Spectroscopic and photoluminescence characteristics of Dy ions in lead containing sodium fluoroborate glasses for laser materials

Lead containing calcium zinc sodium fluoroborate (LCZSFB) glasses doped with different concentrations of trivalent dysprosium ions were prepared and investigated by the XRD, FTIR, optical absorption, photoluminescence and decay curve analysis. The experimentally determined oscillator strengths have been determined by measuring the areas under the absorption peaks and the Judd–Ofelt (J–O) intensity parameters were calculated using the least squares fit method. From the evaluated J–O parameters the radiative transition probability rates, radiative lifetimes and branching ratios were calculated for ⁴F_9/2 excited level. Room temperature photoluminescence spectra for different concentrations of Dy³⁺-doped LCZSFB glasses were obtained by exciting the glass samples at 386 nm. The intensity of Dy³⁺ emission spectra increases with increasing concentration of 0.1, 0.25, 0.5 and 1.0 mol% and beyond 1.0 mol% the concentration quenching is observed. The measuring branching ratios are reasonably high for transitions ⁴F_9/2→⁶H_15/2 and ⁶H_13/2, suggesting that the emission at 484 and 576 nm, respectively, can give rise to lasing action in the visible region. From the visible emission spectra, yellow–blue (Y/B) intensity ratios and chromaticity color coordinates were also estimated. The lifetimes of ⁴F_9/2 metastable state for the samples with different concentrations were also measured and discussed.     

Thermal and optical properties of Er-doped oxyfluorotellurite glasses

Er³⁺-doped oxyfluorotellurite glasses with four different concentrations of Er³⁺ ions have been prepared and investigated their thermal, optical absorption, excitation and luminescence properties. From the DSC spectra, glass transition and onset of crystallization temperatures have been found. Judd-Ofelt intensity parameters have been derived from the absorption spectrum and are in turn used to calculate radiative properties for the important luminescent levels of Er³⁺ ions. The calculated radiative properties are comparable to experimental values. The glasses show intense green and weak red emission under normal excitation with 451 nm. The decrease in emission intensities and lifetimes of the ⁴S_3/2 level with concentration of Er³⁺ ions has been explained as due to energy transfer processes between Er³⁺ ions. The stimulated emission cross-sections and quantum efficiencies of the green and infrared emissions have been determined. The results indicate that the glasses may be suitable for use as a laser medium in making solid-state green laser by normal pumping route and as laser medium and optical amplifier in the 1.5 μm region.     

Spectroscopic properties of Sm3+ ions in lead fluorophosphate glasses

The Sm³⁺-doped lead fluorophosphate glasses of composition 44P₂O₅–17K₂O–9Al₂O₃–(24?x)PbF₂–6Na₂O–xSm₂O₃, where x=0.01, 0.05, 0.1, 0.5, 1.0 and 2.0 mol%, have been prepared by conventional melt quenching technique and are characterized through differential thermal analysis, Raman, absorption and emission spectra and decay rate measurements. Free-ion Hamiltonian model for energy level analysis and Judd–Ofelt theory for spectral intensities have been used to analyze the spectroscopic properties of Sm³⁺ ions in lead fluorophosphate glasses. The decay rates for the ⁴G_5/2 level of Sm³⁺ ions have been measured and are found to be single exponential at lower concentration (≤0.1 mol% Sm₂O₃) and turn into non-exponential at higher concentrations (≥0.5 mol% Sm₂O₃) due to energy transfer through cross-relaxation. The experimental lifetimes for ⁴G_5/2 level of Sm³⁺ ions are found to decrease from 2.54 to 0.92 ms when the concentration increased from 0.01 to 2.0 mol% Sm₂O₃ due to energy transfer. In order to know the nature of the energy transfer mechanism, the non-exponential decay rates are well fitted to Inokuti–Hirayama model for S=6, which indicates that the energy transfer process is of dipole–dipole type.     

The effect of Er3+-ion concentration on the Er3+ : 4I13/2 → 4I15/2 transition in tellurite glasses

The effect of Er³⁺ concentration on the Er³⁺?:?⁴I_13/2?→?⁴I_15/2 emission in tellurite glasses has been investigated. The full width at half-maximum increased with the increasing concentration of Er₂O₃ in tellurite glasses. The effect of local structure of Er³⁺ ions and related spectroscopic changes are taken into account to explain the line broadening. Inhomogeneous broadening due to the distribution of crystal field around the Er³⁺ ion has little effect on the absorption spectra. Highly efficient energy trapping between the ions was identified from the time-resolved analysis of the fluorescence decay and is found to be responsible for the extended lifetime at intermediate concentrations of Er³⁺ ions in tellurite glasses. The effect of temperature on spectral line shape has been determined for analysing the contribution of Boltzmann population on line broadening. The increased population of the overlying Stark sublevels at the ⁴I_13/2 energy level via direct pumping and/or interaction between Er³⁺ ions were also found to be significant for enhancement in spectral line shape at higher concentrations of Er³⁺ ions in tellurite glasses. It was observed that at higher concentrations of Er³⁺ ions in glass also enhance the local symmetry of ions, which is apparent from the absorption band of the Er³⁺?:?⁴I_15/2?→?²H_11/2 hypersensitive transition.     

Luminescence properties of Tb doped and Tm/Tb/Sm co-doped glasses for LED applications

Tb³⁺ ions doped and Tm/Tb/Sm co-doped glasses for light-emitting-diodes (LED) applications have been synthesized by melt quenching method. Their photoluminescence properties were studied by emission and excitation spectra. The ⁵D₃ and ⁵D₄ emission of Tb³⁺ can be varied by adjusting Tb³⁺ concentrations and the compositions of glass matrix. Blue, green and reddish orange emission bands were observed in the emission spectra of Tm/Tb/Sm co-doped glasses. The combination of these emission bands allows the realization of white light when the glasses are excited by near ultraviolet light. In addition, the relative intensity ratios of respective emission lines are dependent on the composition of glasses and the excitation wavelength.     

Rare-Earth Doped Sol-Gel Silicate Glasses for Scintillator Applications

Radio-, photo- and thermally stimulated—luminescence (RL, PL, TSL) measurements have been performed on SiO₂ sol-gel glasses doped by 0.1 mol% Ce and 3 mol% Gd, and on (0.1 mol% Ce, 3 mol% Gd) co-doped samples. Ce^3? 5d-4f emission peaking at about 2.7 eV has been observed in the RL of SiO₂: 0.1 mol% Ce, while the typical ⁶P-⁸S emission of Gd^3? centred at 3.97 eV has been detected in SiO₂: 3 mol% Gd. The co-doped sample displays both 5d-4f Ce^3? and ⁶P-⁸S Gd^3? emissions with reduced intensities with respect to those observed in the singly doped glasses. Moreover, in co-doped glasses the PL time decay patterns of both rare earth ions show a non exponential dependence and are significantly shortened. To explain such an effect non radiative de-excitation of both RE ions excited states involving energy transfers to defect levels is suggested. Bidirectional Gd^3? ? Ce^3? energy transfers could also occur. Complementary TSL measurements put in evidence the existence of broad glow peaks at about 100 K and 220 K. The TSL spectra feature the RE ions emissions.     

Photoluminescence and decay behavior of Tb3+ ions in sodium fluoro-borate glasses for display devices

We report the optical absorption, photoluminescence and fluorescence decay properties of Tb³⁺-doped sodium fluoro-borate (SFB) glasses. Different concentrations of Tb³⁺-doped SFB glasses were prepared by conventional melt quenching technique using a chemical composition (in mol%) 25Na₂O–5LaF₃–10CaF₂–10AlF₃–(50?x) B₂O₃?x TbF₃ (0.01≤x≥4). The Judd-Ofelt model has been adopted to determine the radiative parameters of the ⁵D₄→⁷F_6–3 emission transitions. The effect of Tb³⁺ ion concentration on the emission from the ⁵D_3,4 excited levels is discussed in detail. The analysis of optimization of Tb³⁺ ion concentration for efficient green color display devises is reported. The resonance energy transfer mechanism responsible for non-radiative decay rates is clearly explored.     

Rare-earth doped YF3 nanocrystals embedded in sol–gel silica glass matrix for white light generation

YF₃ nanocrystals triply-doped with Yb³⁺, Ho³⁺ and Tm³⁺ ions embedded in amorphous silica matrix have been successfully obtained by heat treatment of precursor sol–gel glasses for the first time to our knowledge and confirmed by X-ray diffraction and luminescence measurements. Simultaneous UV and visible efficient up-conversion emissions, with well-resolved Stark structure, under 980 nm infrared pump are observed, indicating the effective partition of rare-earth ions into a crystalline-like environment of the YF₃ nanocrystals. Corresponding energy transfer mechanisms have been analyzed and overall colour emission has been quantified in terms of standard chromaticity diagram. By an adequate doping level and heat treatment temperature of precursor sol–gel glasses, a bright white colour has been accomplished, close to the standard equal energy white light illumination point, with potential applications in photo-electronic devices and information processing.     

Pr3+/Ho3+共掺Ge-Ga-Se玻璃的2.9 μm荧光特性的研究

采用熔融冷却法制备了系列Ho³⁺/Pr³⁺共掺的Ge₂₅Ga₁₀Se₆₅玻璃样品,测试了样品的吸收光谱以及908 nm激光抽运下的中红外荧光光谱和Ho³⁺离子⁵I₇能级寿命.计算了Ho³⁺:⁵I₇→⁵I₈发射截面和Pr³⁺:³H₄→³F₂吸收截面,讨论了Ho³⁺,Pr³⁺离子之间的能量转移效率及Pr³⁺离子浓度的影响.通过拟合Ho³⁺离子2.0 μm荧光衰减曲线判断能量转移机理.结果表明,Ho³⁺掺杂Ge₂₅Ga₁₀Se₆₅玻璃中引入Pr³⁺离子可以有效提高Ho³⁺离子的2.9 μm荧光强度. 关键词： 中红外发光 硫系玻璃 3+/Pr³⁺共掺')" href="#">Ho³⁺/Pr³⁺共掺     

Er3+离子掺杂钡镓锗玻璃上转换发光机理研究

研究了Er³⁺离子掺杂钡镓锗玻璃的吸收光谱、拉曼光谱和上转换光谱.分析了Er³⁺离子在钡镓锗玻璃中的上转换发光机理.结果表明：玻璃的最大声子能量为828cm^-1，紫外截止波长为275nm.采用800nm和980nmLD激发玻璃样品，在室温下观察到强烈的上转换绿光和红光发射.随着Er³⁺离子浓度的增加，绿光发光强度先增加后减小，而红光发光强度呈单调递增趋势.能量分析表明：800nmLD激发产生的绿光主要源于Er³⁺离子4I_13/2能级的激发态吸收过程；红光发射主要源于Er³⁺离子4I_13/2能级与4I_11/2能级之间的能量转移过程.980nmLD激发产生的绿光主要源于Er³⁺离子4I_11/2能级之间的能量转移过程；而红光发射主要源于Er³⁺离子4I_13/2能级与4I_11/2能级之间的能量转移过程和4I_13/2能级的激发态吸收过程.通过量子效率分析，发现采用800nmLD激发Er³⁺离子掺杂浓度为1mol% 的样品时，上转换绿光发光效率最高. 关键词： 上转换发光机理 3+离子掺杂')" href="#">Er³⁺离子掺杂 钡镓锗玻璃     

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 properties and site distribution of Cr ions in alkali-disilicate glasses

The optical properties of the low-field sites of Cr³⁺-doped alkali (Li, Na, K) disilicate glasses have been investigated using the single configurational coordinate model. The assumption of a Gaussian site distribution for the Cr³⁺ ions taking as parameter the zero-phonon energy has been considered. For alkali disilicate glasses the inhomogeneous contribution to the broadening of the bands, associated to the site distribution, is lower than the homogeneous one. The electron-lattice coupling S and the mean phonon energy ?ω₀ have been obtained with results around 4 and 500 cm⁻¹, respectively, similar to those obtained by other authors in oxide glasses. The site-resolved study of the emission and excitation spectra and the luminescence decay curves have been carried out as a function of temperature. On the one hand, there is evidence of a non-radiative de-excitation process that becomes important over 140 K. On the other hand, and related to the site dependence of the radiative and non-radiative probabilities, different results involving low values for the quantum efficiencies and blue shifts of the emission bands as temperature increases have been explained. Besides, the non-exponential luminescence decay curves have been fitted to an expression proposed by the authors, which takes into account non-coupled distributions for the radiative and non-radiative de-excitation probabilities for the range of temperature covering from 13 to 300 K. From the fits, the temperature dependence of the non-radiative de-excitation probability is obtained for each disilicate glass, the results are in good agreement with the expression obtained assuming the harmonic approximation in the single configurational coordinate model.     

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.     

Concentration-dependent luminescence of Tb ions in high calcium aluminosilicate glasses

This study deals with the results on the concentration-dependent fluorescence properties of Tb³⁺-doped calcium aluminosilicate (CAS) glasses of composition (100−x)(58SiO₂–23CaO–5Al₂O₃–4MgO–10NaF in mol%)-x Tb₂O₃ (x=0, 0.25, 0.5, 1, 2, 4, 8, 16, 24, 32, 40 in wt%). The FTIR reflectance spectra suggested the role of dopant ions as network modifiers in the glass network. The fluorescence spectra of low Tb³⁺-doped glasses have revealed prominent blue and green emissions from ⁵D₃ and ⁵D₄ excited levels to ⁷F_j ground state multiplet, respectively. The glass with 2 wt% of Tb₂O₃ has exhibited maximum intensity of blue emission from ⁵D₃ level, while green emission from ⁵D₄ level has increased linearly up to 24 wt% and showed reduction in the rate of increase for higher Tb₂O₃ concentrations. The concentration quenching of blue emission (⁵D₃→⁷F_j) is attributed mainly to the resonant energy transfer (RET) assisted cross-relaxation (CR) among the excited and nearest neighbour unexcited Tb³⁺ ions in the glass matrix. The decline in rate of increase of green emission (⁵D₄→⁷F_j) at higher concentrations has been explained due to a possible occurrence of cooperative energy transfers leading to 4f⁸→4f⁷5d transition interactions. The blue and green emission decay kinetics have been recorded to compute the excited level (⁵D₃ and ⁵D₄) lifetimes, which confirmed the Tb³⁺ concentration quenching of the blue emission in these glasses.     

Rare earth ion distribution in sol–gel silicate glasses

Sol–gel glasses are porous networks that have been densified through chemical processing and heat treatment. Due to their relative insolubility in silica, rare earth (RE) ions in silicate glasses enter as network modifiers and compete for non-bridging oxygens in order to complete their coordination. Energy transfer between Tb³⁺ ions is used here to study the distribution of RE ions in these porous glasses. The non-exponential decay of the ⁵D₃ fluorescence is due to cross relaxation. Using a model for energy transfer in fractional dimensions and fitting the decay profile to a stretched exponential, the number of nearby Tb³⁺ ions and the dimensionality of the Tb³⁺ ions in the pores could be determined. Analysis indicates that the observed fluorescence originates from relatively isolated ions. Samples annealed below 950 °C exhibit a dimensionality of ～1.2.     

Visible upconversion emissions in Pr3+-doped TeO2–ZnO glass

The Pr³⁺-doped tellurite zinc oxide (TZO) glasses by conventional melt and quenching technique have been prepared. The absorption spectra of samples doped with different concentrations of triply ionized praseodymium ions have been analyzed. Several upconversion emission bands of the Pr³⁺ ions doped in tellurite zinc oxide glasses under 980?nm excitation have been observed. The possible excitation mechanisms responsible for upconversion emissions spanning from blue to near infrared region have been discussed in detail.     

Investigation on luminescence and energy transfer in Tb-doped lead telluroborate glasses

This work reports on the visible luminescence properties and energy transfer processes responsible for non-exponential nature of the decay curves and also quenching of luminescence intensity of the ⁵D₃→⁷F_J transitions of Tb³⁺ ions in lead telluroborate (PTB) glasses containing different Tb³⁺ concentrations. The XRD and FT-IR spectra were measured to study the glassy nature and composition of the prepared glasses. The radiative properties are determined using the Judd-Ofelt theory to judge the suitability of studied glasses as practical photonic material. These parameters suggest that the PTBTb20 glass has the potential to produce intense green emission (544 nm) through the ⁵D₄→⁷F₅ transition.     

An investigation on visible luminescence of Ho activated LBTAF glasses

Different concentrations of Ho³⁺-doped lead borate titanate aluminum fluoride (LBTAFHo) glasses with chemical composition of PbO-H₃BO₃-TiO₂-AlF₃-Ho₂O₃ were prepared by the melt quenching method. The spectral properties were investigated using the absorption, emission and decay measurements. The experimental oscillator strengths were calculated from the area under the absorption bands. Applying Judd-Ofelt theory, the intensity parameters (Ω_{λ=2, 4, 6}) were calculated, by the least square fit approach from which the radiative transition rates, luminescence branching ratios and radiative decay times were determined. The photoluminescence spectra revealed the quenching of luminescence intensity beyond 1.0 mol% of Ho³⁺ ion concentration. To investigate the luminescence potentiality of ⁵F₄→⁵I₈ emission level, the effective bandwidth and the stimulated emission cross-section were determined. The quenching in experimental decay time is attributed to the resonance energy transfer among the excited Ho³⁺ ions.     

Photoluminescence and energy transfer of Tm doped LiIn (WO4)2 blue phosphors

Room temperature steady and time resolved emission spectra of LiIn_1−xTm_x(WO4)2 (where thulium concentration is 0, 0.5, 1, 5 and 10 at%) blue phosphors, under UV excitation energy have been investigated. The concentration quenching effect on the blue emission, due to the (WO₄)⁻² groups and ¹G₄→³H₆ emission transition of Tm³⁺ were studied. Two energy transfer mechanisms are shown. The first takes place between excited (WO₄)⁻² groups and the ¹G₄ energy level of Tm³⁺, and is mainly analyzed by phonon-assisted energy transfer. The second mechanism is due to an energy transfer from the excited Tm³⁺ ions to the surrounding ground state Tm³⁺ ions. The non-exponential decay curves of the ¹G₄ level observed for higher concentrations are analyzed by the Inokuti–Hirayama model. We think that the quenching effect between Tm³⁺ ions is mainly linked to the dipole–dipole interactions.