Synthesis and characterization of holmium oxide doped cadmium lead borate glasses

Holmium doped cadmium lead borate glasses were prepared from melting in appropriate proportions of a mixture of CdO, PbO₂, H₃BO₃ and (1–2 mol %) Ho₂O₃ in the temperature range of 800–850 °C. The density of glass samples was measured using Archimedes Principle. The infrared spectra of the glasses in the range of 400–4000 cm^?1 showed their structure systematically. No boroxol ring formation was observed in the structure of these glasses, but the conversion of 3-fold to 4-fold coordination of boron atoms in the structure of glasses was observed. The glass transition studies were done through differential scanning calorimetry. The optical analysis is done by using the Judd–Ofelt theory.     

Preparation and luminescence of water soluble poly (N-vinyl-2-pyrrolidone)/LaF3:Eu nanocrystals

Lanthanide-doped luminescent nanocrystals have great potential as biological luminescent labels, but their use has been limited because of most of these nanocrystals are hydrophobic. In this work, water soluble LaF₃:Eu³⁺ down-conversion nanocrystals were prepared by encapsulated individual nanocrystals with polyvinylpyrrolidone (PVP). Their morphology, surface structure and luminescence properties were explored in detail. The results indicate that these nanocrystals can be readily dispersed in water, forming a stable and transparent colloidal solution. The colloidal solution displayed unique red luminescence with high emission intensity under ultraviolet excitation. These results suggest that these nanocrystals have great potential as luminescent labeling materials for biological applications.     

Optical properties of Sm-doped CaF2 bismuth borate glasses

Sm³⁺-doped calcium fluoride bismuth borate glasses were prepared and characterized optically and the oscillator strengths and Judd–Ofelt parameters for the glass containing 1.5 mol% of Sm₂O₃ were calculated. Density and optical absorption, transmission and the emission spectra were measured. The values of Judd–Ofelt parameters suggested an increase in the degree of asymmetry the local ligand field at Sm³⁺ sites. The optical band gap energy, band tailing parameter and Urbach's energy were calculated for all glass samples. It was found that with increasing the concentration of Sm₂O₃ content the values of the optical band gap energy decrease whereas Urbach's energy increases. Absorption and excitation spectra indicate that commercial UV and blue laser diodes, blue and bluish-green LEDs and Ar⁺ optical laser are powerful excitation sources for Sm³⁺ visible fluorescence in the glass.     

Synthesis of NaYF4 nanocrystals doped with Yb/Er and influence of citric acid on the green and red luminescence

In this paper, NaYF₄ nanocrystals doped with Yb³⁺ and Er³⁺ were synthesized in a medium containing polyethylene glycol and citric acid. This nanocrystal presents up-converting green and red emission bands which were simultaneously observed under the excitation of a 980 infrared diode laser. Mainly, the green to red ratio (GRR) of the up-conversion emission of the hexagonal NaYF₄ nanocrystals doped with Yb³⁺ and Er³⁺ can be finely tuned by changing the content of citric acid to be nearly an arithmetic progression, i.e. 6/4, 5/4, 4/4, and 3/4. The further analysis revealed that citric acid plays a key role in improving the surface crystallinity of NaYF₄ nanocrystals doped with Yb³⁺ and Er³⁺, to which the achievement of fine controlling on GRR is ascribed.     

Upconversion luminescence of Er/Yb-codoped natrium-germanium-bismuth glasses

The absorption and upconversion fluorescence spectra of a series of Er³⁺/Yb³⁺-codoped natrium-germanium-bismuth glasses have been studied. The transition probabilities, excited state lifetimes, and the branching ratios have been predicted for Er³⁺ based on the Judd-Ofelt theory. At room temperature, an upconversion efficiency of 6.1×10⁻² has been obtained for the green emission from the glass with 0.5 wt% Er₂O₃ and 3.0 wt% Yb₂O₃ pumped by 980 nm radiation with an intensity of 270 W/cm². And the “standardized” efficiency for green upconversion light is higher than that reported in lead-germanate, lead-tellurite-germanate, and silicate glasses. The results indicate that the Er³⁺/Yb³⁺-codoped natrium-germanium-bismuth oxide glass may be a potential material for developing upconversion optic devices.     

Role of Al coordination in barium phosphate glasses on the emission features of Ho ion in the visible and IR spectral ranges

The glasses of the composition (39−x)BaO-xAl₂O₃-60P₂O₅:1.0Ho₂O₃ (in mol%) with x value ranging from 1.0 to 4.0 have been synthesized. The IR spectral studies of these glasses have indicated that there is a gradual transformation of Al³⁺ ions from tetrahedral to octahedral with increase in the concentration of Al₂O₃ up to 3.0 mol%. Optical absorption and fluorescence spectra (in the visible and NIR regions) of these glasses have been recorded at room temperature. The Judd-Ofelt theory could successfully be applied to characterize the absorption and luminescence spectra of Ho³⁺ ions in these glasses. From the luminescence spectra, various radiative properties like transition probability A, branching ratio β_r, the radiative lifetime τ_r and emission cross-section σ^E for various emission levels of these glasses have been evaluated. The radiative lifetime of the ⁵S₂→⁵I₈ (green emission) transition has also been measured. The variations observed in these parameters have been discussed in the light of varying co-ordinations (tetrahedral and octahedral positions) of Al³⁺ ions in the glass network. The influence of hydroxyl groups on the luminescence efficiency of the transition ⁵S₂→⁵I₈ has also been discussed. Finally the optimum concentration of Al₂O₃ for getting maximum luminescence output has also been identified and reported.     

Investigation of energy transfer and frequency upconversion in Ho/Yb co-doped tellurite glasses

A serials of Ho³⁺/Yb³⁺ co-doped tellurite glasses by pumping 970 nm laser diode (LD) were demonstrated to obtain a high efficiency of infrared-to-visible upconversion. Two intense emission bands were observed in Ho³⁺/Yb³⁺ co-doped tellurite glasses centered at 549 and 664 nm corresponding to Ho³⁺: ⁵S₂(⁵F₄)→⁵I₈ and ⁵F₅→⁵I₈ transitions, respectively. The upconversion intensities of red and green emissions in Ho³⁺/Yb³⁺ co-doped glasses were enhanced largely when increasing Yb₂O₃ content. The dependence of upconversion intensities on excitation power and the possible upconversion mechanisms had been evaluated by a proper rate equation model. The energy transfer coefficients were estimated by fitting the simulated curves to the measured ones. The obtained three energy transfer coefficients C_D2, C_D3 and C_D4 were C_D2=5.0×10⁻¹⁸ cm³/s, C_D3=1.5×10⁻¹⁷ cm³/s, C_D4=9.0×10⁻¹⁷ cm³/s.     

Raman studies and optical properties of some (PbO)x(Bi2O3)0.2(B2O3)0.8−x glasses

Five (PbO)_x(Bi₂O₃)_0.2(B₂O₃)_0.8−x glasses, where x = 0, 0.2, 0.3, 0.4 and 0.6, were prepared. The dilatometric glass transition temperature (T_g) was found in the region 470 (x = 0)≥ T_g ( °C) ≥ 347 (x = 0.6), and the density (ρ) varied within 4.57 (x = 0) ≤ ρ (g/cm³) ≤ 8.31 (x = 0.6). Raman spectra indicated the conversion of BO₃ to BO₄ entities for low x values but for x > 0.3, namely, for x → 0.6, back‐conversion occurred, most probably. From the measurements of the optical transmission on very thin bulk samples, the room temperature optical gap values (E_g) were determined to be in the range 4.03 (x = 0)≥ E_g (eV) ≥ 3.08 (x = 0.6). The temperature (T) dependence of the optical gap (E_g(T)) in the region 300 ≤ T(K) ≤ 600 was examined and approximated by a linear relationship of the form of E_g(T) = E_g(0)− γT, where γ × 10⁻⁴(eV/K) varied from 5.1 to 6.8. The non‐linear refractive index (n₂) was estimated from the optical gap values and it was found to correspond to the n₂ values calculated from the experimental third‐order non‐linear optical susceptibility taken from the literature. Copyright © 2008 John Wiley & Sons, Ltd.     

Optical properties of Er in MoO3-Bi2O3-TeO2 glasses

Erbium-doped MoO₃−Bi₂O₃−TeO₂ (MBT) glasses suitable for broadband optical amplifier applications have been fabricated and characterized optically. The maximum phonon band of undoped glasses is at 915 cm⁻¹, and the emission from the Er³⁺: ⁴I_13/2 → ⁴I_15/2 transition locates around 1.53 μm with a full width at half maximum (FWHM) of ∼80 nm. The lifetime and quantum efficiency of the ⁴I_13/2 level are 2.13 ms and ∼90%, respectively. Under the same measurement condition, the upconversion emission intensities at 550 nm in Er³⁺-doped MBT glasses is about 30 times weaker than that in Er³⁺-doped Na₂O−ZnO−TeO₂ (NZT) glasses.     

Luminescence and laser transition studies of Dy:K-Mg-Al fluorophosphate glasses

Dysprosium ion doped fluorophosphate glasses with compositions of PKMAFDy: (56−x/2) P₂O₅+17K₂O+8Al₂O₃+(15−x/2)MgO+4AlF₃+xDy₂O₃ (x=0.01, 0.05, 0.1, 1.0 and 2.0 mol%) have been prepared by melt quenching technique and are characterized by optical absorption, emission spectra and fluorescence lifetime measurements. The observed bands in the absorption spectrum are analysed by using free-ion Hamiltonian (H_FI) model. The Judd-Ofelt (JO) analysis has been performed and the intensity parameters (Ω_λ, λ=2, 4, 6) have been evaluated that are used to predict radiative properties. From emission spectra, the effective bandwidth (Δλ_eff) and the stimulated emission cross-section (σ(λ_p)) were evaluated. The fluorescence decay from the ⁴F_9/2 level of Dy³⁺ ions have been measured by monitoring the intense ⁴F_9/2→⁶H_13/2 transition (573 nm). The lifetimes (τ) are found to decrease with increasing concentration due to concentration quenching. The decay curves are single exponential for lower concentrations and gradually changes to non-exponential for higher concentrations. The non-exponential decay curves are well fitted to the Inokuti-Hirayama (IH) model for S=6 which indicates that the energy transfer between the donor and acceptor is of dipole-dipole type. The systematic analysis on decay measurements reveals that the energy transfer mechanism strongly depends on concentration as well as glass composition.     

Optical properties of lithium magnesium borate glasses doped with Dy and Sm ions

Several studies showed the interesting properties of trivalent lanthanide ions when doped in various types of glasses. Optical and physical properties of lithium magnesium borate glasses doped with Dy³⁺ then with Sm³⁺ ions were determined by measuring their absorption and luminescence spectra in the visible region. The absorption spectra of Dy³⁺ showed eight absorption bands with hypersensitive transition at 1265 nm (⁶H_15/2→⁶F_11/2-⁶H_9/2) and three PL emission bands at 588 nm (⁴F_9/2→⁶H_15/2), 660 nm (⁴F_9/2→⁶H_13/2) and 775 nm (⁴F_9/2→⁶H_11/2). Regarding the Sm3⁺, nine absorption bands were observed with hypersensitive transition at 1237 nm (⁶H_5/2–⁶F_7/2); the PL spectrum showed four prominent peaks at ⁴G_5/2→⁶H_5/2 (yellow color), ⁴G_5/2→⁶H_7/2 (bright orange color), ⁴G_5/2→⁶H_9/2 (orange reddish color) and ⁴G_5/2→⁶H_11/2 (red color), respectively. Finally, a series of physical parameters such as the oscillator strengths, refractive index, ions concentration, Polaron radius and other parameters were calculated for each dopant.     

Optical properties of vanadium-doped bismuth borate glasses before and after gamma-ray irradiation

UV–visible, infrared and Raman spectra, together with thermal properties, were measured for glasses from the system Bi₂O₃–B₂O₃–V₂O₅ before and after successive gamma irradiations. The UV–visible spectrum of the undoped glass before irradiation reveals five UV bands at 210, 275, 310, 350 nm, an intense band at 380 nm and a visible band at 420 nm due to the possible combined presence of trace iron impurities and Bi³⁺ ions. The V-doped glasses reveal six UV bands and two visible bands, probably arising from vanadium ions in three possible valencies, V³⁺, V⁴⁺ and V⁵⁺, beside that due to trace iron impurity beside Bi³⁺ ions. The spectra reveal an obvious resistance of the glasses to successive gamma irradiation. The Raman and infrared spectra show characteristic absorption bands, which indicate the sharing of Bi³⁺ ions as glass-forming (BiO₆) octahedral units together with the presence of various groups of the borate network.     

Energy transfer and infrared-to-visible upconversion luminescence of Er/Yb-codoped halide modified tellurite glasses

We report on the energy transfer and frequency upconversion spectroscopic properties of Er³⁺-doped and Er³⁺/Yb³⁺-codoped TeO₂-ZnO-Na₂O-PbCl₂ halide modified tellurite glasses upon excitation with 808 and 978 nm laser diode. Three intense emissions centered at around 529, 546 and 657 nm, alongwith a very weak blue emission at 410 nm have clearly been observed for the Er³⁺/Yb³⁺-codoped halide modified tellurite glasses upon excitation at 978 nm and the involved mechanisms are explained. The quadratic dependence of fluorescence on excitation laser power confirms the fact that the two-photon contribute to the infrared to green-red upconversion emissions. And the blue upconversion at 410 nm involved a sequential three-photon absorption process.     

Temperature dependence of impurity quenched luminescence in Tm:LiLuF4

The study of the optical properties of a LiLuF₄ crystal doped with Tm³⁺ yielded the discovery of a strong temperature dependence of the Tm-Tm diffusion coefficient. Spectroscopic characteristics have been investigated as a function of the sample temperature, with particular regard to the luminescence decay following pulsed excitation. An appreciable excitation of the lifetime of the ³F₄ manifold is observed over the temperature range 8.9-298 K. The Judd-Ofelt calculations point out a radiative lifetime considerably longer than the experimental one. These facts suggest a theoretical interpretation based on the presence of impurities that quench the manifold and on a temperature-dependent energy migration between Tm³⁺ ions. A one-parameter best fit of the experimental measurements strongly confirms this hypothesis. Weak OH⁻ ion concentration is detected by means of IR and UV spectra, thus supporting the theoretical interpretation.     

Infrared luminescence from spark-processed silicon

The infrared (IR) photoluminescence (PL) emission of spark-processed silicon (sp-Si) was investigated. A broad and strong room temperature PL peak in the 945 nm (1.31 eV) spectral range was observed when sp-Si was excited with an argon laser. This peak is different from the PL commonly reported for anodically etched porous silicon and other silicon-based materials. The PL intensity increases substantially after annealing sp-Si between 350 and 500 °C in air after which it decreases again. The PL wavelength is observed to peak at 1010 nm by annealing sp-Si near 450 °C. It was further found that the most efficient PL occurs for a Si/O ratio of 0.3, for a small spark gap of about 1 mm, and for spark-processing times in the 15-60 min range.A model for the IR PL is proposed which mirrors that for visible PL. Specifically, it is proposed that the electrons which have been pumped by the laser from the ground state into a broad quasi-absorption band (or closely spaced absorption lines between 1.7 and 2.3 eV) revert back to lower IR levels at 1.31 eV by a non-radiative transition from where they revert radiatively to the ground state by emitting the observed 945 nm light.     

Luminescent studies of Dy ion in alkali lead tellurofluoroborate glasses

Dy³⁺-doped alkali lead tellurofluoroborate (RLTB) glasses (R=Li, Na and K) were prepared by melt quenching technique. Judd-Ofelt theory has been used to evaluate the three intensity parameters Ω₂, Ω₄ and Ω₆ from the experimental oscillator strengths. The photoluminescence spectra obtained by the excitation wavelength of 385 nm show four emission bands at 454, 483, 575 and 665 nm corresponding to the ⁴I_15/2→⁶H_15/2 and ⁴F_9/2→⁶H_J/2 (J=15/2, 13/2 and 11/2) transitions, respectively. The laser characteristic parameters like fullwidth at half maxima (FWHM), stimulated emission cross-sections (σ_e), optical gain parameters (σ_e×τ_exp) and gain bandwidth parameters (σ_e×FWHM) were determined. From the visible emission spectra, yellow to blue (Y/B) intensity ratios and chromaticity coordinates were also estimated. The lifetimes of ⁴F_9/2 metastable state were also measured and discussed.     

Er3+掺杂重金属氧氟硅酸盐玻璃的上转换发光研究

研究了Er3 掺杂重金属氧氟硅酸盐玻璃的吸收光谱、上转换光谱和拉曼光谱 ,分析了重金属氧氟硅酸盐玻璃中Er3 的上转换发光机理 .结果表明 :通过 975nm的激光二极管激发 ,在室温下同时观察到蓝光 (4 1 1nmj)、绿光(5 2 5和 5 4 3nm)和红光 (6 5 5nm) ,分别是由于Er3 离子2 H9 2 →4 I1 5 2 ,2 H1 1 2 →4 I1 5 2 ,4 S3 2 →4 I1 5 2 ,和4 F9 2 →4 I1 5 2 跃迁 .随Er2 O3浓度的增加 ,蓝光、绿光和红光的发光强度都增强 ,上转换发光机理主要涉及能量转移和激发态吸收 ,强烈的绿光和红光激发是由于双光子吸收过程 ,而微弱的蓝光是由于三光子吸收过程 .拉曼光谱发现 ,对Er3 离子在重金属氧氟硅酸盐玻璃中的上转换发光 ,玻璃结构中的PbF2 起到重要作用     

Tm3+/Yb3+共掺氧卤碲酸盐玻璃上转换发光研究

研究了Tm³⁺/Yb³⁺共掺氧卤碲酸盐玻璃的上转换发光光谱，分析了Tm₂O₃含量对Tm³⁺/Yb³⁺共掺氧卤碲酸盐玻璃上转换发光的影响机理.结果表明：在Tm³⁺/Yb³⁺共掺氧卤碲酸盐玻璃的上转换发光中，Tm³⁺存在较强的浓度猝灭效应.随Tm₂O₃含量增加，Tm³⁺的上转换蓝光和红光强度先增加，后降低，在0.1mol% Tm₂O₃达到最大.该结果有助于进一步提高Tm³⁺的上转换发光效率.