Luminescence enhancement in (Nd+Ce) doped SiO2 : Al2O3 sol–gel glasses

An enhancement in NIR luminescence from Nd³⁺-doped Ce³⁺ co-doped SiO₂+Al₂O₃ sol–gel glasses has been observed. The lasing transition (⁴F_3/2→⁴I_11/2) at 1072 nm from the dual rare-earth Nd³⁺+Ce³⁺-doped glasses has shown an emission strength of about five times that of the single rare-earth ion Nd³⁺-doped glass. From the measurement of lifetimes of the transition at 1072 nm, the transfer rate (W_tr), critical distance (R₀) and energy transfer efficiency (η) of the neodymium glasses have been calculated.     

Spectroscopic properties of Nd—doped phosphate glass with a high emission cross section

Neodymium doped phosphate glasses have been prepared by the semi-continuous melting technique. Their absorption and emission spectra have been recorded at room temperature. The Judd－Ofelt theory has been applied to evaluate the stimulated emission cross sections of ⁴F_3/2→⁴I_11/2 transition for Nd³⁺. The higher stimulated emission cross section, 4.0×10^-20cm², is obtained. The fluorescence decays of the ⁴F_3/2→⁴I_11/2 transition of Nd³⁺ are measured for the samples doped (0.7－10) wt% of Nd₂O₃ at room temperature. The concentration quenching of Nd-doped phosphate glass is mainly attributed to cross-relaxation and energy migration. The site-dependent properties of fluorescence spectra and the fluorescence lifetime of the Nd³⁺-doped phosphate glass (with 2.2wt%Nd₂O₃) are studied using laser-induced fluorescence line narrowing techniques, and the site-to-site variations of optical properties are observed at low temperature.     

Intense visible luminescence from Nd-doped yttrium oxysulfide

We report on a novel luminescent phenomenon in Y₂O₂S doped with Nd³⁺. After irradiation by a 261 nm ultraviolet (UV) light into the Y₂O₂S host lattice, the Nd³⁺-doped Y₂O₂S phosphor emits intense blue luminescence in the visible light region. Moreover, this blue luminescence can also be obtained by exciting directly into the Nd³⁺ energy absorption itself. XRD, photoluminescence, and fluorescence decay curve are used to characterize the synthesized phosphor. The spectroscopic data indicate that all the visible emission peaks are originated from the electrical transitions of Nd³⁺, and the strong luminescence of the Nd³⁺ is considered to be due to an efficient energy transfer from the Y₂O₂S host lattice to the Nd³⁺ in Y₂O₂S:Nd³⁺. The optimum concentration for the luminescence Nd³⁺ is determined to be 1 mol% of Y³⁺ in Y₂O₂S host. The critical energy transfer distance has been calculated by the concentration quenching and the possible luminescent process of this blue luminescence-emitting phosphor is also investigated.     

Influence of crystal field potential on the spectroscopic parameters of SiO2·B2O3·PbO glass doped with Nd2O3

This paper presents the optical characteristics of Nd³⁺ silicate glass (SiO₂-B₂O₃-PbO), synthesized by the fusion method. Two sets of samples were prepared: glass and corresponding glass ceramics. Optical absorption, luminescence, Raman spectroscopy and atomic force microscopy (AFM) measurements were performed in order to determine the structural properties of the systems and the radiative characteristics of Nd³⁺ ions. Near infrared luminescence exhibited typical Nd³⁺ bands. Raman and AFM measurements indicated nanocrystal growth with thermal treatment of the glass ceramics. Judd-Ofelt calculations also confirmed that heat treatment induced structural rearrangement of the samples that was dependent on Nd₂O₃ concentration. This resulted in changes in the optical and physical properties of the samples, including stimulated emission cross section and rigidity.     

Intense ultraviolet upconversion luminescence of Yb and Tb co-doped glass ceramics containing SrF2 nanocrystals

The preparation and upconversion luminescence properties of the Yb³⁺ and Tb³⁺ co-doped glass ceramics containing SrF₂ nanocrystals were investigated. The formation of SrF₂ nanocrystals was confirmed by X-ray diffraction and transmission electron microscopy. Both microstructural and spectral analysis indicated that the Yb³⁺ and Tb³⁺ ions were enriched in the precipitated SrF₂ nanocrystals, which provide much lower phonon vibration energy than the glass matrix. Due to the efficient cooperative sensitization from Yb³⁺ to Tb³⁺ and the relatively low maximum phonon energy of SrF₂ nanocrystals, the Yb³⁺ and Tb³⁺ co-doped glass ceramics exhibited intense upconversion luminescence, including ultraviolet emission at 382 nm.     

Nanocrystals formation on Ho doped strontium barium niobate glass

The study of two different methods to obtain strontium barium niobate nanocrystals immersed in a glass matrix has been carried out. Ho₂O₃-doped SrO-BaO-Nb₂O₅-B₂O₃ glasses were fabricated using the melt quenching method. Glass ceramic samples were obtained from the precursor glass by thermal treatment in a furnace and by laser irradiation. These glass ceramic samples are formed by a glassy phase and a crystalline phase of strontium barium niobate nanocrystals. This structure was confirmed by X-ray diffraction and Atomic Force Microscope images. The incorporation of Ho³⁺ ions in the strontium barium niobate nanocrystals were corroborated by optical measurements, which produced an increment in the luminescence intensity compared to the precursor glass.     

Infrared-to-visible upconversion in Er and Er/Yb activated Sb2O4 nanopowders prepared by sol-gel route

We prepared Er³⁺ doped and Er³⁺/Yb³⁺ codoped Sb₂O₄ nanocrystals by the sol-gel method. The Raman, X-ray diffraction (XRD), transmission electron microscope (TEM), and photoluminescence spectra of the samples were studied. The phonon energy of the Sb₂O₄ nanocrystals is very low (the maximum value being 461 cm⁻¹). The upconversion (UC) red emission of the Er³⁺/Yb³⁺ codoped sample is very strong at 975 nm laser diode excitation. The Sb₂O₄ nanocrystals will be a promising luminous material.     

Photoluminescent properties of Dy3+ in MgO-Ga2O3-SiO2 nano-glass-ceramic prepared by sol–gel method

The MgO-Ga₂O₃-SiO₂ (MGS) glass and glass-ceramic (GC) containing MgGa₂O₄ nanocrystals and Dy³⁺ ions were prepared by a simple sol–gel method. MgGa₂O₄ nanocrystals in MgO-Ga₂O₃-SiO₂ GC formed when the heating temperature reached 800 °C. The energy transfer from MgGa₂O₄ nanocrystals to Dy³⁺ was observed. It is important that the strong white light emission is observed corresponding to the excitation band gap of MgGa₂O₄ nanocrystals. As exciting Dy³⁺ ions, only weak yellow and blue emissions were observed.     

Improvement of Er:I11/2→Ce:F5/2 energy transfer rate in Er/Ce co-doped TeO2-ZnO-Na2O-Nb2O5 glasses

The B₂O₃ component was introduced into Er³⁺/Ce³⁺ co-doped TeO₂-ZnO-Na₂O-Nb₂O₅ glass to improve energy transfer rate of Er³⁺:⁴I_11/2→Ce³⁺:²F_5/2 phonon-assisted cross-relaxation process. With the 6 mol% substitution of B₂O₃ for TeO₂, the energy transfer rate increased from 1300 to 1831 s⁻¹ and the fluorescence intensity increased by about 13.4%. However, the more B₂O₃ substitution in the same glass system reduced the quantum efficiency of Er³⁺:⁴I_13/2→⁴I_15/2 transition due to the higher OH⁻ group concentration. The results show that an appropriate amount of B₂O₃ component can be used to improve the phonon-assisted energy transfer rate and enhance 1.53 μm fluorescence emission by increasing the phonon energy of host glass. The effect of B₂O₃ on the energy transfer process, the lifetimes of the ⁴I_11/2 and ⁴I_13/2 levels, and the upconversion emission have also been investigated.     

Luminescence studies on ZnO-P2O5 glasses doped with Gd2O3:Eu nanoparticles and Eu2O3

Zinc phosphate glasses doped with Gd₂O₃:Eu nanoparticles and Eu₂O₃ were prepared by conventional melt-quench method and characterized for their luminescence properties. Binary ZnO-P₂O₅ glass is characterized by an intrinsic defect centre emission around 324 nm. Strong energy transfer from these defect centres to Eu³⁺ ions has been observed when Eu₂O₃ is incorporated in ZnO-P₂O₅ glasses. Lack of energy transfer from these defect centres to Eu³⁺ in Gd₂O₃:Eu nanoparticles doped ZnO-P₂O₅ glass has been attributed to effective shielding of Eu³⁺ ions from the luminescence centre by Gd-O-P type of linkages, leading to an increased distance between the luminescent centre and Eu³⁺ ions. Both doped and undoped glasses have the same glass transition temperature, suggesting that the phosphate network is not significantly affected by the Gd₂O₃:Eu nanoparticles or Eu₂O₃ incorporation.     

磷酸盐玻璃中Yb3+和Nd3+之间的声子参助能量转移

本文中报道了磷酸盐玻璃中Nd³⁺,Yb³⁺的时间分辨谱和激发能量的转移。通过实验确定了在不同温度下的转移速率。证实了Nd³⁺→Yb³⁺的能量转移机构为从⁴F_3/2(Nd³⁺)到²F_5/2(Yb³⁺)并同时产生单声子发射的过程;而从Yb³⁺到Nd³⁺关键词：     

Y2O3:Eu纳米晶中能量传递相互作用的研究

通过浓度猝灭曲线确定了引起Y₂O₃纳米晶中Eu³⁺发光浓度猝灭的是交换相互作用.测量了两种颗粒尺寸下Eu³⁺的⁵D₀—⁷F₂跃迁发光衰减曲线随掺杂浓度的变化,利用交换相互作用的理论衰减曲线对实验衰减曲线进行拟合.计算Eu³⁺离子的交换相互作用能量传递的效率,分析了Y₂O_{3关键词： 能量传递 2}O₃Eu纳米晶')" href="#">Y₂O₃Eu纳米晶 发光衰减     

掺铒碲酸盐玻璃中的浓度猝灭机理研究

测试了掺铒碲酸盐玻璃在不同掺杂浓度下的荧光特性.根据Dexter能量转移理论计算了Er3+在碲酸盐玻璃中发生浓度猝灭的临界距离R₀及Er³⁺间相 互作用参 数C_Er-Er，并与其他基质玻璃中C_Er-Er数值进行了比较.最后建立 了Er³⁺基于OH^-作为猝灭中心下碲酸盐玻璃中的浓度猝灭模型. 关键词： 浓度猝灭模型 能量转移 碲酸盐玻璃 3+')" href="#">Er³⁺     

Concentration quenched luminescence and energy transfer analysis of Nd3+ ion doped Ba-Al-metaphosphate laser glasses

This paper reports the dopant ion (Nd³⁺) concentration effects on its luminescence properties in a new glass system based on barium-alumino-metaphosphates. Amongst the studied concentrations range of 0.276–13.31×10²⁰ ions/cm³, the glass with 2.879×10²⁰ ions/cm³ (1 mol%) Nd³⁺ concentration shows intense NIR emission from ⁴F_3/2 excited state, followed by a decrease in emission intensity for further increase in Nd³⁺ ion concentration. The observed luminescence quenching is ascribed to Nd³⁺ self-quenching through the donor-donor migration assisted cross-relaxation mechanism. The microscopic energy transfer parameters for donor-acceptor energy transfer, C _DA, and donor-donor energy migration, C _DD, have been obtained from the theoretical fittings to experimental decay curves and the spectral overlap model respectively. The C _DD parameters (×10^?39 cm⁶/sec) are found to be about three orders greater than that of C _DA (×10^?42 cm⁶/sec) for Nd³⁺ self-quenching in this host, demonstrating that the excitation energy migration among donors is due to the hopping mechanism. The energy transfer micoparameters obtained in the present study are comparable to the values reported for commercially available laser glasses LHG-8 and Q-98.     

Spectroscopic properties of Nd3+-doped tungsten–tellurite glasses

In this work, we investigate the spectroscopy properties of neodymium doped tungsten–tellurite glasses prepared in ambient and O₂-rich atmospheres. A conversion of TeO₄ to TeO₃ units was caused by the addition of Nd³⁺ into the glass, which was confirmed by absorption spectra and by Judd–Ofelt parameter behavior. The relaxation of the ⁴F_3/2 level is dominated by radiative decay and cross-relaxation between Nd³⁺ and Nd³⁺ ions. The energy transfer from Nd³⁺ to the hydroxyl group is negligible when compared to the cross-relaxation. The luminescence quantum efficiency values of the ⁴F_3/2 level decreases as the Nd³⁺ concentration increases, independently if determined by the Judd–Ofelt method or by the thermal lens technique. The observed reduction in the IR absorption associated to OH groups was not effective to improve the luminescence quantum efficiency.     

Energy transfer from the host to Er<Superscript>3+</Superscript> dopants in semiconductor SnO<Subscript>2</Subscript> nanocrystals segregated in sol–gel silica glasses

Undoped and Er³⁺-doped glass–ceramics of composition (100−x)SiO₂–xSnO₂, with x = 5 or 10 and with 0.4 or 0.8 mol% of Er³⁺ ions, were synthesised by thermal treatment of precursor sol–gel glasses. Structural studies were developed by X-Ray Diffraction. Wide band gap SnO₂ semiconductor quantum-dots embedded in the insulator SiO₂ glass are obtained. The mean radius of the SnO₂ nanocrystals, ranging from 2 to 3.2 nm, is comparable to the exciton Bohr radius. The luminescence properties have been analysed as a function of sample composition and thermal treatment. The results show that Er³⁺ ions are partially partitioned into the nanocrystalline phase. An efficient UV excitation of the Er³⁺ ions by energy transfer from the SnO₂ nanocrystal host is observed. The Er³⁺ ions located in the SnO₂ nanocrystals are selectively excited by this energy transfer mechanism. On the other hand, emission from the Er³⁺ ions remaining in the silica glassy phase is obtained by direct excitation of these ions.     

Time Resolved Fluorescence and Energy Transfer Analysis of Nd<Superscript>3+</Superscript>–Yb<Superscript>3+</Superscript>–Er<Superscript>3+</Superscript> Triply-Doped Ba–Al-Metaphosphate Glasses for an Eye Safe Emission (1.54 μm)

This paper reports on the preparation and systematic analysis of energy transfer mechanisms in Nd³⁺–Yb³⁺–Er³⁺ co-doped new series of barium-alumino-metaphosphate glasses. The time resolved fluorescence of Nd³⁺ in triply doped Ba–Al-metaphosphate glasses have revealed that, Yb³⁺ ions could function as quite efficient bridge for an energy transfer between Nd³⁺ and Er³⁺ ions. As a result, a fourfold emission enhancement at 1.54 μm of Er³⁺ ions has been achieved through an excitation of ⁴F_5/2 level of Nd³⁺ at 806 nm for the glass having 3 mol% Yb³⁺ with an energy transfer efficiency reaching up to 94%. Decay of donor (Nd³⁺) ion fluorescence has been analyzed based on theoretical models such as direct energy transfer model (Inokuti–Hirayama) and migration assisted energy transfer models (Burshtein’s hopping and Yokota–Tanimoto’s diffusion). The corresponding energy transfer parameters have been evaluated and discussed. Primarily, electrostatic dipole–dipole (s ~ 6) interactions are found to be responsible for the occurrence of energy transfer process in theses glasses.     

Nd photoluminescence study of Nd-doped Si-rich silica films obtained by reactive magnetron sputtering

Nd³⁺-doped silicon-rich silicon oxide (SRSO) thin films have been fabricated by reactive magnetron sputtering of a pure silica target topped with Nd₂O₃ chips. The concentration of Nd ions in the deposited layers is controlled by the number of Nd₂O₃ chips, whereas the incorporation of silicon excess is monitored by the hydrogen partial pressure, P_H2, introduced in the Ar plasma, owing to the ability of hydrogen to reduce the oxygen released by the sputtering of the silica target. Photoluminescence (PL) experiments were made at room temperature using a nonresonant excitation line from an Ar laser. The influences of Nd³⁺ content and P_H2 have been studied to optimize the Nd³⁺ emission. PL spectra reveal a two order of magnitude enhancement of the Nd³⁺ emission around both 0.9 and 1.1 μm, when Si nanoclusters (Si-nc) are formed in the same Nd³⁺-doped matrix. The dependence of the Nd³⁺ PL with P_H2 and Nd concentration is indicative of the occurrence of an efficient energy transfer from the Si-nc to the rare earth ions. The radiative lifetime is also deduced and commented in the light of Nd³⁺-Si-nc coupling.     

Luminescence of aluminoborosilicate glasses doped with Gd3+ ions

The two-photon absorption that leads to the ultraviolet upconversion luminescence in the SiO₂-Al₂O₃-B₂O₃-Na₂O₃-Zr₂O: Cd³⁺ glass has been investigated. The inference has been made that no photon cascade emission takes place under excitation by monochromatic light corresponding to the maximum of the absorption band of the Cd³⁺ ion (204 nm). The mechanisms of concentration quenching and energy transfer between Cd³⁺ ions and optically active defects of the aluminoborosilicate glass have been discussed.     

Optical properties of (ZnO)0.5(P2O5)0.5 glasses doped with Gd2O3:Eu nanoparticles and Eu2O3

Binary (ZnO)_0.5(P₂O₅)_0.5 glasses doped with Eu₂O₃ and nanoparticles of Gd₂O₃:Eu were prepared by conventional melt-quench method and their luminescence properties were compared. Undoped (ZnO)_0.5(P₂O₅)_0.5 glass is characterized by a luminescent defect centre (similar to L-centre present in Na₂O-SiO₂ glasses) with emission around 324 nm and having an excited state lifetime of 18 ns. Such defect centres can transfer the energy to Eu³⁺ ions leading to improved Eu³⁺ luminescence from such glasses. Based on the decay curves corresponding to the ⁵D₀ level of Eu³⁺ ions in both Gd₂O₃:Eu nanoparticles incorporated as well as Eu₂O₃ incorporated glasses, a significant clustering of Eu³⁺ ions taking place with the latter sample is confirmed. From the lifetime studies of the excited state of L-centre emission from (ZnO)_0.5(P₂O₅)_0.5 glass doped with Gd₂O₃:Eu nanoparticles, it is established that there exists weak energy transfer from L-centres to Eu³⁺ ions. Poor energy transfer from the defect centres to Eu³⁺ ions in Gd₂O₃:Eu nanoparticles doped (ZnO)_0.5(P₂O₅)_0.5 glass has been attributed to effective shielding of Eu³⁺ ions from the luminescence centre by Gd-O-P type of linkages, leading to an increased distance between luminescent centre and Eu³⁺ ions.