Search Results (74)

We have investigated the structural, morphological, magnetic, and up-conversion luminescence properties of the Yb³⁺/Er³⁺-doped LiGdF₄ nanocrystals precipitated in the silica glassy matrix. Morphological analysis showed uniform distribution of LiGdF₄ nanocrystals (tens of nm in size), embedded in silica glass matrix. FTIR spectroscopy analysis showed trifluoracetates thermolysis with silica lattice formation and structural analysis by XRD is consistent with the LiGdF₄ crystallization process, most likely through an autocatalytic reaction. The stress and crystalline lattice distortion are assigned to the doping and glass matrix environment where the growth process occurs. The EPR spectra associated with the Gd³⁺ ions have shown a well-defined spectrum in the xerogel, associated with the trifluoroacetate ligand environment. In the LiGdF₄ nanocrystals, the broad and unresolved spectrum is due to an envelope of unresolved anisotropic fine structure and a high dipole–dipole interaction between the Gd³⁺/Yb³⁺/Er³⁺ paramagnetic ions. Under 980 nm laser light pumping, we observed the characteristic “blue”, “green” and “red” up-conversion luminescences of the Er³⁺ ions through Yb → Er energy transfer process, that imply three and two-photon process; near UV up-conversion luminescence of Gd³⁺ is observed at about 280–300 nm where Yb → Er and Er → Gd energy transfer is involved. The UC luminescence properties can be improved up to two times by additional Yttrium co-doping due to the induced crystal field distortion. Full article

In this study, we investigate the presence of the Griffiths-like anomaly in the geometrically frustrated antiferromagnet ${\mathrm{HoBaCo}}_4$${\mathrm{O}}_{7+\delta }$ and globally its absence in ${\mathrm{ErBaCo}}_4$${\mathrm{O}}_{7+\delta }$, despite only small differences in the ionic radii, f-electron occupancy, and the corresponding crystal structures of the ${\mathrm{Ho}}^{3+}$ and ${\mathrm{Er}}^{3+}$-members. Previous studies have identified the Griffiths phase in the Dy-analog, ${\mathrm{DyBaCo}}_4$${\mathrm{O}}_{7+\delta }$, suggesting certain inherent features of this class of materials that regularly give rise to such anomalies. To explore the curious disappearance of such an anomalous feature in ${\mathrm{ErBaCo}}_4$${\mathrm{O}}_{7+\delta }$, we prepared a series of compounds with varying compositions ${\mathrm{Ho}}_{1-x}$${\mathrm{Er}}_x$${\mathrm{BaCo}}_4$${\mathrm{O}}_{7+\delta }$ ($0\le x\le 1$) and systematically studied the evolution of various physical properties as a function of Er-doping. Our experimental studies, including X-ray diffraction (XRD), magnetic, X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), heat capacity, and muon spin relaxation spectroscopy ($\mu$SR spectroscopy), revealed that while the Griffiths-like anomaly indeed disappears with doping at the macroscopic level, signatures of inhomogeneity are retained in ${\mathrm{ErBaCo}}_4$${\mathrm{O}}_{7+\delta }$ too, at least at the local level. Overall, our results highlight the significant role of ionic radius and local structural distortions in stabilizing the Griffiths phase in this class of systems. Full article

Random lasers (RLs) based on glasses and glass-ceramics doped with rare-earth ions (REI) deserve great attention because of their specific physical properties such as large thermal stability, possibility to operate at high intensities, optical wavelength tunability, and prospects to operate Fiber-RLs, among other characteristics of interest for photonic applications. In this article, we present a brief review of experiments with RLs based on tellurite and germanate glasses and glass-ceramics doped with neodymium (Nd³⁺), erbium (Er³⁺), and ytterbium (Yb³⁺) ions. The glass samples were fabricated using the melt-quenching technique followed by controlled crystallization to achieve the glass-ceramics. Afterwards, the samples were crushed to obtain the powder samples for the RLs experiments. The experiments demonstrated RLs emissions at various wavelengths, with feedback mechanisms due to light scattering at grain/air and crystalline/glass interfaces. The phenomenon of replica symmetry breaking was verified through statistical analysis of the RLs intensity fluctuations, indicating a photonic phase-transition (corresponding to the RL threshold) analogous to the paramagnetic-to-spin glass transition in magnetic materials. The various results reported here highlight the potential of glasses and glass-ceramics for the development of RLs with improved performance in terms of reduction of laser threshold and large lifetime of the active media in comparison with organic materials. Full article

A BaF₂ single crystal co-doped with Er³⁺ and Yb³⁺ was grown by the vertical Bridgman technique and investigated for its optical and dielectric properties. Judd–Ofelt analysis yielded intensity parameters Ω₂ = 0.59, Ω₄ = 0.38, and Ω₆ = 0.27 (×10⁻²⁰ cm²), with a quality factor χ = 1.41, indicating strong radiative transitions. Under UV and near-UV excitation, emissions at 321, 405, 518, and 536 nm were observed, with radiative lifetimes ranging from 1.1 to 3.4 ms. A single dielectric relaxation process was identified, with activation energy of 0.58 eV and associated with trigonal NNN dipoles. The NNN dipole concentration was estimated at ~2.5 × 10¹⁸ cm⁻³. These results support the suitability of Er³⁺,Yb³⁺ co-doped BaF₂ crystals for luminescent and dielectric applications in advanced photonic materials. Full article

Upconversion luminescent materials (UCLMs) have garnered significant attention due to their broad potential applications in fields such as display technology, biological imaging, and optical sensing. However, optimizing crystal phase and morphology remains a challenge. This study systematically investigates the effects of phase transformation and morphology control on the upconversion luminescent properties of K₃GaF₆:Er³⁺. By comparing different synthesis methods, we found that the hydrothermal method effectively facilitated the transformation of the Na_xK_3-xGaF₆ crystal phase from cubic to monoclinic, with Na⁺/K⁺ ions playing a key role in the preparation process. Furthermore, the hydrothermal method significantly optimized the particle morphology, resulting in the formation of uniform octahedral structures. The 657 nm red emission intensity of the monoclinic phase sample doped with Er³⁺ was enhanced by 30 times compared to that of the cubic phase, clearly demonstrating the crucial role of phase transformation in luminescent performance. This study emphasizes the synergistic optimization of crystal phase and morphology through phase engineering, which substantially improves the upconversion luminescence efficiency of K₃GaF₆:Er³⁺, paving the way for further advancements in the design of efficient upconversion materials. Full article

The performance optimization of photoluminescent (PL) materials is a hot topic in the field of applied materials research. There are many different crystal defects in photoluminescent materials, which can have a significant impact on their optical properties. The luminescent properties and chemical stability of materials can be effectively improved by adjusting lattice defects in crystals. We systematically studied the effect of doping ions on the energy transfer upconversion mechanism in different defect crystals by changing the matrix alkali metal ions. Meanwhile, the influence mechanism of crystal defect distribution on luminescence performance is explored by adjusting the ratio of Na–Li. The PL spectra indicate that changing the alkaline ions significantly affects the luminescence performance and efficiency of UCNPs. The change in ion radius leads to substitution or gap changes in the main lattice, which may alter the symmetry and strength of the crystal field around doped RE ions, thereby altering the UCL performance. Additionally, we demonstrated the imaging capabilities of the synthesized upconversion nanoparticles (UCNPs) in cellular environments using fluorescence microscopy. The results revealed that Na_0.9Li_0.1LuF₄–Yb, Er nanoparticles exhibited significantly enhanced fluorescence intensity in cell imaging compared to other compositions. We further investigated the mechanism by which structural defects formed by doping ions in UCNPs with different alkali metals affect energy transfer upconversion (ETU). This work emphasizes the importance of defect regulation in the ETU mechanism to improve the limitations of crystal structure on the luminescence performance and promote the future application of upconversion nanomaterials, which will provide important theoretical references for the exploration of high-performance luminescent materials in the future. Full article

This review delves into the forefront of upconversion luminescence (UCL) research, focusing on KY₃F₁₀-based compounds, particularly their cubic α-phase. These materials are renowned for their exceptional luminescent properties and structural stability, making them prime candidates for advanced photonic applications. The synthesis methods and structural characteristics of the existing works in the literature are meticulously analyzed alongside the transformative effects of various doping strategies on UCL efficiency. Incorporating rare earth (RE) sensitizer ions such as Yb³⁺, along with activator ions like Er³⁺, Ho³⁺, Nd³⁺, or Tm³⁺, researchers have achieved remarkable enhancements in emission intensity and spectral control. Recent and past breakthroughs in understanding the local structure and phase transitions of single-, double-, and triple-RE³⁺-doped KY₃F₁₀ nanocrystals are highlighted, revealing their pivotal role in fine-tuning luminescent properties. Furthermore, the review underscores the untapped potential of lesser-known crystal structures, such as the metastable δ-phase of KY₃F₁₀, which offers promising avenues for future exploration. By presenting a comprehensive analysis and proposing innovative research directions, this review aims to inspire continued advancements in the field of upconversion materials, unlocking new potentials in photonic technologies. Full article

As smart materials, electrorheological elastomers (EREs) formed by pre-treating active electrorheological particles are attracting more and more attention. In this work, four Mg-doped strontium titanate (Mg-STO) particles with spherical, dendritic, flake-like, and pinecone-like morphologies were obtained via hydrothermal and low-temperature co-precipitation. XRD, SEM, Raman, and FT-IR were used to characterize these products. The results showed that Mg-STOs are about 1.5–2.0 μm in size, and their phase structures are dominated by cubic crystals. These Mg-STOs were dispersed in a hydrogel composite elastic medium. Then, Mg-STO/glycerol/gelatin electrorheological composite hydrophilic elastomers were obtained with or without an electric field. The electric field response properties of Mg-doped strontium titanate composite elastomers were investigated. We concluded that dendritic Mg-STO composite elastomers are high-performance EREs, and the maximum value of their energy storage was 8.70 MPa. The significant electrorheological performance of these products is helpful for their applications in vibration control, force transducers, smart structures, dampers, and other fields. Full article

Er³⁺-doped fluorite crystals, including CaF₂ and SrF₂, are considered as attractive laser gain materials in the mid-infrared (MIR) region with merits of high laser efficiency as well as low doping concentration. In this work, a series of Er, La:CaF₂ crystals were grown and the modulation effect of co-doping La³⁺ ions on the spectral properties and mid-infrared laser performance was investigated. It was found that introducing La³⁺ ions can effectively manipulate the coordination environment of Er³⁺ ions embedded in CaF₂ crystal, thus modulating the shape and intensity of absorption and emission bands. On the other hand, La³⁺ ions can partially substitute Er³⁺ sites in the clusters to form mixed clusters, which affects the energy transfer processes between Er³⁺ ions as well as ~3 μm laser performance, which is dominated by energy transfer up-conversion (ETU) processes between Er³⁺ ions. By co-doping La³⁺ ions into Er:CaF₂ crystal at an appropriate concentration, the spectral parameter modulation can be achieved while maintaining a high MIR laser efficiency. Full article

In this study, we investigate micrometer-sized NaYF₄ crystals double-doped with Yb³⁺/Er³⁺ lanthanide ions, designed for temperature-sensing applications. In contrast to previous studies, which focused predominantly on the high-temperature regime, our investigation spans a comprehensive range of both high and ultralow temperatures. We explore the relationship between temperature and the upconversion luminescence (UCL) spectra in both frequency and time domains. Our findings highlight the strong dependence of these spectral characteristics of lanthanide-doped NaYF₄ crystals on temperature. Furthermore, we introduce a dual-mode luminescence temperature measurement technique, leveraging the upconversion emission intensity ratio for both green and red emissions. This study also examines the correlation between temperature sensing, energy level disparities, and thermal coupling in Er³⁺ ions across various temperature scales. Our research contributes to advancing the understanding and application of lanthanide-doped materials, setting a foundation for future innovations in temperature sensing across diverse fields. Full article

Gallium oxide (Ga₂O₃) is an emerging wide bandgap semiconductor promising a wide range of important applications. However, mass production of high-quality crystalline Ga₂O₃ still suffers from limitations associated with poor reproducibility and low efficiency. Low-temperature-grown amorphous Ga₂O₃ demonstrates comparable performance with its crystalline counterparts. Lanthanide Er³⁺-doped Ga₂O₃ (Ga₂O₃: Er) possesses great potential for developing light-emitting devices, photodetectors, solid-state lasers, and optical waveguides. The host circumstance can exert a crystal field around the lanthanide dopants and strongly influence their photoluminescence properties. Here, we present a systematical study of the impact of amorphous-to-crystalline transition on the upconversion photoluminescence in Ga₂O₃: Er thin films. Through controlling the growth temperature of Ga₂O₃: Er films, the upconversion luminescence of crystalline Ga₂O₃: Er thin film is strongly enhanced over 100 times that of the amorphous Ga₂O₃: Er thin film. Moreover, the variation of photoluminescence reflects the amorphous-to-crystalline transformation of the Ga₂O₃: Er thin films. These results will aid further designs of favorable optoelectronic devices integrated with lanthanide-doped Ga₂O₃ thin films. Full article

Structural changes of Er- or Yb-ion doped LiNbO₃ (LN) nanocrystals were studied in relation to the high-energy ball milling process. The evolution of the size of the particles and the formation of different phases were followed by dynamic light scattering and X-ray diffraction measurements, while the electronic transitions of rare-earth (RE) ions were investigated by absorption spectroscopy in the infrared spectral range. During the milling process, RE ions left the crystal lattice and an RE₂O₃ phase appeared to an increasing extent next to the LN. The change in the absorption spectra and the phases formed during the grinding process were found to be very similar for both investigated RE ions and were independent of their original concentration in the starting crystal samples. The extent of the RE loss was found to be 90% after 100 min of wet grinding. Full article

For purposes of optimizing the microstructure and fluorescence properties of rare-earth elements (REEs)-doped fluorapatites (FAps), various kinds of REEs (La, Pr, Sm, Eu, Gd, Ho, Er, and Yb) with the concentration of 2~20 mol.% have been inserted into the FAps framework via hydrothermal method, in order to investigate the influential mechanism of the REEs on the crystal structure, morphology, and fluorescence under the excitation of the near-ultraviolet light of the FAps. Experimental results show that the wavelength of the emitted light of the REEs-doped FAps is decided by the type of REEs. Unlike the Pr/Yb- and Ho-doped FAps and with the fluorescence of red and green emitted light, respectively, the Er-doped FAps show a blue light emission with wavelengths of 296, 401, and 505 nm, which is, moreover, different with the Eu-doped Faps, showing an orange light emission with wavelengths of 490, 594, and 697 nm. The emission luminous color is related to the lattice defects of the FAps doped with the various types and the effective doping concentration of the REEs. The luminous intensity increases with the increase in the effective doping concentration of the REEs. Nevertheless, the formation of rare-earth fluoride results in the decrease in the effective doping concentration of the REEs and the luminous intensity. The FAps with an effective doping concentration of 7 mol.% Er and 3 mol.% Eu show relative excellent fluorescence properties. Full article

Single crystal fibers combine the great specific surface area of fibers and the single crystal property of the bulk crystal which shows great potential for a high-power laser. For an Er-doped crystal, due to the fluorescence quenching at the 3 μm wavelength, high Er doping is necessary to increase the fluorescent up-conversion for the breaking limitation. However, a high Er doping concentration must lead to high heat accumulation, resulting in poor laser performance. Compared with an Er-doped bulk crystal, Er-doped SCF has the great potential to remove the heat in the crystal, and it is easy to obtain a high power. In this paper, Er: Y₃Sc₂Ga₃O₁₂ (Er: YSGG) single crystals were successfully grown using the micro-pulling-down method (μ-PD). Owing to the stably grown interface, the diameter of the crystal is 2 mm with a length up to 80 mm. Then, the measurements of Laue spots and Er³⁺ distribution indicated that our crystals have a high quality. Based on the as-prepared Er: YSGG SCF, the continuous-wave (CW) laser operations at 2794 nm were realized. The maximum output was 166 mW with a slope efficiency of up to 10.99%. These results show that Er: YSGG SCF is a suitable material for future high-power 3 μm laser operation. Full article

Single crystal fiber (SCF) is a novel solid gain medium and technique which combines the advantages of glass fiber and single crystal, showing great potential in the field of high-power lasers. In this paper, Er, Nd: YSGG single crystals with diameters of 2 mm and lengths of 80 mm were successfully grown using the micro-pulling-down method for the first time. Then, the measurements of Laue spots and Er³⁺ distribution indicated that the as-grown crystals were of a high quality. The effect of co-doped Nd³⁺ on the Er: YSGG was systematically discussed, which demonstrated that Nd³⁺ can decrease the fluorescence lifetime of Er: ⁴I_13/2 that solve the self-termination bottleneck accordingly. These results demonstrate that Er, Nd: YSGG SCFs are promising materials for the further 3 μm laser generations. Full article