Reduction and luminescence of europium ions in glass ceramics containing SrF2 nanocrystals

Reduction of Eu³⁺ → Eu²⁺ and luminescence of europium (Eu) ions in glass ceramics containing SrF₂ nanocrystals have been investigated. The formation of SrF₂ nanocrystals in glass ceramics was confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Blue luminescence of the Eu²⁺ ions was observed in the Eu doped glass ceramics which were prepared by the heat treatment of the glass in air atmosphere. The double-exponential decay curves of ⁵D₀ state of Eu³⁺ in the Eu doped glass ceramics indicated that there were two different surroundings of the Eu ions in the glass ceramics.     

Broadband infrared luminescence of Ni-doped silicate glass-ceramics containing lithium aluminate spinel nanocrystals

Transparent Ni²⁺-doped SiO₂-Al₂O₃-Ga₂O₃-Li₂O (LGAS) glass-ceramics embedding lithium aluminate spinel nanocrystals was prepared. After heat treatment, LiAl₅O₈ crystallite was precipitated in the glasses, and its size was about 3 nm. It was confirmed from the absorption spectra that the ligand environment of Ni²⁺ ions changed from the trigonal bi-pyramid fivefold sites in the as-made glass to the octahedral sites in the glass-ceramics. Upon excitation at 980 nm, broadband infrared luminescence centered at around 1250 nm with full width at half maximum (FWHM) more than 250 nm was observed originating from the ³T₂(³F) → ³A₂(³F) transition of Ni²⁺ in octahedral sites. The broadband near-infrared (NIR) emission from Ni²⁺-doped glass-ceramics can be as host materials for broadband optical amplifier.     

Spectroscopic properties of Er-Yb co-doped glass ceramics containing BaF2 nanocrystals

A Er³⁺ and Yb³⁺ co-doped transparent oxyfluoride glass ceramic containing BaF₂ nanocrystals has been prepared. The formation of BaF₂ nanocrystals in the glass ceramic was confirmed by X-ray diffraction. Intense upconversion luminescence in the Er³⁺ and Yb³⁺ co-doped glass ceramic could be observed. Stark splitting of the Er³⁺ upconversion luminescence peaks in the glass ceramic indicated that Er³⁺ and Yb³⁺ had been incorporated into the BaF₂ nanocrystals. Near infrared luminescence decay curves showed that the Er³⁺ and Yb³⁺ co-doped glass ceramic had higher luminescence efficiency than the precursor glass.     

Enhanced mid-IR luminescence of Tm3+ ions in Ga2S3 nanocrystals embedded chalcohalide glass ceramics

Chalcohalide glass with a composition of 65GeS₂–25Ga₂S₃–10CsI (in mol%) doped with 0.6 wt% Tm³⁺ ions was prepared by conventional melt–quench method. By heat treating the precursor glass at 20 °C above its glass transition temperature T_g for different durations, IR transparent glass ceramics were obtained. X-ray diffraction (XRD) and scanning electron microscope (SEM) showed that Ga₂S₃ crystallites were precipitated after heat treatment and their grain sizes were in nano-scale and increased with the elongation of heat treated time. Mid-IR luminescence properties of the glass and transparent glass ceramic samples were investigated. The emissions at 2.3 and 3.8 μm corresponding to optical transitions of ³H₄ → ³H₅ and ³H₅ → ³F₄ of Tm³⁺ ions were significantly enhanced by the presence of Ga₂S₃ nanocrystals and reached a maximum after 8 hours treatment.     

Enhanced luminescent properties of Tb3+ ions in transparent glass ceramics containing BaGdF5 nanocrystals

Tb³⁺ doped transparent oxyfluoride glass ceramics containing BaGdF₅ nanocrystals were prepared. The transmission spectra, photoluminescence spectra, decay time and X-ray excited luminescence spectra of the Tb³⁺-doped glass and glass ceramics were investigated. Energy transfer from Gd³⁺ to Tb³⁺ has been observed in the glass and glass ceramics. The emission intensity of green band (⁵D₄ → ⁷F_J) of the Tb³⁺-doped glass ceramics is enhanced compared with that of the glass under ultraviolet and X-rays, which could be attributed to that the generation of BaGdF₅ nanocrystals with low phonon energy reduces the non-radiative transitions.     

Short-wavelength upconversion luminescence of Yb/Tm co-doped glass ceramic containing SrF2 nanocrystals

The preparation process and upconversion luminescence properties of the Yb³⁺ and Tm³⁺ co-doped glass ceramic containing SrF₂ nanocrystals were investigated. In the glass ceramic, the SrF₂ nanocrystals were embedded uniformly in the glass matrix. The Yb³⁺ and Tm³⁺ ions could be enriched into the precipitated SrF₂ nanocrystalline phase, which provide much lower phonon energy than the glass matrix. The glass ceramic exhibited much stronger upconversion luminescence from ultraviolet to visible than the precursor glass. The upconversion luminescence mechanisms were mainly attributed to Yb³⁺-Yb³⁺ cooperative upconversion, Yb³⁺-Tm³⁺ energy transfer and Tm³⁺-Tm³⁺ cross relaxation.     

Intense red and cyan luminescence in europium doped silicate glasses

The photoluminescence properties of silicate glasses, singly doped with europium ions and co-doped with europium ions and Al powder, have been characterized by the absorption, excitation, and emission spectroscopies. The absorption edge in the absorption spectra shows a large red shift from 320 nm to 405 nm. Under near-ultraviolet (NUV) excitation, sample, doped with Eu³⁺ emit intense red light while those co-doped with Eu³⁺ and Al give intense cyan emission. The influences of the glass compositions on the spectroscopic properties are also discussed. These glasses may be potential candidates for light-emitting diodes (LEDs).     

Photoluminescence of Sm3+, Dy3+, and Tm3+-doped transparent glass ceramics containing CaF2 nanocrystals

Photoluminescence properties of Sm³⁺, Dy³⁺, and Tm³⁺-doped transparent oxyfluoride silicate glass ceramics containing CaF₂ nanocrystals were reported. Emission bands of ⁴G_5/2 → ⁶H_5/2 (562 nm), ⁴G_5/2 → ⁶H_7/2 (598 nm), ⁴G_5/2 → ⁶H_9/2 (645 nm) and ⁴G_5/2 → ⁶H_11/2 (706 nm) for the Sm³⁺: glass and glass ceramic, with an excitation at ⁶H_5/2 → ⁴F_7/2 (402 nm) have been recorded. Of them, ⁴G_5/2 → ⁶H_7/2 (598 nm) has shown a bright orange emission. With regard to the Dy³⁺: glass, a bright fluorescent yellow emission at 575 nm (⁴F_9/2 → ⁶H_13/2) and blue emission at 481 nm (⁴F_9/2 → ⁶H_15/2) have been observed, apart from 662 nm (⁴F_9/2 → ⁶H_11/2) emission transition with an excitation at 386 nm (⁶H_15/2 → ⁴I_13/2 + ⁴F_7/2) wavelength. Emission bands of ¹G₄ → ³F₄ (650 nm) and ¹G₄ → ³H₅ (795 nm) transitions for the Tm³⁺: glass and glass ceramic, with an excitation at ³H₆ → ¹G₄ (467 nm) have been observed. Of them, ¹G₄ → ³F₄ (650 nm) has shown bright red emission. Decay lifetime measurements were also carried out for all the observed Sm³⁺, Dy³⁺, and Tm³⁺-doped glass and glass ceramic emission bands.     

Spectroscopic properties and simulation of white-light in Dy-doped silicate glass

Spectroscopic properties of various concentrations Dy³⁺-doped silicate glasses were characterized by excitation and emission spectra. The optimal doping concentration of Dy³⁺ ions was found to be 3.0 wt%, and the nature of resonance energy transfer was confirmed to be electric dipole-dipole interaction according to Huang’s rule. Simulation of white-light for these glasses was also performed by varying the excitation wavelength. The results show that the white-light luminescence color could be tuned to various wavelength excitations, and the present silicate glass is more suitable for generation of white-light for blue LED chips.     

Wet chemical synthesis and sintering of rare earth phosphate ceramics (Y0.3Ce0.7PO4: Tb) and their green luminescence properties

Hexagonal and monoclinic phase yttrium/cerium phosphates with terbium dopants have been prepared successfully through co-precipitation and calcination approaches. Their crystal structure properties were studied by X-ray diffraction (XRD), Scanning Electronic Microscope (SEM) and Dynamic Light Scattering (DLS). Fluorescence excitation and emission spectra exhibited improved luminescence properties by increasing the terbium content in the micron-meter crystals. In addition, Y_0.3Ce_0.7PO₄: Tb was embedded in colloidal sols and strong green emission was obtained in the presence of water atoms or hydroxyl groups.     

Stark splitting of the ground state of Er in fluorozirconate glass at low temperature

Optical properties of Er³⁺-doped ZBLAN glass matrix have been studied by luminescence spectroscopy under 488 nm excitation. The spectrum of the ⁴S_3/2⁴I_15/2 transition, carried out at temperature T = 2 K, shows a new line in the lowest energy region. This new line, centered at 17 996 cm⁻¹, was attributed to the lower transition between the Stark components of the ⁴S_3/2⁴I_15/2 transition. Measurements from T = 2 K to room temperature show the disappearance of this new line. From the results we estimate the splitting of 415 cm⁻¹ for the ground state and 100 cm⁻¹ for the ⁴S_3/2 excited multiplet. The experimental result allows us to assign the positions of the eight Stark components of the ground state multiplet of the Er³⁺ in the ZBLAN glass matrix.     

Er-doped silica–hafnia films for optical waveguides and spherical resonators

In this paper we present some result on sol–gel derived silica–hafnia systems. In particular we focus on fabrication, morphological and spectroscopic assessment of Er³⁺-activated thin films. Two examples of silica–hafnia-derived waveguiding glass ceramics, prepared by top–down and bottom–up techniques are reported, and the main optical properties are discussed. Finally, some properties of activated microspherical resonators, having a silica core, obtained by melting the end of a telecom fiber, coated with an Er³⁺-doped 70SiO₂–30HfO₂ film, are presented.     

Deep level defect luminescence in cadmium selenide nano-crystals films

Undoped CdSe monocrystals and CdSe nano-crystals films have been studied at various temperatures by continuous wave (cw) photoluminescence. We report on a characteristic deep level emission, which is consistently observed in the wurtzite bulk- and nanocrystalline forms of CdSe. Two broad luminescence bands, which are separated from the excitonic emission by 0.5 and 0.7 eV occur in CdSe, prepared by quite different techniques. These bands experience, similar to the excitonic emission, a spectral shift to high energy enforced by the quantum confinement in nano-CdSe. The defects responsible for this luminescence are probably two different V_Cd–V_Se divacancies: one is oriented along the hexagonal c-axis, the other is oriented along the basal Cd–Se bond directions.     

1540 nm fiber laser excited upconversion luminescence in erbium-doped lead-fluoride nanocrystals

Upconversion luminescence in erbium-doped PbGeO₃-PbF₂-CdF₂-based vitroceramic under 1540 nm infrared excitation is investigated. Luminescence signals around 410, 525, 550, 660 and 850 nm were generated and attributed to the ²H_9/2, ²H_11/2, ⁴S_3/2 and ⁴F_9/2 transitions to the ⁴I_15/2 ground-state, and ⁴S_3/2-⁴I_13/2, respectively. The erbium ions excited-state emitting levels were populated through a combination of stepwise ground-state absorption, phonon-assisted excited-state absorption and cross-relaxation processes. The results also disclosed that all emission signals obtained with vitroceramic samples presented intensities three times higher when compared to the precursor glass samples. In addition, the red emission signal at 660 nm for 1540 nm pumping exhibited an expressively high intensity when compared to the green signal.     

Optical properties of PbSe quantum dots doped in borosilicate glass

PbSe quantum dots (QDs) were synthesized in borosilicate glass and their optical properties were investigated. The typical quantum confinement effects were clearly observed from the absorption when the average radii of the QDs changed from 1.7 to 3.1 nm. Photoluminescence from PbSe QDs was achieved in 1.1–2.2 μm wavelength region that covers the entire fiber-optic telecommunication window. Borosilicate glasses containing controlled size of PbSe QDs provide potentials for the fiber-optic amplifiers.     

Surface plasmon excited infrared-to-visible upconversion in Er-doped transparent glass ceramics

The surface plasmon (SP) excited infrared-to-visible upconversion luminescence has been studied in the oxyfluoride glass ceramics containing Er³⁺-doped fluoride nano-crystals. Upconversion luminescence was observed at glass ceramics. Quantum yield of upconversion luminescence increased with increasing heat-treatment temperature. The transparent glass ceramics heat-treated at 700 °C was covered with a 50 nm gold film, and then attached to an SF10 prism with index-matching oil to make an attenuated total reflection (ATR) illumination. The intense upconversion luminescence bands at 540 and 660 nm were observed at the SP resonance angle by using p-polarized laser beam. The apparent dependences of the upconversion efficiency on laser polarization and on incident angle demonstrated the SP excited upconversion of Er³⁺.     

Crystallization and spectroscopic properties of Eu-doped CaF2 nanocrystals in transparent oxyfluoride glass-ceramics

Transparent oxyfluoride glass-ceramic in the system SiO₂–Al₂O₃–CaF₂–EuF₂ containing Eu-doped CaF₂ nanocrystals were produced by using the controlled crystallization of melt-quenched glass. X-ray diffraction and transmission electron microscopy data have revealed the formation of the CaF₂ nanocrystals of about 65 nm size. Photoluminescence spectra have shown an increase of the splitting of the luminescences associated to the Eu³⁺ ion along with annealing time which is consistent with the Eu³⁺ environment evolving from a glassy to a crystalline state.     

Estimation of shear-banding resistance in metallic glass containing nano-crystalline particles

Bulk metallic glasses (BMGs) have a variety of excellent properties compared with the majority of conventional crystalline alloys. However, they exhibit limited global plasticity at room temperature because of shear banding. Several methods have been proposed to improve the limited ductility of BMG; one method is the homogeneous distribution of crystalline particles. However, our understanding of the interaction between the crystalline particles and shear bands (SB) is not sufficient. Here, we performed molecular dynamics (MD) simulations of mode II deformation of a notched BMG plate and BMG plates containing one nano-crystalline particle ahead of the notch bottom. To compare the effect of crystalline particle size on the resistance to SB propagation, we used the J-integral. By comparing J-R curves and the deformation behavior of the BMG plates with and without nano-crystalline particles, we found that the resistance to shear banding is efficiently improved by introducing crystalline particles with sufficient size, compared to the SB width.     

Luminescence behavior of Er ions in glass-ceramics containing CaF2 nanocrystals

The upconversion luminescence and near infrared luminescence of the Er³⁺ ions in transparent oxyfluoride glass-ceramics containing CaF₂ nanocrystals have been investigated. The formation of CaF₂ nanocrystals in the glass-ceramics was confirmed by XRD. The oscillator strengths for several transitions of the Er³⁺ ions in the glass and glass-ceramics have been obtained and then the Judd-Ofelt parameters were calculated. The split near infrared emission peaks of the Er³⁺ ions in the glass-ceramics can be observed because the Er³⁺ ions have been incorporated into crystalline environment of the CaF₂ nanocrystals. The upconversion luminescence intensity of Er³⁺ ions in the glass-ceramics increased significantly with increasing heat treated time. The transition mechanism of the upconversion luminescence has been ascribed to a two-photon absorption process.     

The effect of PbF2 content on the microstructure and upconversion luminescence of Er-doped SiO2-PbF2-PbO glass ceramics

The Er³⁺ doped transparent oxyfluoride glass ceramics were obtained by appropriate heat treatment of the precursor glasses with composition (mol%) 50SiO₂-xPbF₂-(50 − x)PbO-0.5ErF₃. The microstructure and optical properties of the glasses and glass ceramics were determined by differential scanning calorimetry (DSC), X-ray diffraction (XRD), absorption spectra and luminescence spectra. The intensity of upconversion luminescence significantly increased in glass ceramics compared to that in precursor glass. The emission bands centered around 660 nm (⁴F_9/2 → ⁴I_15/2) and 410 nm (²H_9/2 → ⁴I_15/2) were simultaneously observed in glass ceramics but cannot be seen in the corresponding precursor glass. The influence of different PbF₂ content on the microstructure and upconversion luminescence of the samples was analyzed in detail. The results indicated that with the increase of PbF₂ content, the Ω₂ was almost the same and the ratios of red to green upconversion luminescence decreased in glass ceramics.