Emission features of Ho ion in Nb2O5, Ta2O5 and La2O3 mixed Li2O-ZrO2-SiO2 glasses

Li₂O-ZrO₂-SiO₂: Ho³⁺ glasses mixed with three interesting d-block elemental oxides, viz., Nb₂O₅, Ta₂O₅ and La₂O₃, were prepared. Optical absorption and photoluminescence spectra of these glasses have been recorded at room temperature. The luminescence spectra of Nb₂O₅ and Ta₂O₅ mixed Li₂O-ZrO₂-SiO₂ glasses (free of Ho³⁺ ions) have also exhibited broad emission band in the blue region. This band is attributed to radiative recombination of self-trapped excitons (STEs) localized on substitutionally positioned octahedral Ta⁵⁺ and Nb⁵⁺ ions in the glass network. The Judd-Ofelt theory was successfully applied to characterize Ho³⁺ spectra of all the three glasses. From this theory various radiative properties, like transition probability A, branching ratio β_r and the radiative lifetime τ_r, for ⁵S₂ emission levels in the spectra of these glasses have been evaluated. The radiative lifetime for ⁵S₂ level of Ho³⁺ ions has also been measured and quantum efficiencies were estimated. Among the three glasses studied the La₂O₃ mixed glass exhibited the highest quantum efficiency. The reasons for such higher value have been discussed based on the relationship between the structural modifications taking place around the Ho³⁺ ions.     

Investigation on spectral features of tungsten ions in PbO-Bi2O3-As2O3 glass matrix

Lead bismuth arsenate glasses mixed with different concentrations of WO₃ (ranging from 0 to 6.0 mol%) were synthesized. Differential thermal analysis (DTA), optical absorption, ESR and IR spectral studies have been carried out. The results of DTA have indicated that there is a gradual decrease in the resistance of the glass against devitrification with increase in the concentration of WO₃ upto 4.0 mol%.The optical absorption spectra of these glasses exhibited a relatively broad band peaking at about 880 nm identified due to d_xy→d_x²_−y² transition of W⁵⁺ ions; this band is observed to be more intense in the spectrum of glass containing 4.0 mol% of WO₃. Further, two prominent kinks attributed to ³P₀→¹S₀, ¹D₂ transitions of Bi³⁺ ions have also been located in the absorption spectra. The ESR spectra of these glasses recorded at room temperature exhibited an asymmetric signal at g_⊥∼1.71 and g_ll∼1.61. The intensity of the signal is observed to be maximal for the spectrum of the glass W₄. The quantitative analysis of optical absorption and ESR spectral studies have indicated that there is a maximum reduction of tungsten ions from W⁶⁺ state to W⁵⁺ state in the glass containing 4.0 mol% of WO₃. The IR spectral studies have indicated that there is a increasing degree of disorder in the glass network with increase in the concentration of WO₃ upto 4.0 mol%.     

Fluorescence features of Sm ions in Na2SO4-MO-P2O5 glass system—Influence of modifier oxide

Na₂SO₄-P₂O₅:Sm³⁺ glasses mixed with three different alkaline earth modifier oxides viz., MgO, CaO and BaO were prepared. Optical absorption and photoluminescence spectra of these glasses have been recorded at room temperature; the Judd-Ofelt theory was successfully applied to characterize these spectra. From this theory, various radiative properties like transition probability A, branching ratio β_r, the radiative lifetime τ_r, for various emission levels in the spectra of these glasses have been determined and reported. An attempt has also been made to throw some light on the relationship between the structural modifications and luminescence efficiencies in the change of scenario for modifying oxides in the glass network.     

Effect of Li2O content on physical and structural properties of vanadyl doped alkali zinc borate glasses

The effect of Li₂O content in vanadyl doped 20ZnO+xLi₂O+(30−x)Na₂O+50B₂O₃ (5≤x≥25) glasses has been studied with respect to their physical and structural properties. The absence of sharp peaks in XRD spectra of these glass samples confirms the amorphous nature. The physical parameters like density, refractive index, ionic concentration and electronic polarizability vary non-linearly with x mol% depending on the diffusivities of alkali ions. EPR and optical absorption spectra reveal that the resonance signals are characteristics of VO²⁺ ions in tetragonally compressed octahedral site. Spin-Hamiltonian, crystal field, tetragonal field and bonding parameters are found to be in good agreement with the other reported glass systems. The tetragonal distortion (g_⊥-g_∥) and Dt reveals that their values vary non-linearly with Li₂O content and reaches a minimum at x=10 mol%. An anomaly of character has been observed in all the properties of vanadyl doped glass systems, which gives a clear indication of mixed alkali effect.     

Effect of CuO addition on the optical and electrical properties of sodium zinc borophosphate glasses

Sodium borophosphate glasses doped with copper ions having general composition 20Na₂O-20ZnO-25B₂O₃-(35-x) P₂O₅-x CuO (x=1-8 mol %) were prepared using conventional melt-quench method and characterized by density, UV-visible optical absorption, photoluminescence and conductivity measurements. E_optical values for different glass samples are found to decrease systematically from 3.5 to 2.5 eV with increase in CuO content in the glass. Network modifying action of CuO with the glass network has been confirmed from the UV-visible optical absorption studies. Presence of Copper in the form of Cu⁺ species has been confirmed from photoluminescence measurements. The electrical conductivity (σ) increases with increase in copper oxide content in the glass and temperature dependence of electrical conductivity confirmed the semiconducting nature of the samples.     

Spectral studies on Cu ions in sodium–lead borophosphate glasses

Electron Paramagnetic Resonance (EPR) and optical absorption spectra of Cu²⁺ ions in sodium–lead borophosphate glasses doped with different concentrations of Cu²⁺ ions have been studied. EPR spectra of all the glass samples exhibit resonance signals characteristic of Cu²⁺ ions. The values of spin-Hamiltonian parameters indicate that the Cu²⁺ ions in sodium–lead borophosphate glasses are present in octahedral sites with tetragonal distortion. The optical absorption spectra of all the glass samples show a single broad band, which has been assigned to the ²B_1g→²B_2g transition of Cu²⁺ ions. The optical band gap energy (E_opt) and Urbach energy (ΔE) are calculated from their ultraviolet absorption edges. The emission bands observed in the ultraviolet and blue region are attributed to 3d⁹4s→3d¹⁰ triplet transition in Cu⁺ ion. The FT-IR spectra show that the glass system contains BO₃, BO₄ and PO₄ structural units.     

Optical absorption and thermoluminescence studies on LiF-Sb2O3-B2O3 glasses doped with Ni ions

20LiF-(30−x)Sb₂O₃-50B₂O₃:xNiO glasses with the value of x (ranging from 0 to 1.0 mol% in steps of 0.2) were prepared. A number of studies, viz. differential scanning calorimetry, optical absorption, magnetic susceptibility and thermoluminescence, on these glasses were carried out as a function of nickel ion concentration. An anomaly has been observed in all the properties of these glasses when NiO concentration is about 0.6 mol%. The results of these studies were analysed in the light of different environments of nickel ions in the glass network.     

Spectral studies on Mn ions doped in sodium-lead borophosphate glasses

Electron paramagnetic resonance (EPR), optical absorption, and luminescence spectral studies of Mn²⁺ ions doped in (30−x) (NaPO₃)₆+30PbO+40B₂O₃+xMnO₂ (x=1.0, 2.0, 3.0, 4.0, and 5.0 mol%) glasses have been studied. The EPR spectra exhibit resonance signals with effective g value at g_eff≈2.02 with six line hyperfine structure. A weak resonance signal with effective g value at g_eff≈4.3 is also observed for higher concentrations of Mn²⁺ ions. The EPR spectra of x =3.0 mol% of Mn²⁺ in sodium-lead borophosphate glass sample have been studied at various temperatures. It is observed that the resonance signal intensity decreases with increase in temperature. The optical absorption spectrum exhibits bands characteristic of Mn²⁺ ions in octahedral symmetry. From the analysis of the bands, the crystal-field parameter Dq and the Racah interelectronic repulsion parameters B and C have been evaluated. The emission spectrum exhibits single broad band in the green region.     

Spectral studies on Cr ions doped in sodium-lead borophosphate glasses

Electron paramagnetic resonance (EPR), optical absorption and emission spectra of Cr³⁺ ions doped in (30−x) (NaPO₃)₆+30PbO+40B₂O₃+xCr₂O₃ (x=0.5, 2.0, 3.0, 4.0 and 5.0 mol%) glasses have been studied. The EPR spectra exhibit resonance signals with effective g values at g≈4.55 and g≈1.97. The EPR spectra of x=3.0 mol% of Cr₂O₃ in sodium-lead borophosphate glass sample were studied at various temperatures (295-123 K). The intensity of the resonance signals increases with decrease in temperature. The optical absorption spectrum exhibits four bands characteristic of Cr³⁺ ions in octahedral symmetry. From the analysis of the bands, the crystal-field parameter Dq and the Racah interelectronic repulsion parameters B and C have been evaluated. The emission spectrum exhibit one broad band characteristic of Cr³⁺ ions in octahedral symmetry. This band has been assigned to the transition ⁴T_2g (F)→⁴A_2g (F). Correlating EPR and optical data, the molecular bonding coefficient (α) has been evaluated.     

Influence of ligand coordination of cobalt ions on structural properties of ZnO-ZnF2-B2O3 glass system by means of spectroscopic studies

The glasses of the composition 10ZnO-30ZnF₂-60B₂O₃ doped with different concentrations of CoO were prepared. Differential scanning calorimetric (DSC) studies, optical absorption, photoluminescence and infrared spectra of these glasses have been carried out. DSC studies have indicated that the resistance of the glass against devitrification increases with the increase in the concentration of CoO. Optical absorption spectra have exhibited one octahedral band due to ⁴T_1g(F)→²T_1g(H) and two tetrahedral bands due to ⁴A₂(⁴F)→⁴T₁(⁴P) ⁴A₂(⁴F)→⁴T₁(⁴F) transitions of Co²⁺ ions at about 525, 570 and 1400 nm, respectively. As the concentration of CoO is increased the tetrahedral bands are observed to grow at the expense of octahedral band. The luminescence spectra have exhibited two emission bands in the spectral regions of 600-700 nm and 800-900 nm due to ⁴T₁(⁴P)→⁴A₂(⁴F) and ⁴T₁(⁴P)→⁴T₂(⁴F) tetrahedral transitions of Co²⁺ ions, respectively. With the increasing content of cobalt ions in the glass matrix, the half width and intensity of these bands are observed to increase. The analysis of the results of these two spectra coupled with IR spectra has indicated that as the concentration of CoO is increased in the glass matrix, the tetrahedral occupancy of cobalt ions dominates over the octahedral occupancy and increase the rigidity of the glass network.     

Physical and Spectral Investigations of Cu<Superscript>2+</Superscript>-Doped Alkali Zinc Borate Glasses

Physical and spectral studies on 20ZnO + xLi₂O + (30-x)Na₂O + 50B₂O₃ (5 ≤ x ≥ 25) doped with 0.1 mol% of paramagnetic CuO impurity are carried out. Powder X-ray diffraction patterns of the glass samples confirm the amorphous nature. The physical parameters of all the glasses were also evaluated with respect to the composition. The electron paramagnetic resonance spectra of all these glasses exhibit resonance signals that are characteristic of Cu²⁺ ions. The optical absorption spectra also confirm the Cu²⁺ ion in tetragonally elongated octahedral site. Various crystal field, spin-Hamiltonian and bonding parameters are evaluated. It is observed that the mixed alkali effect is significant.     

Optical characterization of Mn, Ni and Co ions doped zinc lead borate glasses

This paper reports on the development and optical characterization of heavy metal oxide (HMO)-based transparent glasses in the chemical composition of 15PbO-40B₂O₃-(45−x) ZnO−x TM²⁺ (=Mn²⁺ or Ni²⁺ or Co²⁺) (where x=0.2, 0.5 mol%). For these glasses both absorption and emission spectra have been measured, in order to understand their optical performances. The XRD profiles have confirmed their glassy nature and the FTIR spectral features have been analyzed. From the emission spectra, a bright green emission (538 nm) from Mn²⁺-glasses, an intense red emission (670 nm) from Ni²⁺ and from Co²⁺ (625 nm) glasses have been noticed very clearly. Based on the UV-absorption spectra of these materials, both direct and indirect bond gaps have been computed. Apart from the spectral analysis, different physical properties of these glasses have also been carried out. Due to the presence of both PbO and ZnO, these glasses are found to be good moisture-resistant optical systems. Both optical and physical properties have been found to be more encouraging towards their use as novel luminescent optical materials.     

Crystal structure and photoluminescence of (Y1−xCex)2Si3O3N4

Oxonitridosilicate phosphors with compositions of (Y_1−xCe_x)₂Si₃O₃N₄ (x=0−0.2) have been synthesized by solid state reaction method. The structures and photoluminescence properties have been investigated. Ce³⁺ ions have substituted for Y³⁺ ions in the lattice. The emission and excitation spectra of these phosphors show the characteristic photoluminescence spectra of Ce³⁺ ions. Based on the analyses of the diffuse reflection spectra and the PL spectra, a systematic energy diagram of Ce³⁺ ion in the forbidden band of sample with x=0.02 is given. The best doping Ce content in these phosphors is ∼2 mol%. The quenching temperature is ∼405 K for the 2 mol% Ce content sample. The luminescence decay properties were investigated. The primary studies indicate that these phosphors are potential candidates for application in three-phosphor-converted white LEDs.     

Dielectric and spectroscopic investigations of lithium aluminium zirconium silicate glasses mixed with TiO2

Li₂O–Al₂O₃–ZrO₂–SiO₂ glasses mixed with different concentrations of TiO₂ (ranging from 0 to 5.0?mol%) were synthesised and their dielectric properties (dielectric constant, loss tan?δ, a.c. conductivity σ) investigated over wide ranges of frequency and temperature. Studies of optical absorption, ESR, infrared (IR) and photoluminescence properties have also been undertaken. A decrease in dielectric parameters with increasing concentrations of TiO₂ has been observed and this is attributed to an increasing proportion of titanium ions occupying network-forming positions rather than going into interstitial positions. A.C. conductivity in the high-temperature region appears to be connected both to electronic transfer and ionic movements, but conduction attributed to such processes seems to be hampered by the entry of titanium ions into the network-forming positions. Analysis of the results of the IR spectral studies have indicated that there is a decreasing degree of disorder in the glass network with increasing TiO₂ content. The optical absorption and ESR spectral studies have revealed that titanium ions exist in both Ti³⁺ and Ti⁴⁺ states in the glasses. Luminescence spectra exhibited an emission band in the visible region and the luminescence efficiency increased with TiO₂ content. The excitation of substitutionally positioned octahedral Ti⁴⁺ ions is identified as being responsible for the observed luminescence emission.     

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.     

Optical characterization of Cu ion-doped zinc lead borate glasses

We have developed a new series of zinc lead borate (ZLB) glasses by varying ZnO content, to enhance UV transmission, in the chemical composition of xZnO-15PbO-(85−x)B₂O₃, where x=0, 5, 10, 15, 20, 25, 30, 35, 40 and 45 mol% ZnO. From the measurement of UV absorption spectra both the direct and indirect band gaps have been evaluated. Also different physical properties of a reference glass of 45ZnO-15PbO-40B₂O₃ have been studied. From the measurement of refractive indices at six different wavelengths, Cauchy's constants (A=1.578743209; and ) have been computed and a satisfactory correlation has been achieved between the theoretical and the experimental results. Absorption spectra of Cu²⁺(45−x)ZnO-15PbO-40B₂O₃ (where x=0.1, 0.2, 0.5 and 1.0 mol%) have shown two absorption bands at 428 nm (²B_1g→²E_g) and 777 nm (²B_1g→²B_2g). Emission spectra of (1.0 mol%) Cu²⁺:ZLB have revealed two emission transitions at 400 and 493 nm with excitations at 288 and 316 nm.     

Er3+/Yb3+共掺碲硼硅酸盐玻璃的光谱性质和热稳定性研究

制备了系列Er³⁺/Yb³⁺共掺碲硼硅酸盐玻璃样品(85-x)TeO₂-15B₂O₃-xSiO₂ (TBS x=0,5,10,15,20 mol%).测试和分析了样品的吸收光谱、荧光光谱、能级寿命、红外透射光谱及差热特性.并通过对Er³⁺离子⁴I_13/2→⁴I_15/2跃迁发射谱线的高斯拟合，设计了一个简单的四能级结构估算了Er³⁺离子⁴I_13/2和⁴I_15/2能级在碲硼硅酸盐中的Stark分裂情况.研究表明SiO₂的引入能有效地改善玻璃的热稳定性和光谱性能，玻璃析晶温度T_x与玻璃转变温度T_g之差(ΔT=T_x-T_g)可达178℃，说明碲硼硅酸盐是一种适合于光纤拉制的玻璃基质材料.比较了不同基质玻璃中Er³⁺离子的荧光半高宽和受激发射截面，结果表明TBS玻璃系统具有较好的带宽性能，是一种优良的宽带光纤放大器候选基质材料. 关键词： 碲硼硅酸盐 热稳定性 高斯拟合 -基')" href="#">OH^-基     

Prepare high efficiency Mn-doped Zn2SiO4 green phosphors in air using nano-particles

In this study, nano-scale precursors of ZnO, SiO₂, and MnO₂ powders were used to prepare mixtures with the compositions of 2ZnO+SiO₂+X mol% MnO₂ (X=MnO₂/2ZnO, abbreviated as Zn₂SiO₄-X-MnO₂), where 2≤X≤5. The mixed Zn₂SiO₄-X-MnO₂ mixtures were calcined from 900 to 1300 °C in air in order to synthesize Zn₂SiO₄:Mn²⁺ green phosphors. The X-ray diffraction patterns of Zn₂SiO₄-X-MnO₂ particles indicated that ZnO was present in the 900 °C-calcined Zn₂SiO₄-X-MnO₂ phosphors, but not in particles calcined at temperatures of 1000 °C and higher. However, the unapparent secondary phase of ZnMnO₃ was found in the 1200 and 1300 °C-calcined Zn₂SiO₄-5-MnO₂ compositions. The luminescent characteristics of Zn₂SiO₄-X-Mn²⁺ phosphors were compared with that of a commercial product (Nichia Corp., Japan). The photoluminescence (PL) intensity of 1200 °C-calcined Zn₂SiO₄-4-MnO₂ phosphors was higher and the decay times of all synthesized Zn₂SiO₄-X-MnO₂ phosphors were longer than those of the commercial product.     

Influence of valence states and co-ordination of cobalt ions on dielectric properties of PbO-Bi2O3-As2O3:CoO glass system

The glasses of the composition (40−x) PbO-15Bi₂O₃-45As₂O₃-xCoO, with 0≤x≤0.6 mol% in the steps of 0.1 were synthesized. The dielectric properties viz., dielectric constant, loss and ac conductivity over moderately larger ranges of frequency and temperature were investigated. The results were analyzed with the aid of the data on optical absorption and IR spectra. The analysis indicated that there is an increase in the insulating strength of the glasses with increase in the concentration of CoO up to 0.4 mol%.     

Structural,optical, FTIR and photoluminescence properties of Zn0.96−xCo0.04CuxO (x=0.03, 0.04 and 0.05) nanopowders

Un-hydrogenated and hydrogenated Cu, Co co-doped ZnO (Zn_0.96−xCo_0.04Cu_xO, x=0.03, 0.04 and 0.05) nanopowders have been synthesized by co-precipitation method. The synthesized samples have been characterized by powder X-ray diffraction, energy dispersive X-ray spectra, UV–Visible spectrophotometer and Fourier transform infrared spectroscopy. The calculated average crystalline size increases from 37.3 to 50.6 nm for un-hydrogenated samples from x=0.03 to 0.05 and it changes from 29.4 to 34.9 nm for hydrogenated samples. The change in lattice parameters, micro-strain, a small shift of X-ray diffraction peaks towards lower angles and reduction in energy gap reveal the substitution of Cu²⁺ ions into Zn–Co–O lattice. The hydrogenation effect reduces the particle size and induces the more uniform distribution of particles than the un-hydrogenated samples which is confirmed by SEM micrographs. Photoluminescence spectra of Zn_0.96−xCo_0.04Cu_xO system shows that red shift in near band edge ultraviolet emission from 393 to 403 nm with suppressing intensity and a blue shift in green band emission from 537 to 529 nm with enhancing intensity confirms the substitution of Cu into the Zn–Co–O lattice.