Fabrication and optical properties of Y2O3-based ceramics with broad emission bandwidth

In this article, we report on the fabrication and optical properties of highly transparent yttria ceramics for lasers active media with broadband gain profile. Laser synthesis method was used to produce Y₂O₃-based nanopowders doped with 1 mol.% Nd³⁺ or Yb³⁺ for these transparent ceramics. The additives of sesquioxides Lu₂O₃ and Sc₂O₃ were used along with ZrO₂ to disorder the crystalline structure. The porosity and average grain size decrease with these additives and the emission bandwidths of Nd³⁺ (⁴F_3/2 → ⁴I_11/2) and Yb³⁺ (²F_5/2 → ²F_7/2) transitions widen to 40 and 60 nm, respectively. Laser operation with the slope efficiency of 29% was obtained in [(Yb_0.01Lu_0.24Y_0.75)₂O₃]_0.88(ZrO₂)_0.12 ceramic sample.     

Near‐Infrared and Upconversion Luminescence in Er:Y2O3 Ceramics under 1.5 μm Excitation

Results of the spectroscopic characteristics and upconversion luminescence in Er³⁺ doped yttria (Y₂O₃) transparent ceramics prepared by a modified two‐step sintering method are presented. The near‐infrared (1.5 μm) luminescence properties were evaluated as a function of Er³⁺ concentration. Judd–Ofelt intensity parameters, radiative rates, branching ratios, and emission lifetimes were determined and compared with results reported for Er³⁺‐doped Y₂O₃ single crystal and nanocrystals. Following pumping at 1.532 μm, weak blue (~0.41 μm, ²H_9/2 → ⁴I_15/2), strong green (~0.56 μm, ²H_11/2, ⁴S_3/2 → ⁴I_15/2), and red (~0.67 μm, ⁴F_9/2 → ⁴I_15/2) emission bands were observed as well as weak near‐infrared emissions at 0.8 μm (⁴I_9/2 → ⁴I_15/2) and 0.85 μm (⁴S_3/2 → ⁴I_13/2) at room temperature. The upconversion luminescence properties under ~1.5 μm pumping were further investigated through pump power dependence and decay time studies. Sequential two‐photon absorption leads to the ⁴I_9/2 upconversion emission, whereas energy‐transfer upconversion is responsible for the emission from the higher excited states ²H_9/2, ²H_11/2, ⁴S_3/2, and ⁴F_9/2. The enhanced red emission with increasing Er³⁺ concentration most likely occurred via the cross‐relaxation process between (⁴F_7/2 → ⁴F_9/2) and (⁴I_11/2 → ⁴F_9/2) transitions, which increased the population of the ⁴F_9/2 level.     

Ce3+ induced broadband enhancement around 2 μm in Tm3+/Ho3+ co-doped tellurite glass

Tellurite glasses doped with Tm³⁺, Ho³⁺ and Ce³⁺ ions were prepared via melt-quenching to realise broadband and fluorescence enhancement in near-infrared (NIR) band. Under the pumping of a commercial 808 nm laser diode (LD), the emission bands at 2.0 μm, 1.85 μm, 1.47 μm, and 705 nm were observed in the Tm³⁺/Ho³⁺ co-doping glass samples, which originated from the transitions of Ho³⁺:⁵I₇→⁵I₈ and Tm³⁺:³F₄→³H₆, ³H₄→³F₄, ³F_2,3 → ³H₆, respectively. The existence of 2.0 μm band fluorescence is due to the energy transfer from the Tm³⁺:³F₄ level to the Ho³⁺:⁵I₇ level. This band overlaps with the 1.85 μm band which forms a broadband fluorescence spectrum in the range of 1600–2200 nm. In glass samples co-doped with Tm³⁺/Ho³⁺ with 0.085 mol% Ho₂O₃ and 1 mol% Tm₂O₃, the full width at half maximum (FWHM) of this broadband spectrum (1600–2200 nm) was as high as ∼370 nm. After introducing 0.6 mol% CeO₂, the emission intensity of broadband fluorescence increased by ∼50%, which was caused by the cross-relaxations between Ce³⁺ and Tm³⁺ ions. The lifetime of fluorescence decay was determined to prove the interactions among the doped rare-earth ions, the radiative parameters such as transition probability, branching ratio and radiative lifetime were calculated from the absorption spectra based on the Judd-Ofelt theory to better understand the observed luminescence phenomena. In addition, X-ray diffraction (XRD) confirmed the amorphous state structure of the synthesised glass samples, while Raman spectrum revealed the different vibrational structural units forming the glass network.     

Photoluminescent and electrical properties of novel Nd3+ doped ZnV2O6 and Zn2V2O7

Nd³⁺ doped ZnV₂O₆ and Zn₂V₂O₇ samples were synthetized by using melt-quenching method. X-ray diffraction patterns indicate that both samples are polycrystalline. The crystallinity was also verified by Raman scattering, from which the different vibrational modes of ZnV₂O₆ and Zn₂V₂O₇ were detected. Electron dispersive spectroscopy (EDS) analysis shows that the Nd³⁺ incorporation into the ZnV₂O₆ and Zn₂V₂O₇ hosts is around 0.9±0.1 and 0.2±0.1 at%, respectively. The micrographs obtained by Scanning Electron Microscopy, reveal that the Nd³⁺ doped ZnV₂O₆ sample is predominantly composed by micro-rods, whereas the Nd³⁺ doped Zn₂V₂O₇ one is only composed by irregular blocks. The band gap energies (E_g) were calculated from the diffuse reflectance spectra by the Kubelka–Munk equation; E_g values resulted to be 2.24 and 2.86 eV for the Nd³⁺ doped ZnV₂O₆ and Zn₂V₂O₇ samples, respectively. By means of two points dark conductivity measurements, conductivity values in the 10⁻⁴–10⁻⁶ and 10⁻⁶–10⁻⁸(Ω cm)⁻¹range for the Nd³⁺ doped ZnV₂O₆ and Zn₂V₂O₇ samples were measured, respectively. The conductivity as a function of the temperature indicated a semiconductor behavior. The photoluminescence spectra upon Ar⁺ laser excitation at 488 nm, exhibited the Nd³⁺ characteristics emissions. For instance, the Nd³⁺ doped ZnV₂O₆ sample displayed the Nd^{3+ 4}F_5/2→⁴I_9/2 and ⁴F_3/2→⁴I_9/2 emissions; while the Nd³⁺ doped Zn₂V₂O₇ one showed the Nd³⁺ characteristic emissions associated with the ⁴G_7/2, ⁴F_9/2, ⁴F_5/2 and ⁴F_3/2→⁴I_9/2 transitions. The lifetimes were 80 and 130 µs for the Nd³⁺ doped ZnV₂O₆ and Zn₂V₂O₇ samples, respectively. All these results suggest a successful synthesis of Nd³⁺ doped zinc vanadate compounds by the melt-quenching technique.     

Transparent Nd3+-Activated Glass-Ceramics in the Li2O–Al2O3–SiO2System: Physicochemical Aspects of Their Preparation and Optical Characteristics

The spectral–optical properties of transparent neodymium-activated lithium aluminosilicate glass-ceramics with titanium dioxide as a crystallization catalyst are investigated. The compositions of the initial glasses and the temperature–time schedules of heat treatment that provide a way of preparing highly homogeneous samples with low optical losses are determined. The most important parameters characterizing emission from the ⁴F_3/2metastable state of neodymium ions are obtained by analyzing the optical spectra of rare-earth ions in terms of the Judd–Ofelt theory. It is shown that the introduction of phosphorus oxide into the composition of glass-ceramics leads to a considerable increase in the stimulated emission cross section for the basic ⁴ F _3/2–⁴ I _11/2transition, even though the rare-earth activator is not incorporated into the crystalline phase. It is found that acceptable quantum yields of fluorescence with the retention of a high heat resistance of glass-ceramics can be achieved by decreasing the volume fraction of the crystalline phase. The lasing testing of the materials prepared is performed in a setup with a lamp pumping. The low lasing parameters can be associated with the specific features in the optical properties of glass-ceramics, primarily, with the revealed depolarization of polarized light due to the presence of microstresses at interfaces.     

The effect of Nd3+ concentration on fabrication,microstructure, and luminescent properties of anisotropic S-FAP ceramics

Nd³⁺ doped strontium fluorophosphate (S-FAP), with chemical formula Sr₅(PO₄)₃F, nanopowders were prepared using the co-precipitation method. The prepared powders had no impurity phase with a grain size of about 30 nm and the doping limit of Nd³⁺ ions in strontium fluorophosphate is about 9 at.%. The morphology and particle size were determined by the doping concentration of Nd³⁺. Anisotropic Nd: S-FAP transparent ceramics with different Nd³⁺ doping concentrations were fabricated successfully by the simple hot-pressing method. The grain size of prepared S-FAP transparent ceramics decreased first and then increased with the increase of Nd³⁺ concentration. The 2 at.% Nd: S-FAP ceramic presented the highest optical transmittance at all wavelengths range. The characteristic transitions from the ground state to the excited states of Nd³⁺ ions were observed from the absorption spectra, and the absorption cross-section was calculated at 3.71 × 10^–20 cm². The influence of Nd³⁺ ion concentration on luminescence intensity and fluorescence lifetime was studied under 796 nm excitation. The strong emission of ⁴F_3/2→⁴I_9/2 transition in Nd: S-FAP was calculated by Judd–Ofelt (J-O) theory.     

NIR photoluminescence and radioluminescence characteristics of Nd3+ doped BaTa2O6 phosphor

Barium tantalate phosphors activated with different concentrations of Nd³⁺ ion were synthesized via conventional solid state reaction method. The synthesized ceramic powders were characterized by X–ray diffraction (XRD), scanning electron microscopy‐energy dispersive spectroscopy (SEM‐EDS), laser diode (LD) excited near infrared (NIR) photoluminescence and X‐ray induced radioluminescence (RL) analyses. In XRD results, Nd³⁺ doped BaTa₂O₆ structure with tetragonal tungsten bronze (TTB) symmetry was observed to continue up to 10 mol%. In the examination of ceramic powders by SEM, grain size decreased with the increasing doping concentration. By using laser diode excited NIR photoluminescence of BaTa₂O₆:Nd³⁺ phosphor exhibited characteristic emissions at 877, 1080, and 1376 nm wavelengths due to ⁴F_3/2 → ⁴I_11/2, ⁴F_3/2 → ⁴I_11/2, and ⁴F_3/2 → ⁴I_11/2 band transitions respectively. Scintillation properties of Nd³⁺ doped samples from UV to near‐IR spectral region were carried out by the radioluminescence analysis. NIR and scintillation emissions initially increased by the doping concentration, and then decreased due to concentration quenching effect.     

Thermally enhanced near-infrared luminescence in CaSc2O4: Yb3+/Nd3+ nanorods for temperature sensing and photothermal conversion

Non-invasive photothermal therapy (PTT) is proposed as a powerful method for cancer treatment, in which a precise temperature monitoring is strongly recommended during the photothermal conversion process to prevent the damage of normal cells. Herein, ultra-sensitive optical thermometry with excellent resolution and outstanding light-to-heat conversion are simultaneously realized in CaSc₂O₄: Yb³⁺/Nd³⁺ nanorods. The temperature sensing of the nanorods is accomplished through fluorescence intensity ratio (FIR) technology based on the thermally coupled levels (TCLs) Nd³⁺: ⁴F_j (j = 7/2, 5/2, 3/2), of which the obtained absolute sensitivity is about 6.5 times larger than the optimal value of TCLs-based thermometers reported previously. Meanwhile, an intense thermal enhancement of Nd³⁺: ⁴F_j (j = 7/2, 5/2, 3/2) → ⁴I_9/2 transition is found due to the efficiency improvement of phonon-assisted energy transfer process between Yb³⁺ ions and Nd³⁺ ions. The penetrability of the near-infrared light emitting by Nd³⁺ ions is determined by a simple ex vivo experiment, indicating a penetration depth of 8 mm in the biological tissues with negligible effect on FIR values. Beyond that, the nanorods show remarkable photothermal conversion capacity under the excitation of 980 nm wavelength. The properties mentioned above show enormous potentiality of the present nanorods for PTT along with a real-time temperature sensing.     

Effect of neodymium ions on upconversion fluorescence studies of oxyfluorosilicate glasses for optoelectronic devices

Effect of Nd₂O₃ concentrations on optical properties and upconversion studies were investigated for oxyfluorosilicate glasses with composition of SiO₂-Al₂O₃-Na₂CO₃-SrF₂-CaF₂. The Judd-Ofelt (JO) intensity parameters, Ω_λ (λ = 2, 4 and 6) as well as radiative properties for the ⁴F_3/2 level of Nd³⁺ ion have been evaluated from the absorption spectra of 1.0 mol% Nd₂O₃-doped glass. For all the glass samples, the strong NIR emissions were observed at 891, 1058 and 1330 nm and have been attributed to ⁴F_3/2 → ⁴I_{9/2, 11/2, 13/2} transitions respectively. The stimulated emission cross-section for the ⁴F_3/2 → ⁴I_11/2 transition is evaluated and found to be 4.24 × 10^–20 cm². From the decay curves, experimental lifetimes (τ_exp) of the ⁴F_3/2 level have been determined and are found to be 363, 340, 205, 134, 122 and 54 μs for 0.1, 0.5, 1.0, 1.5, 2.0 and 3.0 mol% Nd³⁺ ions doped glasses, respectively. By exciting the prepared glass samples at 808 nm, the upconversion of infrared light into blue, green, yellow and red emission have also observed. These results indicate that the present glasses could be useful for opto-electric devices and solid state laser applications.     

Preparation and luminescence properties of Eu2O3 doped glass-ceramics containing NaY(MoO4)2

Eu₂O₃ doped transparent glass-ceramics containing NaY(MoO₄)₂ crystalline phase were prepared via melting-crystallization. The optimum heat treatment condition (660℃/3h) was determined by DSC, XRD, SEM and transmittance curves. The transmittance of glass-ceramic can reach 80 % in the visible region. The emission spectra of Eu₂O₃ doped glass-ceramics consist of Eu³⁺ ions characteristic emission peaks at 591nm (⁵D₀→⁷F₁) and 614nm (⁵D₀→⁷F₂). The optimal doping concentration of Eu₂O₃ in the glass-ceramics is 0.9 mol%, and fluorescence lifetime is 1.37042ms. The change of the ratio of red emission intensity to orange emission intensity leads to the shift of chromaticity coordinates from orange to red region, and the chromaticity coordinate (0.6337, 0.3635) of 0.9 mol% Eu₂O₃ doped glass-ceramic is closest to the standard red light coordinate. The results show that this kind of glass-ceramic is expected to be good red emission material.     

A new parameter for characterizing Eu3+ distribution in mixed-valence Eu-doped cubic LaF3-based transparent glass-ceramics

Mixed-valence Eu-doped transparent oxyfluoride glass-ceramics containing cubic LaF₃ nanocrystals were fabricated by traditional melt-quenching technique and consequent annealing processes. Their structural and luminescent properties were systemically investigated by X-ray diffraction (XRD), transmission electron microscopy, absorption, excitation, emission spectra, and fluorescence lifetime measurements. Analyses of XRD patterns prove that the new precipitated nanocrystals disperse in glass-ceramics crystallize in cubic LaF₃. The spectroscopic investigations show that Eu²⁺ ions have been incorporated into the LaF₃ nanocrystals preferentially, while Eu³⁺ ions still remain in the glass phase after crystallization. Based on the spectral results, a new parameter was defined to describe the changes of the environments of Eu³⁺ before and after crystallization more straightforwardly and more sensitively, where R_PG and R_GC represent the integrated intensity radio of ⁵D₀ → ⁷F₂ to ⁵D₀ → ⁷F₁ emissions of Eu³⁺ in PG and GC samples, respectively. Our investigation will not only enrich the understanding of fluoride nanocrystals-based oxyfluoride glass-ceramics, but also the distribution and luminescence behaviors of Eu³⁺ ions in them.     

Tailoring the efficient laser-absorption-melting behavior of Bi2O3-B2O3-ZnO-Nd2O3 glass for the OLED encapsulation

The efficient 810 nm laser energy conversion of glass frit had been proven to be the key to the long-term hermetic encapsulation of Organic Light Emitting Display (OLED). A direct laser energy conversion laser-assisted Bi₂O₃-B₂O₃-ZnO-Nd₂O₃ sealing glass material without extra laser absorbent such as carbon black, was designed and systematically investigated. The addition of Nd₂O₃, as glass modifiers with higher cationic field strength, could be conducive to enhancing the polymerization of glass network structure, manifesting that the glass-transition temperature Tg, onset-crystallization temperature Tc and thermal stability ΔT (ΔT = Tc-Tg) increased, while thermal expansion coefficient CTE dropped to 9.72×10⁻⁶/°C and advantageously matched with the glass substrate (8±1×10⁻⁶/°C). More importantly, the absorption rate of BBZ-Nd glass was more than 50 % between 800∼810 nm owing to the 4f-4f electron transition of Nd³⁺ ions, and yet the reflectivity and transmittance of the wavelength at 800–810 nm were lower. As optimal compositions, the addition of 3.0 wt% Nd₂O₃ in Bi₂O₃-B₂O₃-ZnO-Nd₂O₃ glass frit with higher absorption coefficients (80 %) led to instantaneous bonding encapsulation between glass substrates without interfacial cracks or pores with the 808 nm wavelength of the laser at 20 W and 2.4 mm/s.     

Heat-driven Tailored for Eliminating Nd3+ Re-clusters in Nd3+,Gd3+-codoped SrF2 Laser Ceramic

Transparent Nd³⁺,Gd³⁺-codoped SrF₂ laser ceramic was fabricated by a single-crystal ceramization (SCC) technique, and the fluorescence properties were also characterized. The results indicated that the SCC process would lead to reducing fluorescence properties of ceramic by re-clustering small amount of Nd³⁺ ions. In this study, the re-clustering of Nd³⁺ ions were addressed by a simple thermal drive-induced grains regrowth (TDIGR) treatment. The properties of the Nd³⁺,Gd³⁺-codoped SrF₂ laser ceramic undergo the TDIGR were improved and close to precursor Nd³⁺, Gd³⁺-codoped SrF₂ single crystal. Meanwhile, the transmittance of ceramic (T_{average@400-1400nm} ~ 92%) was hardly affected by the TDIGR treatment. Therefore, we have reasons to believe that the combination of SCC and TDIGR is a suitable approach to obtain high optical quality neodymium, buffer ion-codoped alkaline-earth fluoride (Nd³⁺,B³⁺-codoped MF₂) laser ceramics.     

Selective excitation in transparent oxyfluoride glass-ceramics doped with Nd3+

Transparent oxyfluoride nano-glass-ceramics have been prepared by melting-quenching and doped with five different Nd³⁺ concentrations (0.1–2 mol%) to obtain the most efficient ⁴F_3/2 → ⁴I_11/2,13/2 emission. It was observed by differential thermal analysis (DTA) that the addition of Nd³⁺ does not affect the crystallization mechanism which corresponds to a diffusion-controlled volumetric process that starts from a constant number of nuclei. Nevertheless, the presence of the dopant affects the kinetics due to the progressive increase of T_g on increasing the Nd³⁺ content. LaF₃ crystals with a size between 9 and 12 nm are obtained after heat treatments at T_g + 20–80 °C as confirmed by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HR-TEM). Energy dispersive X-ray (EDX) analysis shows the incorporation of Nd³⁺ ions into the LaF₃ nano-crystals. Judd-Ofelt analysis from the absorption spectra further demonstrate the incorporation of Nd³⁺ ions into the fluoride phase and the most relevant parameters such as radiative lifetime and stimulated emission cross-section are calculated. A detailed optical characterisation clearly shows that Nd³⁺ ions in the glass-ceramics are incorporated in both crystalline and amorphous phases. Low temperature site-selective emission and excitation spectra, together with the different lifetime values of the ⁴F_3/2 state depending on the excitation and emission wavelengths, allow emission from Nd³⁺ ions in the LaF₃ nanocrystals to be identified and correlated with the structural properties. As the Nd³⁺ concentration is increased beyond 0.1 mol%, a stronger quenching of lifetime is observed for Nd³⁺ ions residing in LaF₃ crystals than for those dispersed in the glass matrix. This strong concentration quenching is explained by the much higher concentration of Nd³⁺ ions in the crystalline phase with respect to that in the glass matrix.     

Sensitization effect of Nd3+ ions on Yb3+/Nd3+ co-doped oxyfluoride glasses and study of their optical,fluorescence, and upconversion abilities for visible laser and NIR amplifier applications

The development of laser technology has created intense demand for optical confinement materials with high performance. Herein the authors have been investigated Yb³⁺-singly doped and Yb³⁺/Nd³⁺-codoped SiO₂-based oxyfluoride glasses in terms of their optical absorption, and their near-infrared (NIR) and up-conversion (UC) emissions including emission decay profiles. Under 808 nm laser diode (LD) excitation, four NIR emission bands were observed i.e., (Nd³⁺: ⁴F_3/2 → ⁴I_9/2, Yb³⁺: ²F_5/2 → ²F_7/2, Nd³⁺: ⁴F_3/2 → ⁴I_11/2, and Nd³⁺: ⁴F_3/2 → ⁴I_13/2) in co-doped glasses. NIR emission cross-sections [(σ_emi) stimulated, (σ^M_emi) from Mc-cumber theory] were calculated for ²F_5/2 → ²F_7/2 (～1030 nm) transition of Yb³⁺ ion. σ_emi was found to be highest (26.27 × 10^?21 cm²) for the Yb³⁺: ²F_5/2 → ²F_7/2 transition in N2 glass. UC emission spectra recorded at 980 nm LD show bands centered at 500, 536, 595 & 610, and 664 nm, attributed to ⁴G_9/2 → ⁴I_9/2, ⁴G_7/2 → ⁴I_9/2& ⁴G_7/2 → ⁴I_11/2, ⁴G_5/2 → ⁴I_9/2, and ⁴G_9/2 → ⁴I_13/2 transitions, respectively. Decay profiles were analyzed for Yb³⁺: ²F_5/2 → ²F_7/2 (～1030 nm) and Nd³⁺: ⁴F_3/2 → ⁴I_11/2 (～1057 nm) transitions at 808 nm LD. Energy transfer (ET) process from Nd³⁺ to Yb³⁺ in present glasses were detailed.     

Multifunctional optical thermometry based on the stark sublevels of Er3+ in CaO-Y2O3: Yb3+/Er3+

A conventional high temperature solid state method was utilized to prepare CaO-Y₂O₃, which is a potential candidate for manufacturing crucible material to melt titanium and titanium alloys with low cost. Meanwhile, Yb³⁺ ions and Er³⁺ ions were selected as the sensitizers and activators respectively to dope into CaO-Y₂O₃, aimed at providing real-time optical thermometry during the preparation process of titanium alloys realized using fluorescence intensity ratio (FIR) technology. The results reveal that a high measurement precision can be acquired by using the Stark sublevels of Er^{3+ 4}F_9/2 to measure the temperature with a maximum absolute error of only about 3 K. In addition, by analyzing the dependence of ⁴I_13/2 → ⁴I_15/2 transition on pump power of 980 nm excitation wavelength, it was found that the laser-induced thermal effect has almost no influence on the temperature measurement conducted by using the FIR of the Stark sublevels of Er^{3+ 4}I_13/2, which means that a high excitation pump power can be used to obtain strong NIR emission and good signal-to-noise ratio for optical thermometry without the influence of the laser-induced thermal effect. All the results reveal that CaO-Y₂O₃: Yb³⁺/Er³⁺ is an excellent temperature sensing material with high measurement precision.     

Efficient energy transfer of Ce to Nd in SrF2 transparent ceramics for enhancing NIR emission

High optical quality Nd³⁺ and Ce³⁺ co-doped SrF₂ (Nd³⁺, Ce³⁺: SrF₂) transparent ceramics were fabricated successfully by a simple hot-pressing (HP) method. The phase composition, in-line transmittance, absorption and emission spectra, as well as the detailed energy transfer of Nd³⁺ and Ce³⁺ were investigated. In addition, the Judd- Ofelt (J-O) theory was adopted to evaluate the luminescence property. The SrF₂ transparent ceramic samples exhibited excellent optical properties, up to 82 % at 400 nm and 92.5 % at 1054 nm. The fracture surface of SrF₂ transparent ceramic proved nearly dense microstructure and EDS results demonstrated uniform doping. The addition of cerium ions changed the crystal field environment of neodymium ions and shifted the emission peak to higher wavelengths at 796 nm excitation. Moreover, through the energy transfer process of Ce³⁺ to Nd³⁺, the occurrence of concentration quenching phenomenon was avoided under 298 nm excitation, and the emission cross-section of ⁴F_3/2→⁴I_11/2 increased to 3.1 × 10⁻²⁰ cm².     

Improved broadband near-infrared luminescence in Nd3+/Tm3+ co-doping tellurite glass with Ag NPs

The near-infrared (NIR) luminescence in S+E+O bands of tellurite glasses doped with Nd³⁺/Tm³⁺ and Ag nanoparticles (NPs) was investigated. The tellurite glasses were prepared by melt-quenching and heat-treated techniques. Under the excitation of 808 nm laser, Nd³⁺/Tm³⁺ doped tellurite glasses produced three NIR luminescence bands of 1.33, 1.47 and 1.85 μm, originating from Nd³⁺:⁴F_3/2→⁴I_13/2, Tm³⁺:³H₄→³F₄ and Tm³⁺:³F₄→³H₆ transitions respectively. Interestingly, a broadband luminescence spectrum ranging from 1280 to 1550 nm with the FWHM (full width at half maximum) about 201 nm was obtained due to the overlapping of the first two NIR bands. Further, the peak intensity of this broadband luminescence was increased by 75% after the introduction of Ag NPs with diameter in 10–20 nm. The analysis of fluorescence decay shows that compared with the enhanced local electric field, the energy transfer from Ag species to Nd³⁺ and Tm³⁺ ions plays a major role in luminescence enhancement. The findings in this work indicate that tellurite glass co-doped with Nd³⁺/Tm³⁺ and Ag NPs is a potential gain material applied in the S+E+O-band photonic devices.     

Preparation and luminescence of Dy3+/Tm3+ co-doped Ca3NbGa3Si2O14 glass-ceramics for w-LED

In this work, a series of Dy³⁺ and Dy³⁺/Tm³⁺ ion activated Ca₃NbGa₃Si₂O₁₄ glass-ceramics were prepared by traditional melt crystallization method, and report on the structural, optical, and energy transfer (ET)-based photoluminescence (PL) properties of glass-ceramics co-doped Dy³⁺/Tm³⁺. The preparation of glass-ceramics was studied by DTA, XRD, SEM, and UV–vis photometer technology, phase composition, transmittance, optimum heat treatment conditions, and luminescence properties. The best heat treatment procedure for obtaining transparent and well-formed glass-ceramics is crystallization at 820 °C for 5 h. The spectra excited by Tm³⁺ and Dy³⁺ have intersections at 352 nm and 365 nm, which means that CNGS: Dy³⁺/Tm³⁺ can be effectively excited by 352 nm and 365 nm ultraviolet light. Under the excitation of 352 nm ultraviolet light, four main emission peaks corresponding to ¹D₂ →³F₄, ⁴F_9/2 → ⁶H_15/2, ⁴F_9/2 → ⁶H_13/2, ⁴F_9/2 → ⁶H_11/2 were found at 456 nm, 484 nm, 577 nm, and 663 nm, respectively. When the optimal concentration (4 at.%) of Dy³⁺ is Co-doped with a different amount of Tm³⁺, the luminous color can be adjusted by adjusting the doping amount of Tm³⁺ and changing the excitation wavelength. There is an overlapping region between the emission spectrum of Tm³⁺ doped glass and the excitation spectrum of Dy³⁺ doped glass, which indicates that there is energy transfer between Tm³⁺ and Dy³⁺. In addition, CNGS: Dy³⁺/Tm³⁺ CIE coordinates show that the color coordinates (0.3324, 0.3352) when y = 0.02 under 365 nm excitation are closest to the standard white light (0.333, 0.333), indicating that this glass has potential applications in WLED devices.     

Structural,optical, and spectroscopic properties of Er3+-doped TeO2–ZnO–ZnF2 glass-ceramics

Transparent fluorotellurite glass-ceramics have been obtained by heat treatment of precursor Er-doped TeO₂–ZnO–ZnF₂ glasses. ErF₃ nanocrystals nucleated in the glass-ceramics have a typical size of 45 ± 10 nm. Based on the Judd-Ofelt theory, the main radiative parameters for the ⁴I_13/2 → ⁴I_15/2 transition have been obtained. The split of the absorption and emission bands and the reduction of the Ω₂ parameter, as compared to the glass, confirm the presence of Er³⁺ ions in a crystalline environment in glass-ceramic samples. The analysis of the ⁴I_13/2 decays suggests that a fraction of Er³⁺ ions remains in a glass environment while the rest forms nanocrystals. For the glass-ceramics, intense red and green upconversion emissions were observed with an enhancement of the ⁴F_9/2 → ⁴I_15/2 red one compared to the glass sample. The temporal evolution of the red emission together with the excitation upconversion spectra suggests that energy transfer processes are responsible for the enhancement of the red emission.