Observed Emission Transitions Research Articles

Influence the host lattices on photoluminescent properties of the Ce/Tb doped CaF2, NaYF4, and NaGdF4 nanoparticles

Ce3+/Tb3+ ions doped CaF2, NaYF4, and NaGdF4 nanoparticles (NPs) were prepared by the EDTA chelating-based thermal decomposition process. X-ray diffraction (XRD) profile shows the cubic phase in CaF2 and NaYF4 host lattice, whereas NaGdF4 in hexagonal phase, highly crystalline with an average grain size is estimated to be 20, 10, and 25 nm, respectively. Fourier transforms infrared (FTIR) spectra were employed to determine the superficial chemistry of the metal fluoride NPs. UV/Visible spectra measured in H2O solution exhibited good optical properties, and excellent colloidal stability of the luminescent NPs, implying the surface-attached organic moieties. Optical bandgap energies were estimated to determine the optical performance of the NPs. The excitation and emission spectra revealed the good photoluminescence properties of the respective host matrices. In a comparative analysis, CaF2:Ce/Tb NPs host lattice revealed efficient charge transmission from Ca2+ to the activator Tb3+ resulting in observed emission transitions of the Tb3+-ions are remarkably high luminescence efficiencies. The lifetime estimated for the Ce3+/Tb3+-doped CaF2, NaYF4, and NaGdF4 NPs is found to be 7.32, 4.169, and 4.81 ms, respectively. These findings show that the synthesized luminescent NPs presented novel luminescent properties in which CaF2:Ce/Tb NPs produce remarkable crystallinity and photoluminescent properties to be highly useful in fluorescent-based biomedical and technological applications.

Luminescence behaviour and phonon sideband analysis of europium doped Bi2O3 based phosphate glasses for red emitting device applications

0.5 mol% of europium (Eu3+) doped bismuth phosphate glasses (BiP) with different contents (0, 5, 10 and 15 mol%) of bismuth and different (0.1, 0.3, 0.5, 1.0, 1.5 and 2.0) mol% of Eu3+ doped 5 mol% bismuth contained BiP glasses were made by melt-quenching technique. The structural and photoluminescence properties were analysed via FT-Raman, excitation, luminescence and decay time computations. Judd-Ofelt (J-O) parameters were evaluated from the emission spectra and also various radiative properties such as radiative transition probabilities (AR), radiative lifetimes (τrad), stimulated emission cross-sections (σe), branching ratios (β), optical gain bandwidths (σexΔλeff) and optical gain (σexτrad) values for the observed emission transitions are studied. The electron-phonon coupling constants (g), phonon energies (hω) and the multiphonon relaxation rates (WMPR) were determined. The decay curves of 5D0 level of Eu3+ in all the studied glasses exhibit single exponential nature. The lifetimes are obtained from the decay curves and reported. The CIE chromaticity co-ordinates were computed and they have fallen in red region. The characteristic red luminescence emission around 612 nm for 5D0→7F2 transition confirmed that the Eu3+ doped BiP glasses might be useful to fabricate red lasers and display devices.

Investigations on the spectroscopic properties and local structure of Eu3+ ions in zinc telluro-fluoroborate glasses for red laser applications

The strong red emitting Eu3+ doped Zinc telluro-fluoroborate glasses with the chemical composition (30–x)B2O3+30TeO2+16ZnO+10ZnF2+7CaF2+7BaF2+xEu2O3 (where x = 0.1, 0.25, 0.5, 1.0, 2.0 and 3.0 in wt%) have been prepared following the melt-quenching technique and their structural, spectroscopic behavior were characterized. The local structure and vibronic spectral analysis were performed in order to correlate them with the local field environment of Eu3+ ions in the prepared Zinc telluro-fluoroborate glasses on the basis of FTIR, Raman, Phonon sideband spectroscopy. Fundamental stretching units of Te–O bond in TeO3/TeO4 units, stretching of B–O bond in BO3/BO4 units and bending vibrations of Te–O–Te/B–O–B bonds were identified through FTIR and Raman spectral analysis. The Nephelauxetic intensity ratios (β) and bonding parameter (δ) values obtained from the absorption bands reveals the covalent nature of the Eu–O bond in the prepared glasses. Phonon sidebands appear around 505, 732 and 999 cm−1 results from the combined bending vibrations of Zn−O−Te and Te−O−Te in borate network, combined stretching vibrations of TeO4 trigonal bipyramidal (tbp) units with the formation of vitreous B2O3 due to the bending vibration of B–O–B linkages, and B−O bond stretching in BO4 units, stretching modes of terminal oxygens (B–O−) belong to the BO2O metaborate triangles respectively. The JO intensity parameters (Ωλ) and the asymmetric intensity ratio (R) values calculated from the emission spectra have been used to explore the nature of the bonding and asymmetry around the Eu-ligand field environment. The increasing Ω2 intensity parameters and R values confirms the higher asymmetry around the Eu3+ ions and covalency of Eu–O. The JO intensity parameters were used to estimate the radiative properties such as transition probability (A), stimulated emission cross-section (σPE), branching ratio values (β) and radiative lifetimes (τR) for the observed emission transitions. The excited state lifetime for the 5D0 level of the Eu3+ ions exhibit single exponential behavior for all the titled glasses and found to increase with the increase in Eu3+ ions concentration due to the higher asymmetry around Eu3+ ions. Further, emission intensities were characterized using CIE chromaticity diagram and the (x,y) chromaticity coordinates (0.63, 0.36) suggests the pure intense red emission obtained from the prepared glasses useful for laser applications at 616 nm.

Luminescence properties and quantum efficiency of the Eu-doped borate glasses

The luminescence and radiative properties of the Eu-doped borate glasses with Li2B4O7, CaB4O7, and LiCaBO3 basic compositions have been investigated and analysed. The borate glasses of high chemical purity and optical quality, doped with Eu2O3 in amounts of 0.5 and 1.0 mol. % were obtained from the corresponding polycrystalline compounds in the air atmosphere using standard glass synthesis technology. The spectroscopic and radiative properties of obtained Eu-doped glasses were studied using electron paramagnetic resonance (EPR), optical absorption, photoluminescence (excitation and emission spectra, decay kinetics) techniques, and modified Judd–Ofelt analysis. The photoluminescence spectra of the Eu-doped borate glasses reveal intense emission bands, which correspond to the 5D0 → 7FJ (J = 0 ÷ 4) transitions of Eu3+ ions. The observed luminescence decay curves are satisfactory described in the framework of single exponential approximation with lifetimes, which lie in the 2.04 ÷ 2.26 ms range. The Judd–Ofelt intensity parameters (Ωλ) for Eu3+ centres in the investigated glasses were calculated from their luminescence emission spectra. Radiative lifetimes and internal quantum efficiencies were estimated for observed emission transitions of the Eu3+ centres in the investigated glasses. External quantum yield of luminescence was measured experimentally via an absolute method. The high calculated internal quantum efficiency (∼50%) and relatively high measured external quantum yield (∼11%) of the Eu3+ luminescence show that the Li2B4O7:Eu, CaB4O7:Eu, and LiCaBO3:Eu glasses belong to perspective luminescent materials.

Structural and luminescence properties of Dy3+ doped bismuth phosphate glasses for greenish yellow light applications

Different compositions of (5, 10, 15 and 20 mol%) of bismuth and different concentrations (0.5, 1.0, 1.5 and 2.0 mol%) of Dy3+ ion doped bismuth phosphate (BiP) glasses were synthesized by melt-quenching technique. The structural characterization was accomplished by XRD, SEM with EDS, FTIR, FT-Raman and 31P MAS NMR spectroscopy. The optical properties were studied using absorption and photoluminescence spectroscopy. Different structural groups were identified using FTIR and FT-Raman spectra. The depolymerization of metaphosphate chains are described by the decrease of Q2 tetrahedral sites allowing the formation of pyrophosphate groups (Q1) revealed by 31P MAS NMR spectroscopic investigations.Judd-Ofelt intensity parameters Ωλ (λ = 2, 4 and 6) were evaluated from absorption spectra. Radiative parameters such as radiative lifetimes (τR), integrated absorption cross-sections (Σ) and branching ratios (βR) were calculated using Judd-Ofelt intensity parameters. From photoluminescence spectra, experimental branching ratios (βexp) and stimulated emission cross-sections (σP) were calculated for all the observed emission transitions of prepared glasses. The decay profiles for 4F9/2 level were recorded and fit exponential for 0.5 mol% and non-exponential for higher concentrations of Dy3+ due to non-radiative energy transfer among excited Dy3+ ions. The CIE chromaticity co-ordinates have been calculated from the luminescence spectra which confirmed greenish yellow light emission.

Spectroscopy of the Er-doped lithium tetraborate glasses

The electron paramagnetic resonance (EPR), optical absorption, and luminescence (emission and excitation) spectra as well as luminescence kinetics of the Er-doped glasses with Li2B4O7 composition were investigated and analysed. The high optical quality glasses with Li2B4O7:Er composition containing 0.5 and 1.0mol.% Er2O3 were obtained from corresponding polycrystalline compound by standard glass synthesis. The EPR spectroscopy in the 4.2–300K temperature range and optical spectroscopy at 300K show that the Er impurity is incorporated into the network of Li2B4O7 glass as Er3+ (4f11, 4I15/2) ions, exclusively. The local structure of the Er3+ luminescence centres in Li sites of the glass network is proposed. Based on the standard Judd–Ofelt theory the oscillator strength (Pcal) and experimental oscillator strength (Pexp) for observed absorption transitions as well as phenomenological intensity parameters (Ω2, Ω4, Ω6) for Er3+ centres in the Li2B4O7:Er glass containing 1.0mol.% Er2O3 were calculated. Spectroscopic parameters of relevance for laser applications, including emission probabilities of transitions (Wr), branching ratios (β), and radiative lifetime (τrad) have been calculated for main observed emission transitions of the Er3+ centres in Li2B4O7:Er glasses. Experimental and calculated lifetimes were compared and quantum efficiency (η) for green (4S3/2→4I15/2 transition) and infrared (4I13/2→4I15/2 transition) emission bands has been estimated.

Radiative properties and luminescence spectra of Sm3+ ion in zinc–aluminum–sodium-phosphate (ZANP) glasses

The fluorescence properties of different concentrations of Sm3+ doped zinc–aluminum–sodium-phosphate (ZANP) glasses were studied by the XRD, SEM, FTIR, TG–DTA, optical absorption, photoluminescence and decay cure analysis. X-ray diffraction profiles and SEM images confirmed the amorphous nature of the glass samples. Structural information of these glass matrices was provided by FTIR spectrum. Judd–Ofelt (J–O) theory was applied to the experimental oscillator strengths to evaluate three phenomenological J–O intensity parameters, Ωλ (λ=2, 4 and 6). Using J–O intensity parameters and emission spectra, various radiative parameters such as radiative transition probabilities (AR), radiative lifetimes (τR), calculated and measured branching ratios (βR and βm), effective bandwidths (Δλeff) and stimulated emission cross-sections (σP) were calculated for observed emission transitions. The intensity of emission transitions with the variation of Sm3+ ion concentration was studied. The nature of decay curves of 4G5/2 level for different Sm3+ ion concentrations in ZANP glass was analyzed and obtained measured lifetimes (τexp). Quantum efficiency of 4G5/2 level was calculated based on experimental and measured radiative lifetimes (τexp and τR).

Lasing potentialities and white light generation capabilities of Dy3+ doped oxy-fluoroborate glasses

Oxy-fluoroborate (OFB) glasses doped with different concentrations of Dy3+ ions were synthesized through melt quenching technique and characterized by using optical absorption, photoluminescence and decay analysis to understand the lasing potentialities and their utility for white light emitting diodes (LEDs). The XRD spectrum recorded for undoped OFB glass confirms the amorphous nature of the prepared glasses. Judd–Ofelt theory has been applied to the recorded absorption spectra to measure the radiative properties such as transition probability (AR), radiative lifetimes (τR), branching ratios (βR) and spectroscopic quality factor (χ) for the prominent fluorescent levels. The emission spectra recorded for these glasses gives four emission transitions 4F9/2→6H15/2, 6H13/2, 6H11/2 and 6H9/2 for which effective band widths (ΔλP), experimental branching ratios (βexp) and stimulated emission cross-sections (σse) are evaluated. To know the lasing potentialities of these glasses, the quantum efficiency (η) of these glasses are measured by recording the decay curves for the prominent emission levels 4F9/2→6H15/2 and 4F9/2→6H13/2. Among the observed emission transitions, a transition at 575nm (4F9/2→6H13/2) indicates the lasing potentialities. The CIE chromaticity co-ordinates and the confocal photoluminescence images of these glasses further suggests the near white light generation capabilities in principle.

Ho3+‐doped strontium–aluminium–bismuth–borate glasses for green light emission

Strontium-aluminium-bismuth-borate glasses (SAlBiB) doped with different concentrations of Ho(3+) were prepared using conventional melt quenching technique and their structural and optical properties investigated. X-ray diffraction and scanning electron microscopy analysis were used to study the structural properties. Optical properties were studied by measuring the optical absorption and visible luminescence spectra. The Judd-Ofelt (J-O) theory was applied to evaluate J-O intensity parameters, Ω(λ) (λ = 2, 4 and 6). Using J-O intensity parameters, radiative properties such as spontaneous transition probabilities (A(R)), branching ratios (β(R)) and radiative lifetimes (τ(R)) were determined. From the emission spectra, a strong green emission nearly at 549 nm corresponding to the transition, (5)S2 ((5)F4)→(5)I(8) was observed. Emission peak positions (λ(P)), effective bandwidths (Δλ(eff)) and stimulated emission cross-sections (σ(p)) were calculated for the observed emission transitions, (5)F3 →(5)I(8), (5)S2((5)F4)→(5)I(8) and (5)F5 →(5)I(8) of Ho(3+) in all the glass matrices. Chromaticity color coordinates were calculated using the emission spectra. The experimental results suggest that SAlBiB glass matrix with 1.5 mol% of Ho(3+) has better emission properties.

Investigations on luminescence performance of Sm3+ ions activated in multi-component fluoro-phosphate glasses

Different metal oxide based fluoro-phosphate glasses doped with Sm3+ ions are investigated using XRD, SEM with EDS, FTIR, Raman spectra, optical absorption and photo-luminescence techniques. These glass matrices have been prepared by conventional melt quenching technique. The glassy nature of the present glass matrices are confirmed by XRD profiles and SEM photographs. The composition of the glasses is checked by EDS. Based on FTIR and Raman spectra, the authors have analyzed functional groups that are present in the glass matrices. Judd–Ofelt intensity parameters, Ωλ (λ=2,4,6) have been evaluated from absorption spectra. Radiative parameters such as radiative transition probabilities (AR), radiative lifetimes (τR), integrated absorption cross sections (Σ) and branching ratios (βR) are calculated using Judd–Ofelt intensity parameters. From the photoluminescence spectra, experimental branching ratios (βexp) and stimulated emission cross-sections (σP) for all the observed emission transitions are calculated. To investigate luminescence potentiality of 4G5/2→6H7/2 emission level of Sm3+ doped different fluorophosphate glasses, experimental radiative lifetimes (τexp) are obtained from decay curve analysis for all glass matrices. Finally, these observed results are discussed and compared with the literature data.

Thermal and optical properties of Nd3+ doped lead zinc borate glasses—Influence of alkali metal ions

In the present investigation a new series of six different Nd3+ doped alkali and mixed alkali (Li, Na, K, Li–Na, Li–K and Na–K) heavy metal (PbO and ZnO) borate glasses were prepared using the melt quenching technique. The amorphous nature of the glass systems has been identified based on the X-ray diffraction analysis. The glass transition studies were carried out using differential scanning calorimetry (DSC). Optical properties were studied by measuring the optical absorption and near infrared luminescence spectra. The Judd–Ofelt (J–O) theory has been applied to calculate J–O intensity parameters, Ωλ (λ=2, 4 and 6) and in turn used to estimate radiative properties of certain transitions. Spectroscopic parameters such as transition probabilities (AT), branching ratios (β), radiative lifetimes (τR) and integrated absorption cross-sections (Σ) were calculated using J–O intensity parameters for all transitions. Using emission spectra, experimental branching ratios and stimulated emission cross-sections (σP) are obtained for all the observed emission transitions.

Spectroscopic investigations on Pr3+ and Nd3+ doped strontium–lithium–bismuth borate glasses

Spectroscopic investigations on different concentrations (0.1, 0.5, 1.0, 1.5 and 2.0mol%) of Pr3+ and Nd3+ doped strontium lithium bismuth borate glasses have been done. X-ray diffraction, SEM with EDS, absorption and luminescence spectra were recorded for all the glass matrices and analyzed. X-ray diffraction profiles and SEM images conformed amorphous nature of investigated glass samples. EDS spectra of host glass and Pr3+doped glass matrices gave information about the chemical composition of glass samples. From the absorption spectra of Pr3+ and Nd3+ ions, Judd–Ofelt (J–O) intensity parameters (Ωλ,λ=2, 4 and 6) have been calculated and compared with other glass matrices. The emission characteristics such as radiative lifetimes (τR), measured and calculated branching ratios (β) and stimulated emission cross-sections (σP) have been obtained for the observed emission transitions of Pr3+ and Nd3+ ions in the above glass matrix for all the concentrations. From the emission spectra of Pr3+ and Nd3+ doped glass matrices, the effect of concentration on the quenching of intensity of 1D2→3H4 transition of Pr3+ ion and 4F3/2→4I9/2, 4I11/2 and 4I13/2 transitions of Nd3+ have been studied and discussed.

Citric based sol-gel synthesis and photoluminescence properties of un-doped and Sm 3+ doped Ca 3Y 2Si 3O 12 phosphors

The photoluminescent properties of un-doped and Sm 3+ doped Ca 3Y 2Si 3O 12 phosphors were prepared by the citrate sol-gel method. Un-doped sample has shown a strong blue emission, which has its maximum intensity at 389 nm. Among all the observed emission transitions 4G 5/2→ 6H J (J = 5/2, 7/2 & 9/2) of Sm 3+, the reddish-orange (RO) emission transition 4G 5/2→ 6H 7/2 is more prominent, which matches well with the emission wavelength of near UV (n-UV) LED. The reasons for the observance of such prominent visible color emissions from these phosphors have been substantiated appropriately. Besides, structural details of these samples have also been analyzed from the measured XRD, TEM, TG-DTA and FT-IR profiles.

Studies on optical absorption and photoluminescence properties of Pr 3+ and Nd 3+ doped mixed alkali chloroborate glasses

This article presents the optical absorption and emission properties of Pr 3+ and Nd 3+ doped two different mixed alkali chloroborate glass matrices of the type 70B 2O 3· xLiCl·(30 − x)NaCl and 70B 2O 3· xLiCl·(30 − x)KCl ( x = 5, 10, 15, 20 and 25). The variation of Judd–Ofelt parameters ( Ω 2, Ω 4 and Ω 6), total radiative transition probabilities ( A T), radiative lifetimes ( τ R) and emission cross-sections ( σ p) with the variation of alkali contents in the glass matrix have been discussed in detail. The changes in the peak wavelengths of the hypersensitive transition and intensity parameters with x are correlated to the structural changes in the host matrix. The estimated radiative lifetimes of certain excited states of Pr 3+ and Nd 3+ in these two glass matrices are reported. Peak stimulated emission cross-sections ( σ P) are reported for the observed emission transitions of Pr 3+ and Nd 3+ ions. Branching ratios ( β) of the observed emission transitions obtained from the Judd–Ofelt theory are compared with the values obtained from the emission spectra.

Spectroscopy of Pr 3+ ions in lithium borate and lithium fluoroborate glasses

Optical absorption and emission spectra of 1 mol% Pr 3+ doped lithium borate and lithium fluoroborate glasses have been recorded. The intensities of f–f transitions are parameterized in terms of Judd–Ofelt (JO) intensity parameters Ω λ ( λ=2, 4 and 6). The JO parameters obtained with modified JO theory have been used to predict radiative properties such as spontaneous emission probabilities ( A), lifetimes ( τ R) and branching ratios ( β R) for all the 12 excited states of these Pr 3+ doped glasses along with some of the reported Pr 3+ : systems. The predicted β R are compared with the experimental values for the emission from 3P 0 and 3P 1 levels. The stimulated emission cross-sections are also evaluated for all the observed emission transitions. The β R values for the potential laser transitions including the 1G 4→ 3H 5 (1.3 μm) transition useful for fibre amplifier have been compared for 17 Pr 3+ : systems. The effect of compositional changes of the glasses on the optical properties of Pr 3+ ions have been discussed.

Nature of excited helium atoms in liquid helium: A theoretical model

A model is developed in which excited helium atoms in liquid helium may exist in stable cavities of diameter 10 \AA{} and larger. A repulsive effective interaction between the excited atom and the remaining atoms in the ground state is responsible for cavity formation. The equilibrium shape of the cavity is determined by minimizing the total energy, which is the sum of the electronic perturbation due to the surrounding liquid and the energy required to form the cavity. Each of these can be evaluated separately as a function of the cavity size and shape. The energy required to form a near-spherical cavity of radius $R$ is approximated by the classical expressions for work done against the surface tension $\ensuremath{\gamma}$ of liquid helium, and against the external pressure $p$ on the liquid. For a particular cavity size, the liquid may be represented by a perturbing potential, and the response of the electronic wave function explicitly determined using the variational method. The calculations indicate that the optical spectra of helium atoms in these cavities are only slightly perturbed, and agreement with observed spectra lends strong support to the cavity model. Agreement has been obtained with the observed emission transitions $2^{3}P\ensuremath{\rightarrow}2^{3}S$ and $3^{1,3}S\ensuremath{\rightarrow}2^{1,3}P$, and also with the absorption $2^{3}S\ensuremath{\rightarrow}2^{3}P$, at saturated vapor pressure. Recently, the pressure dependence of the position and width of these spectral lines has been measured up to 25 atm. The pressure dependence predicted by the model is in good agreement with the data for all lines in which the initial state is spherically symmetric.