Non-exponential Nature Research Articles

A study of optical properties of Tm3+ ions in Y2Te4O11 microcrystalline powder

The Y2-xTe4O11 (x = 0.1, 0.5, 1.0, 2.0 and 5.0 at%) microcrystalline powders were successfully synthesized by a conventional solid state reaction method. Optical absorption (300 K) and fluorescence spectra (300 K) as well as fluorescence decay curves (300 K) of the emitting levels of Tm3+ ion in Y2Te4O11 powders are presented and analyzed in details. The Judd-Ofelt theory was applied to analyze experimental data for the quantitative determination of phenomenological Ωλ (λ = 2, 4, 6) parameters, radiative transition probabilities (A), branching ratios (β) of luminescence and radiative lifetimes (τrad) of the 1D2, 1G4, 3H4 and 3F4 levels. The observed non-exponential decays nature and concentration quenching of the 1G4 and 3H4 states have been attributed to cross-relaxation processes and this phenomena has been analyzed by Inokuti-Hirayama model. The stimulated emission cross-section for the 3F4 → 3H6 transition equals to 1.12 × 10−20 cm2 at 1809 nm was calculated using the Füchtbauer-Ladenburg method and compared with the corresponding values of other Tm3+-doped laser hosts. From obtained results, follow that the Tm3+:Y2Te4O11 is a potential candidate for a solid-state laser host operating at 1.8 µm.

Investigation of Green and 1.53 μm emission characteristics of Er3+ doped bismuth phosphate glasses for laser applications

Erbium (Er3+) ion doped bismuth phosphate (BiP) glasses were fabricated by melt quenching technique. In the current project, studied the influence of bismuth content and Er3+ ion doping concentration on photoluminescence (PL) performance and therefore find out the most qualified combination of bismuth and Er3+ for developing compact optical fibre lasers and amplifiers operating at 1.53 μm. Optical absorption measurements are carried out and analysed through Judd-Ofelt (JO) and Mc-Cumber theories from which JO parameters, absorption and stimulated emission cross-sections are determined. The studied glasses show intense and broad visible emission at 545 nm (green) for 4S3/2 → 4I15/2 transition with the excitation 379 nm might be useful for green laser applications. The luminescence behaviour of 4I13/2 → 4I15/2 transition in the wavelength region 1400–1700 nm and its suitability for optical amplifier applications and also for NIR laser have been discussed with parameters such as stimulated emission cross-section (σe), gain bandwidth (ΔG) and optical gain (G). The decay curves for both 4S3/2 (visible) and 4I13/2 (NIR) levels are discussed and they are exhibiting non-exponential nature for all the studied BiP glasses. Among all the BiP glasses, Er-1.0 glass exhibited higher σe, ΔG and G values suggesting the suitability for optical amplifier and NIR laser applications.

Photoluminescence, γ-irradiation and X-ray induced luminescence studies of Sm3+-doped oxyfluorosilicate glasses and glass-ceramics

Sm3+-doped oxyfluorosilicate glasses were fabricated through traditional melt quenching technique. After the heat treatment of the prepared glass, transparent SrF2 nanocrystalline glass-ceramics (GC) were obtained. The amorphous nature of the prepared glasses and crystalline phase (SrF2) of the GC were confirmed by XRD analysis. Abbe number was calculated for all the prepared glasses by measuring refractive index at different wavelengths. In the framework of Judd-Ofelt (JO) theory, the JO intensity parameters were obtained from the absorption spectra of 1.0mol% Sm2O3-doped glass. The photoluminescence spectrum was recorded with 401nm excitation. From the analysis of optical spectra and JO parameters, the radiative properties like radiative transition probabilities, branching ratios and radiative lifetimes for the fluorescent levels of Sm3+ ions were determined. The effect of γ-irradiation on luminescence properties and X-ray induced luminescence properties were also studied. The emission intensity was increased for GC where as it decreases with increase of γ-irradiation dosages. There are no noticeable changes in the position as well as intensity in photoluminescence and X-ray induced luminescence spectra for GC sample but after the γ-irradiation, the emission intensity was decreased moderately. The luminescence decay profiles for 4G5/2 level were recorded and it is changed from exponential to non-exponential nature for higher Sm3+ ion concentrations. The decay profiles which exhibit non-exponential nature are well fitted to the Inokuti-Hirayama model and determined the energy transfer parameters. By using the integrating sphere, the quantum yield values were obtained for all the prepared glasses. The detailed study of the present glasses reveals that these glasses could be useful for radiation shielding and scintillation applications.

Optical spectroscopy and emission properties of Ho3 +-doped gadolinium calcium silicoborate glasses for visible luminescent device applications

The Ho3+-doped gadolinium calcium silicoborate glasses with the composition of 25Gd2O3+10CaO+10SiO2+(55−x)B2O3+xHo2O3, where x=0.0, 0.5, 1.0, 1.5, 2.0 and 2.5mol%, were synthesized by well-known melt quenching method. These glasses have been characterized through physical, structural, optical, visible emission and decay curve analysis. From the absorption spectrum, Judd-Ofelt intensity parameters for 1.0mol% Ho2O3 doped glass have been carried out and were used to examine radiative properties for the important visible emitting levels of Ho3+ ions. The present Ho3+:glasses show strong green emission at 545nm and red emission at 655nm under excitation at 452nm. The radiative decay time and stimulated emission cross-section for the (5S2,5F4)→5I8 transition are found to be 280 μs and 0.63×10−20cm2, respectively. Decay curves for all the concentration of Ho3+ ions exhibit non-exponential nature for (5S2,5F4)→5I8 transition. The decrease in decay times is due to the resonant energy transfer among the excited Ho3+ ions. Hence, these results confirm that the present silicoborate glass system could be considered as a promising candidate for visible green laser applications.

Physical, vibrational, optical and luminescence investigations of Dy3+-doped yttrium calcium silicoborate glasses for cool white LED applications

The Dy3+-doped yttrium calcium silicoborate glasses of composition of 25Y2O3 + 10CaO + 10SiO2 + (55-x)B2O3 + x Dy2O3, where x = 0.05, 0.1, 0.5, 1.0, 1.5, 2.0 and 2.5 mol%, have been synthesized and are characterized through optical, photoluminescence and X-ray induced luminescence properties. The Judd-Ofelt model has been adopted to evaluate the radiative properties of the 4F9/2 → 6HJ (J = 15/2, 13/2 and 11/2) emission transitions. The concentration quenching effect of Dy3+ ion concentration on the emissions from the 4F9/2 excited level is discussed in details. The luminescence decay curves of the 4F9/2 level transform from exponential to non-exponential nature for higher Dy3+ ion concentration. The yellow to blue (Y/B) intensity ratio, CIE Chromaticity coordinates and correlated color temperatures (CCT) were calculated from the emission spectra and were found that they fall in yellowish white light region. Thus, these results showed that the present YCaSBDy glasses could be aptly suitable for cool white light emitting diodes as well as glass scintillation applications.

Structure, morphology and optical characterization of Dy3+-doped BaYF5 nanocrystals for warm white light emitting devices

The barium yttrium fluoride BaYF5 nanocrystalline powders doped with different concentrations of Dy3+ ions have been synthesized via a hydrothermal method and studied their structural, morphological, thermal, vibrational, and optical properties. These nanopowders have been crystallized in a single phase of the tetragonal structure with the average size of around 30 nm having spherical shape in morphology. Upon excitations at 350 and 387 nm, Dy3+ -doped BaYF5 nanocrystals exhibit strong blue and yellow emissions ascribed to the 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions, respectively. Decay curves of the 4F9/2 level of Dy3+ ion in BaYF5 nanocrystals exhibit non-exponential nature due to the dipole-dipole interaction between Dy3+ ions, confirmed by Inokuti-Hirayama model. The quantum yield for these nanocrystals have been found to be increased from 4.64% to 11.61% as the concentration of Dy3+ ions increases from 1.0 mol% to 2.0 mol% and then decreased to 10.68% as the dopant concentration increased to 5.0 mol%. Moreover, color coordinates and correlated color temperatures have been evaluated as a function of concentration and excitation wavelength and found to be in the warm white light region for all Dy3+ concentrations.

Single phase GdPO4: Dy3+ microspheres blue, yellow and white light emitting phosphor

Luminescent microspheres, Gd(1−x)DyxPO4 have been synthesized using simple combustion method for the first time. SEM images show that the obtained powders are formed by dispersed microscaled spheres with diameter ranging from 0.5 to 1 μm. The X-ray diffraction, FTIR and Raman spectroscopy studies reveal that the microparticles annealed at 800 °C crystallized in a monoclinic phase with space group P21/n. Under host Gd3+ sensitization, Gd(1−x)DyxPO4 emission spectra of Dy3+ show a broad blue band attributed to transitions 4I15/2 + 4I13/2 + 4I11/2 + 4F9/2 → 6H15/2, a sharp yellow band due to 4F9/2 → 6H13/2 transition, and the little red band of 4F9/2 → 6H11/2 transition. Blue and white emissions have been obtained at low and high Dy3+ concentration, respectively due the energy transfer from Gd3+ to Dy3+. Under direct 4f–4f excitation of Dy3+ in GdDPO4, three bands attributed to 4F9/2 → 6H15/2, 6H13/2, 6H11/2 transitions have been observed resulting in a yellow light emission. The emission bands intensity are discussed as function of GdPO4 structure. They are in well agreement with crystal structure of the host lattice GdPO4 in contrast to reported works. The decay rates for the 4F9/2 level are found to be deviated from exponential to non-exponential nature with increase of Dy3+ concentration. A promising white-light emission for white LED operating under UV excitation is investigated from single-phased phosphor. The obtained results suggest a potential application of GdPO4:Dy3+ microspheres as alternatives to replace bulk materials for many application fields, including light display systems and optoelectronic devices.

Fluorescence properties and white light generation from Dy3+-doped niobium phosphate glasses

Niobium phosphate glasses (P2O5+Nb2O5+K2O + Al2O3+Dy2O3) doped with different concentrations of Dy3+ ions have been synthesized by melt quenching technique and characterized through structural and optical measurements to evaluate the fluorescence properties and find their suitability for white light emitting diodes (LEDs). Phonon energy and vibrational groups of the host matrix have been analyzed from Raman spectra. Judd-Ofelt analysis has been applied for 1.0 mol% Dy2O3-doped glass and inturn radiative properties have been evaluated for excited states of the Dy3+ ion. The higher value of stimulated emission cross-section (σe = 6.4 × 10−21 cm2) for the 4F9/2 → 6H13/2 level confirms its potentiality to be used as yellow laser. The decay curves exhibit non-exponential nature at higher concentrations (≥1 mol %) of Dy3+ ion. From the decay curve analysis, the quantum efficiency for the 4F9/2 level of 1.0 mol % Dy3+-doped glass is found to be 92%. The yellow to blue intensity ratios and chromaticity color co-ordinates are found to vary with Dy3+ ion concentrations/excitation wavelengths and are within the white light region.

A novel model on time-resolved photoluminescence measurements of polar InGaN/GaN multi-quantum-well structures

Based on carrier rate equation, a new model is proposed to explain the non-exponential nature of time-resolved photoluminescence (TRPL) decay curves in the polar InGaN/GaN multi-quantum-well structures. From the study of TRPL curves at different temperatures, it is found that both radiative and non-radiative recombination coefficients vary from low temperature to room temperature. The variation of the coefficients is compatible with the carrier density of states distribution as well as the carrier localization process. These results suggest that there is a novel method to calculate the internal quantum efficiency, which is a complement to the traditional one based on temperature dependent photoluminescence measurement.

Simulation of Deep-Level Trap Distributions in AlGaN/GaN HEMTs and Its Influence on Transient Analysis of Drain Current

AlGaN/GaN high electron mobility transistors for high efficiency power switching applications are susceptible to charge trapping by deep-levels in the GaN buffer resulting in current collapse during gate and drain voltage swings. Although drain-current transient based methodologies have been used consistently to extract trap parameters, the factors affecting the non-exponential nature of the transient are still not well understood. No effort at accurately replicating multiple deep-levels in the GaN buffer to simulate transient response of GaN based power devices has been reported previously. In this work, we present numerical simulation results of HEMTs having multiple discrete trap states as well as band-like distribution of traps in the GaN band-gap. On-state current of synchronous gate and drain pulsing simulations show current as a sum of stretched multiexponentials, with stretching factor showing trap and Fermi-level dependence. Using this capability incorporated into FLOODS TCAD simulator and definition of deep-levels in the GaN buffer precisely, modeling of non-exponential transients and associated wide peaks in the transient derivatives can be carried out accurately.

Photoluminescence and white light generation behavior of lithium gadolinium silicoborate glasses

The Dy3+-doped lithium gadolinium silica borate glasses with composition (in mol%) 40Li2O:15Gd2O3:5SiO2: (40-x)B2O3:xDy2O3, x = 0.01, 0.1, 0.5, 1.0, 2.0 were prepared by melt quenching technique and characterized through absorption and emission spectra, CIE chromaticity coordinates and decay rate analysis. Judd-Oflet parameters have been calculated for lithium gadolinium silico borate glass and used for the derivation of radiative properties for excited luminescent levels of Dy3+ ions. The feasibility of white light generation have been evaluated by the yellow-to-blue emission intensity ratios and CIE chromaticity coordinates as a function of Dy3+ concentration. The non-exponential decay rates are well-fitted to Inokuti-Hirayama model for S = 6. The perceived non-exponential decay nature and life time quenching have been ascribed to the energy transfer between excited and unexcited Dy3+ ions through dipole–dipole interaction. The CCT values for the present studied glasses obtained in the 4584-4235 K at λexc = 387 nm. These CCT values are below the warm CCT (i.e CCT 4000 K). The reasonably good luminescence properties of LGSiBDy10 glass indicates the potentiality of the title of glass to be applied as lasing medium for white light generation.

Spectroscopic investigations of Nd3+ doped gadolinium calcium silica borate glasses for the NIR emission at 1059 nm

The Nd3+-doped gadolinium calcium silica borate (BSGdCaNd) glasses of composition (55-x) B2O3 - 10 SiO2 - 25 Gd2O3 -10 CaO -x Nd2O3, where x = 0.0, 0.05, 0.5, 1.0, 1.5, 2.0 and 2.5 mol %, have been prepared by conventional melt quenching technique and are characterized through structural, thermal, absorption, emission and decay time measurements. Based on the Judd-Ofelt intensity parameters and radiative properties were determined from the absorption spectrum. The emission spectra recorded for BSGdCaNd glasses gives three emission transitions 4F3/2 → 4I9/2 (903 nm), 4F3/2 → 4I11/2 (1059 nm) and 4F3/2 → 4I13/2 (1334 nm) for which effective bandwidths (Δλeff) and stimulated emission cross-section (σ(λp)) are evaluated. Branching ratios (βR) measured for BSGdCaNd0.5 glass show that 4F3/2 → 4I11/2 transition is quite suitable for lasing applications. The intensity of emission spectra increases with increase in the concentration of Nd3+ ion up to 1.0 mol% and beyond that concentration, quenching is observed. The decay from 4F3/2 level is found to be non-exponential nature for concentrations of Nd3+ ions. The non-exponential curve has been fitted to the Inokuti-Hirayama model to understand the nature of energy transfer process. Hence, the high emission cross-section (1.39 × 10−20 cm2), branching ratio (0.58) and long lifetime (342 μs) indicate that the BSGdCaNd0.5 glass system could be considered as a good candidate for strong NIR lasers at 1059 nm.

On the relation between non-exponential scrape off layer profiles and the dynamics of filaments

A theoretical framework is developed to clarify the relation between the profiles of density and temperature in the scrape off layer (SOL) with the fluctuations (filaments) that generate them. The framework is based on the dynamics of independent filaments and on their statistical behaviour and can be used to rigorously understand the mechanisms that lead to the non-exponential nature of the radial SOL profiles as well as the increase of the relative fluctuation amplitude in the far SOL. Several models for the dynamics of the filaments, which can be applied to the framework, are derived and discussed for the purpose of identifying how different assumptions lead to the emergence of features in the profiles. It is found that multiple alternative models can explain the observations, thus motivating more stringent and focused experimental analysis. In particular, radially accelerating filaments, less efficient parallel exhaust and also a statistical distribution of the velocity of the filaments can all contribute to induce flatter profiles in the far SOL. A quite general result is the resiliency of the non-exponential nature of the profiles. At the same time, several of the models discussed can also capture the increase of the relative fluctuation amplitude observed in the far SOL. It is also shown that several scenarios are compatible with the broadening of the SOL, which could be caused by charge exchange interactions with neutral particles or by a significant radial acceleration of the filaments.

Influence of Modifier Cations on the Spectroscopic Properties of Dy3+ Doped Telluroborate Glasses for White Light Applications.

The effect of electronegativity and ion size of the modifier cations have been analyzed through a new series of Dy3+ doped telluroborate glasses prepared by melt quenching technique with the composition of 30TeO2+29.5B2O3+20MO+20MF2+0.5Dy2O3 (where M=Ba2+, Sr2+, Zn2+, Cd2+ and Pb2+). The various stretching and bending vibrational modes of borate and tellurite network have been identified through FTIR spectral measurements. The conversion of BO3 units into BO4 units increases NBOs in the glass network and the same is confirmed through FTIR spectra. The nephelauxetic ratio ([Formula: see text]) and bonding parameter (δ) value reveals that the Dy-O bond in prepared glasses possesses ionic nature. JO intensity parameters (Ω2, Ω4 and Ω6) of the present glasses follow the trend Ω2>Ω4>Ω6 uniformly in all the prepared glasses. Radiative parameters like transition probability (A), stimulated emission cross section[Formula: see text], branching ratio (βR) values have been predicted from the absorption spectra of Dy3+ ions using JO theory. Among the prepared glasses TBZnD glass posses a better CIE 1931 colour chromaticity coordinates (0.33, 0.39) and CCT value (5019K). Decay profile of 4F9/2 state of the Dy3+ ion exhibits non-exponential nature due to the interaction between Dy3+-Dy3+ ions. The nature of interaction between Dy3+-Dy3+ ions has been analyzed through Inokuti-Hirayama model and the best fit of S=6 indicates that the dipole-dipole interaction is responsible for the energy transfer between Dy3+-Dy3+ ions. The glass containing Zn2+ ions posses encouraging results such as higher Y/B intensity ratio, stimulated emission cross section and higher branching ratio (4F9/2→6H13/2). Thus the present study identified the Zn2+ ions as a better modifier ion to develop the Dy3+ doped glasses for various photonic applications.

Nanocrystalline Sm3+-doped Lu3Ga5O12 garnets: An intense orange-reddish luminescent material for white light emitting devices

Nanocrystalline lutetium gallium garnets Lu3Ga5O12 doped with various concentrations of Sm3+ ions have been prepared by a low-cost and environmentally benign sol–gel method. The nanocrystalline structure of the Lu3Ga5O12 garnets has been identified by X-ray powder diffraction whereas their optical properties have been investigated through laser-excited spectroscopic techniques. The diffuse reflectance spectrum of Sm3+ ions in Lu3Ga5O12 nano-garnets has been measured for predicting its partial energy level structure. The luminescence spectra of Sm3+-doped Lu3Ga5O12 nano-garnets have been measured under both 405 and 473nm laser excitations as a function of Sm3+ ion concentration. The nano-garnets exhibit intense orange-reddish luminescence at 615nm attributed to the 4G5/2→6H7/2 transition. The optimum molar concentration of Sm3+ ions have been found to be about 3.0mol% with critical energy transfer distance of 16.8Å. The luminescence decay curves of the 4G5/2 level of Sm3+ ions measured under 560nm resonant excitation have been found to be non-exponential. The non-exponential nature of the decay curves has been analyzed by Inokuti–Hirayama model and found that the dominant mechanism of interaction between active ions is of dipole–dipole type. All these results indicate that the present nano-garnets could be useful for white light emitting devices.

Biphoton Statistics of Quantum Light Generated on a Silicon Chip

We demonstrate a silicon-chip biphoton source with an unprecedented quantum cross-correlation up to gsi(2)(0) = (2.58 ± 0.16) × 104. The emitted photons are within single whispering gallery mode with self-correlations of gss(2)(0) = 1.90 ± 0.05 and gii(2)(0) = 1.87 ± 0.06 for signal and idler photons, respectively. We observe the waveform asymmetry of cross-correlation between signal and idler photons and reveal the identical and nonexponential nature of self-correlations of individual signal and idler photon modes, which is the nature of cavity-enhanced nonlinear optical processes. The high efficiency and high purity of the biphoton source allow us to herald single photons with a conditional self-correlation gc(2)(0) as low as 0.0059 ± 0.0014 at a pair flux of 1.95 × 105 pairs/s, which remains below 0.026 ± 0.001 for a biphoton flux up to 2.93 × 106 pairs/s with a tunable photon preparation efficiency in the single-mode fiber up to 51% and a raw heralding efficiency up to 3.4%. Our work unambiguously dem...

Structural and luminescent properties of KY(1−x)DyxBO3 phosphors

Yttrium borate phosphors (KY(1−x)DyxBO3) doped with Dy3+ ions were synthesized by the solid-state reaction method. The structural and morphological characteristics were studied by XRD, FTIR and SEM measurements. Luminescent properties of different concentrations of KY(1−x)DyxBO3 phosphors were investigated from the excitation, emission and decay analyses. The emission spectra exhibited characteristic blue (460–500nm) and yellow (555–610nm) bands of Dy3+ ions which combines to give white light. The evaluated color co-ordinates (x, y) were found to lie within the white light region of CIE chromaticity diagram. All the decay curves of Dy3+ ions exhibited non-exponential nature and the experimental lifetimes for the 4F9/2 excited level were found to decrease from 0.87, 0.47, 0.35, 0.26 and 0.13ms with the increase of Dy3+ ion concentrations from 0.05, 0.1, 0.15, 0.2 and 0.3mol%, respectively. In order to understand the energy transfer mechanism, the decay curves were fitted to Inokutti-Hirayama model and found that the energy transfer is of dipole-dipole type. From the results of these investigations, it is concluded that the KY(1−x)DyxBO3 phosphors are more useful for white light emitting diodes.

Effect of Tb3+ concentration on Sm3+ doped leadfluoro-borophosphate glasses for WLED applications

A new series of Sm3+/Tb3 co-doped leadfluoro-borophosphate glasses with the composition 50B2O3+(19.5−x)P2O5+10Li2O+10ZnF2+10PbO+0.5Sm2O3+xTb2O3 (where x=0, 0.05, 0.1, 0.25, 0.5, 1 and 2 in wt%) have been prepared following the melt quenching technique. The presence of fundamental vibrational groups such as BO3, BO4 and PO4 were explored through the FTIR and Raman spectral measurements. The nephelauxetic effect on the absorption transitions have been used to elucidate the bonding nature of the Sm3+ ions with the surrounding ligands thus reveal the predominant ionic nature. Effect of Tb3+ ions on the symmetry of the ligand field around the Sm3+ ions have been predicted using asymmetric intensity ratio values. It is observed that asymmetry around the Sm3+ ion increases with Tb3+ ion concentration upto 1wt% due to the chaos of both the rare earth ions and after that Tb3+ ion concentration dominates thus in-turn creates lower asymmetrical environment. Luminescence quenching effect due to the presence of RE3+ ions concentration has never seen upto almost 2.5wt% (for both RE ions) hence the present host possess the capability to incorporate more number of RE ions. The decay profile of the Tb3+ ion (5D4) is found tobe single exponential and Sm3+ ion (4G5/2) is found to be non-exponential nature. The decreasing trend in the experimental lifetime value of the Tb3+ ions confirms the energy transfer process takes place from Tb3+ ions to Sm3+ ions and the interaction takes place between Tb3+ and Sm3+ ions is of dipole-dipole nature and the same is analyzed using IH model. The energy transfer efficiency is found to increase from 47% to 54% with Tb3+ ion concentration. The CIE color chromaticity coordinates have been calculated to identify the characteristic emission of the prepared glasses and the correlated color temperature, color purity were also determined. All these results suggest that, BPLS0.5T glass is a potential candidate for warm white light applications with minimal blue hazards.

Structural and optical investigations on Dy3+doped lithium tellurofluoroborate glasses for white light applications

Dy3+doped lithium tellurofluoroborate glasses were prepared with the chemical composition (40–x)B2O3+15TeO2+15Li2O+15LiF+15NaF+xDy2O3 (BTLNxD; where x=0.05, 0.1, 0.25, 0.5, 1.0 and 2.0 in wt%) following conventional melt quenching technique and characterized through FTIR, optical absorption, luminescence and lifetime measurements. The vibrations of the borate and tellurite network have been identified through FTIR spectral measurements. The optical properties have been explored from the absorption and luminescence spectra. The optical band gap of direct and indirect allowed transitions was determined from Tauc׳s plot and the variations in the band gap energy with structural arrangements in the prepared glasses is also discussed. Judd–Ofelt theory has been used to evaluate the intensity parameters Ω2, Ω4 and Ω6 using the experimental oscillator strengths and absorption energy levels. The radiative parameters such as transition probability (A), stimulated emission cross-section (σPE), branching ratios (βR) and radiative lifetime (τR) corresponding to the 4F9/2→6H11/2, 6H13/2 and 6H15/2 emission transitions were calculated from the luminescence spectra. The yellow-to−blue (Y/B) luminescence intensity ratios and colour chromaticity coordinates of the title glasses have also been estimated to evaluate the white light emission as a function of Dy3+ion concentration. These results have been used to identify the suitability of the prepared glasses for W-LED applications. The decay rates for the 4F9/2 level have been measured and found to deviate from exponential to non-exponential nature with the increase of Dy3+ion concentration. The non-exponential decay rates have been fitted with the Inokuti–Hirayama model for S=6 which indicate that dipole–dipole mechanism is responsible for the energy transfer processes through Dy3+–Dy3+interaction.

Optical and structural investigation of dysprosium doped-Y2Te4O11

In this paper, the optical properties of Y2Te4O11 microcrystalline powders doped with Dy3+ ions, ranging between 0.01 and 5.0at%, are reported. The powders were successfully synthesized by the solid state reaction method. Absorption (300K), excitation (300K) and fluorescence spectra (at 11.6 and 300K) as well as fluorescence decay curves recorded at room temperature are presented and analyzed in details. Oscillator strengths, phenomenological Ωλ (λ=2, 4, 6) Judd-Ofelt parameters, radiative transition probabilities, branching ratios, the radiative lifetime of the 4F9/2 level as well as the stimulated emission cross-section for the 4F9/2→ 6H13/2 transition have been determined. The observed non-exponential decay nature and concentration quenching of the 4F9/2 emitting level of the Dy3+ ion, have been attributed to cross-relaxation processes. The high value of the stimulated emission cross-section for the 4F9/2→ 6H13/2 transition at 576.6nm, equal to 0.756×10−20cm2, indicates that Y2Te4O11 activated by trivalent dysprosium ions is an attractive candidate for a solid-sate laser.