate and the radiative lifetimes for the ⁴I_13/2 excited state, and the luminescence cross-section of ⁴I_15/2 → ⁴I_13/2 in Er-doped ceramic samples have been established. We have traced the influence of Sc³⁺ inclusion on spectroscopic properties and crystal quality and estimate prospects of application in laser systems. Full article

For the near-infrared emission, Er³⁺ and Er³⁺/Yb³⁺ co-activated borate based glass hosts were synthesized by the method of melting andquenching. The emission intensity was maximum for 0.5 mol% Er³⁺ singly activated glass in the near-infrared (NIR) region covering the telecommunication window. The 2 mol% of Yb³⁺ co-doping enhanced the emission gain cross-section of the glass by two times contrast to 0.5 mol% Er³⁺ loaded glass. This enhancement shifted to lower spectral regions when P increased from 0 to 1. The effect of Yb³⁺ loading on the gain cross-section of the Er³⁺ co-activated glasses was analyzed using the McCumber theory. The results showed that the 0.5Er2Yb glass has a flat gain in the range of 1460–1640 nm, this suggest a lower pump threshold is enough to perform the laser functioning of a 1530 nm band and optical window of telecommunication applications. Full article

In this paper, Er:Y₂O₃ optical ceramics were fabricated and details of the synthesis were presented. The spectral–luminescent properties of Er³⁺:Y₂O₃ optical ceramics were investigated. The absorption and emission cross-section spectra were determined. The luminescence kinetics at near 1.6 µm was single exponential and the lifetime of erbium ⁴I_13/2 energy level was determined. In the frame of the conventional Judd–Ofelt theory, the emission properties of the energy levels of erbium ⁴I_13/2 and ⁴I_11/2 involved in laser operation at near 1.6 µm were calculated. The gain coefficient curves for typical values of the relative population of the upper laser level ⁴I_13/2 were presented. The composition and structure were studied using the SEM, XRD, FTIR spectroscopy, and X-ray computer tomography techniques. Full article