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This paper reports on the preparation and systematic analysis of energy transfer mechanisms in Nd(3+)-Yb(3+)-Er(3+) co-doped new series of barium-alumino-metaphosphate glasses. The time resolved fluorescence of Nd(3+) in triply doped Ba-Al-metaphosphate glasses have revealed that, Yb(3+) ions could function as quite efficient bridge for an energy transfer between Nd(3+) and Er(3+) ions. As a result, a fourfold emission enhancement at 1.54 mum of Er(3+) ions has been achieved through an excitation of (4)F(5/2) level of Nd(3+) at 806 nm for the glass having 3 mol% Yb(3+) with an energy transfer efficiency reaching up to 94%. Decay of donor (Nd(3+)) 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 approximately 6) interactions are found to be responsible for the occurrence of energy transfer process in theses glasses.

Multivalent Ce/Eu/Tb singly doped along with (Ce-Eu) and (Ce-Tb) dual doped alkali-free Ba-Al metaphosphate glasses are prepared by the melt quenching technique and the results of an investigation of the energy transfer dynamics among dopant ions in this host are reported. The alkali free metaphosphate glass matrix facilitated the in situ formation of divalent europium (Eu2+) due to its reducing nature which played a key role in bringing about a difference in Ce3+ sensitization to Eu3+ and Tb3+ ions respectively. In Eu singly doped glass, a radiative energy transfer has been realized from Eu2+ to Eu3+ ions. Whereas in (Ce3+-Eu3+) co-doped glass series, the presence of cerium promotes oxidation of Eu2+ to Eu3+ with simultaneous reduction of Ce4+ to Ce3+ as the Eu2O3 concentration increases. In case of (Ce3+-Tb3+) co-doped glasses, Tb4+ ion formation with an increase of Tb2O3 content has been seen without any change of the Ce3+ content. All these changes have been interpreted and their impact on the energy transfer dynamics has been thoroughly discussed based on the energy level overlap among the dopant ions. The measured quantum yields (QY) of Eu3+ and Tb3+ ions in singly doped glasses are 78% and 83%, respectively, and compared with other host materials. The effective energy transfer of Ce3+Æ Tb3+ in the present host makes it a promising material as a UV to visible frequency downshifter for solar cell applications. [ABSTRACT FROM AUTHOR]

Abstract: Phonon assisted non-resonant energy transfer from Nd3+→Yb3+ is reported in a new series of heavy metal oxide based zinc–boro–bismuthate glasses. An intense infrared emission at around 1μm from Yb3+ has been realized upon Nd3+ excitation, with a transfer efficiency reaching up to 87% for fairly low acceptor concentration of 1mol% Yb2O3. Such high energy transfer efficiency despite poor spectral overlap of donor’s emission with acceptor''s absorption has been attributed to the excellent matching of host phonon energy with the energy difference among Nd3+ and Yb3+ excitation levels. From the host assisted spectral overlap function, the microscopic energy transfer parameter (C DA ) for Nd3+→Yb3+ energy transfer in these glasses have been estimated and is found to be ∼3.6×10−39 cm6 s−1, which is in good agreement with the C DA value obtained from decay analysis of donor luminescence. The measured fluorescence decay curve showed excellent correlation with the theoretical fit simulated using hopping model suggesting the hopping migration assisted energy transfer. A comparison of the obtained results with other reported host systems has been presented using a performance parameter (Φ ET ) defining the ability of Nd3+→Yb3+ energy transfer per unit loss occurred due to Nd3+–Nd3+ self-quenching. [Copyright &y& Elsevier]

Abstract: A detail investigation on laser spectroscopic properties as a function of Nd3+ ions concentration in a new heavy metal oxide based Zinc–Boro–Bismuthate glasses is reported. The Judd–Ofelt analysis indicated an enhancement in Nd–O bond covalency as well as the local asymmetry of active ions on increase in dopant concentration from 0.1 to 1.5 mol%. Based on the Judd–Ofelt intensity parameters, several radiative properties such as transition probability, radiative lifetime, branching ratio and stimulated emission cross-section of Nd3+ ions have been derived. The luminescence intensity has showed a strong increase up to 0.5 mol% Nd2O3, which then attains maximum at 1 mol% and falls down for further increase in dopant concentration. The luminescence quenching behavior at higher dopant concentration has been attributed to the hopping migration assisted energy transfer mechanism leading to the cross-relaxation among active ions. The energy transfer micro-parameters for cross-relaxation (C DA ) and donor energy migration (C DD ) have been derived from the luminescence decay analysis as well as spectral overlap function respectively. The high stimulated emission cross-section and smaller cross-relaxation micro-parameters along with high quantum yield from the present glasses suggests their potential for compact infrared lasers and waveguide applications. [Copyright &y& Elsevier]

Abstract: An intense NIR emission at 1.57μm is reported in a newly synthesized Yb3+–Er3+ codoped Zinc-borobismuthate glasses. The energy transfer efficiency is found to be 78% for 1mol% Yb2O3 and 0.5mol% Er2O3 concentrations. The transfer process follows a static energy transfer mechanism at a low donor concentration (0.1mol%); whereas, it gets accelerated by donor energy migration at 1mol% Yb2O3. In this glass system, the energy back-transfer has found to be negligible from estimated critical interaction distances for direct (Yb3+ →Er3+) and back (Yb3+ ←Er3+) energy transfer phenomena. The observed efficient NIR emission at 1.57μm has been explained based on the effective energy transfer from Yb3+ ions accompanied by rapid depopulation of 4I11/2 excited level of Er3+ ions through non-radiative multi-phonon relaxation processes, which has also restricted the excited state absorption (ESA) from this level leading to no upconversion suggesting the potentiality of present glass host for proficient NIR luminescence. [Copyright &y& Elsevier]

Europium doped glass-ceramics containing BaF nano-crystals have been prepared by using the controlled crystallization of melt-quenched glasses. X-ray diffraction and transmission electron microscopy have confirmed the presence of cubic BaF nano-crystalline phase in glass matrix in the ceramized samples. Incorporation of rare earth ions into the formed crystalline phase having low phonon energy of 346 cm has been demonstrated from the emission spectra of Eu ions showing the transitions from upper excitation states D (J = 1, 2, and 3) to ground states for the glass-ceramics samples. The presence of divalent europium ions in glass and glass-ceramics samples is confirmed from the dominant blue emission corresponding to its 5d-4f transition under an excitation of 300 nm. Increase in the reduction of trivalent europium (Eu) ions to divalent (Eu) with the extent of ceramization is explained by charge compensation model based on substitution defect mechanisms. Further, the phenomenon of energy transfer from Eu to Eu ion by radiative trapping or re-absorption is evidenced which increases with the degree of ceramization. For the first time, the reduction of Eu to Eu under normal air atmospheric condition has been observed in a BaF containing oxyfluoride glass-ceramics system. [ABSTRACT FROM AUTHOR]

An investigation of donor-acceptor energy transfer kinetics in dual rare earths doped precursor oxy-fluoride glass and its glass-ceramics containing NaYF4 nano-crystals is reported here, using three different donor-acceptor ion combinations such as Nd-Yb, Yb-Dy, and Nd-Dy. The precipitation of NaYF4 nano-crystals in host glass matrix under controlled post heat treatment of precursor oxy-fluoride glasses has been confirmed from XRD, FESEM, and transmission electron microscope (TEM) analysis. Further, the incorporation of dopant ions inside fluoride nano-crystals has been established through optical absorption and TEM-EDX analysis. The noticed decreasing trend in donor to acceptor energy transfer efficiency from precursor glass to glass-ceramics in all three combinations have been explained based on the structural rearrangements that occurred during the heat treatment process. The reduced coupling phonon energy for the dopant ions due to fluoride environment and its influence on the overall phonon assisted contribution in energy transfer process has been illustrated. Additionally, realization of a correlated distribution of dopant ions causing clustering inside nano-crystals has also been reported. [ABSTRACT FROM AUTHOR]

Abstract: Yb3+–Ho3+: co-doped and Yb3+: singly doped tellurite glasses prepared by conventional melt quenching technique were studied for their sensitised NIR to vis-upconversion performance. The oscillator strength of an absorption transition of the sensitizer (Yb3+) ions was calculated by using the smakula equation from the base glass corrected absorption spectra of Yb3+ singly doped glass. A bright green upconversion emission of Ho3+ ions from the co-doped glass upon exciting Yb3+ ions with 980nm laser diode and a simultaneous 12 fold decrease in 1.008μm emission intensity of Yb3+ ions has been attributed to the energy transfer from sensitizer (Yb3+) to the acceptor (Ho3+) ions. Donor, Yb3+ ion decay kinetics has been analysed by considering Inokuti–Hirayama and Burshtein theoretical models and confirmed the donor–donor hopping migration assisted energy transfer among Yb3+–Ho3+. The energy transfer efficiency estimated from the experimental lifetimes of the singly doped and co-doped system was found to be 85.8%. Further, the upconversion spectra recorded by varying the pump laser power revealed a two photon contribution for the green and red upconversion emission process with the prevalence of saturation. The phenomena of upconversion emissions in the co-doped system were explained with the partial energy level diagram. This glass has been found to be a promising material for the development of solid state upconversion green emitting laser. [Copyright &y& Elsevier]

Abstract: 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 7Fj ground state multiplet, respectively. The glass with 2wt% of Tb2O3 has exhibited maximum intensity of blue emission from 5D3 level, while green emission from 5D4 level has increased linearly up to 24wt% and showed reduction in the rate of increase for higher Tb2O3 concentrations. The concentration quenching of blue emission (5D3→7Fj) 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→7Fj) 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. [Copyright &y& Elsevier]

Luminescence characteristics and energy transfer dynamics have been studied in a series of Ce-Eu co-doped and Ce-Eu-Tb triply doped zinc fluoroboro silicate glasses to achieve white light generation for LED applications. In this host, Eu ions are found to exist substantially in divalent state (Eu 2+ ) rather than in trivalent state (Eu 3+ ) which has been verified through XPS studies. Further presence of Ce 3+ in co-doped samples aids in the reduction process of Eu 3+ →Eu 2+ . In Ce-Eu co-doped glass series, the Ce 3+ sensitized luminescence realized from Eu 3+ has been ascribed to the electron transfer process between Ce 3+ and Eu 3+ . Inclusion of Tb 3+ resulted in enhancement of Eu 3+ emission in triply doped glasses due to effective energy transfer from Tb 3+ to Eu 3+ . Chromaticity co-ordinates calculated using CIE diagram resulted in realization of warm white light (x = 0.38, y = 0.39; CCT∼ 4116 K) from the triply doped glasses under excitation at 378 nm which can prove to be beneficial for lighting living rooms. [ABSTRACT FROM AUTHOR]

The aim of the present work is to show a simple quantitative theoretical study on the relaxation mechanisms of the 4F 3/2 levels of the Nd3+ ions in the widely used meta-phosphate laser glass system (P 2 O 5 –Al 2 O 3 –BaO–K 2 O) for the studied concentration range of the Nd3+ ions from 0.10 × 1020 to 8.15 × 1020 ions/cm3. Auzel's diffusion-limited model for energy transfer has been adopted in the present study for estimating zero concentration level lifetime, τ 0 of 4F 3/2 levels in the Nd3+ ions present in the studied glass matrix. Primarily, the relaxation mechanisms are dominated by radiative decay (k rad) and energy transfer to hydroxyl groups (k OH) present in the glass network structure up to the dopant, Nd3+ concentration 0.78 × 1020 ions/cm3. Later on, with increasing dopant ion concentration, fluorescence from trivalent Nd3+ ions is unfortunately quenched by the interaction between Nd3+ ions, also known as concentration quenching. The concentration quenching of the fluorescence lifetime has been analysed using proposed Inokuti-Hirayama (I–H), Yokota-Tanimoto (Y-T) and Brushtein (B) models and found to be migration-assisted cross-relaxation mechanisms at or beyond 1.47 × 1020 ions/cm3 dopant concentration. The diffusion coefficient, D derived from the Y-T model and the energy migration rate, W m attained from the B model has demonstrated diffusion-based energy migration initially at about >1.47 × 1020 ions/cm3 Nd3+ concentration and after that, it has switched to a hopping mechanism with further increasing ion concentration, >2.97 × 1020 ions/cm3. Critical quenching concentration, Q and critical radius, R 0 for the studied glass composition have also been determined and correlated to the experimental results. No evidence for ion clustering has been found within the studied dopant ion concentration range (0.10 × 1020 - 8.15 × 1020) ions/cm3 with respect to the estimated R 0. Finally, the contribution of the individual relaxation process to the experimentally recorded emission spectra and measured lifetime, τ exp has been investigated in order to identify the most suitable Nd3+ ion concentration for developing large-aperture high-energy/high-peak-power lasers and optical amplifiers. Therefore, the present work is expected to be significant in aiding to formulate an effective glass composition for construction of compact high-power lasers and optical amplifiers. [Display omitted] • Analysis of the non-radiative decay processes in Nd3+ doped phosphate laser glass. • At concentrations N Nd 3+ ≤ 0.78 × 1020 ions/cm3, OH-quenching dominates the decay processes. • Energy migration-assisted cross-relaxation mechanisms are demonstrated for Nd3+ self-quenching. • The hopping mechanism dominates energy migration processes at concentrations N Nd 3+ ≥ 1.47 × 1020. • For the concentration range of (0.10─8.15)1020 ions/cm3, there is no evidence of ion clustering. [ABSTRACT FROM AUTHOR]

Here, Cr 3+ sensitized intense luminescence is obtained from Yb 3+ ions in a series of newly formulated Cr-Yb doped Ba-Al metaphosphate glass. It has been observed from measured FTIR and absorption spectra that, Yb 3+ ion plays the role of network modifier by polymerizing the network in this host. The Yb 3+ emission intensity enhanced significantly under Cr 3+ excitation in codoped sample due to Cr 3+ to Yb 3+ energy transfer which is further increased as a function of Yb 3+ concentration up to 1 mol% beyond which decrease of luminescence is observed. The energy transfer from Cr 3+ to Yb 3+ is further improved on inclusion of Nd 3+ ions resulting in slight increase of Yb 3+ emission intensity. This indicates the role of Nd 3+ ions in bridging the energy gap between Cr 3+ and Yb 3+ is nominal due to significant red shift of Cr 3+ emission in this host to bring about effective spectral downshifting which may prove to be useful for production of flash-lamp pumped Yb 3+ lasers as well as solar concentrator applications. [ABSTRACT FROM AUTHOR]

In the present study, we report the formation of transparent glass-ceramics containing BaGdF 5 nanocrystals under optimum ceramization of SiO 2 –BaF 2 –K 2 O–Sb 2 O 3 –GdF 3 –Eu 2 O 3 based oxyfluoride glass and the energy transfer mechanisms in Eu 2+ → Eu 3+ and Gd 3+ → Eu 3+ has been interpreted through luminescence study. The modification of local environment surrounding dopant ion in glass and glass ceramics has been studied using Eu 3+ ion as spectral probe. The optimum ceramization temperature was determined from the differential scanning calorimetry (DSC) thermogram which revealed that the glass transition temperature ( T g ), the crystallization onset temperature ( T x ), and crystallization peak temperature ( T p ) are 563 °C, 607 °C and 641 °C, respectively. X-ray diffraction pattern of the glass-ceramics sample displayed the presence of cubic BaGdF 5 phase (JCPDS code: 24-0098). Transmission electron microscopy image of the glass-ceramics samples revealed homogeneous distribution of spherical fluoride nanocrystals ranging 5–15 nm in size. The emission transitions from the higher excited sates ( 5 D J , J = 1, 2, and 3) as well as lowered asymmetry ratio of the 5 D 0 → 7 F 2 transition (forced electric dipole transition) to that of the 5 D 0 → 7 F 1 transition (magnetic dipole) of Eu 3+ in the glass-ceramics when compared to glass sample demonstrated the incorporation of dopant Eu 3+ ions into the cubic BaGdF 5 nanocrystals with higher local symmetry with enhanced ionic nature. The presence of absorption bands of Eu 2+ ions and Gd 3+ ions present in the glass matrix or fluoride nanocrystals in the excitation spectra of Eu 3+ by monitoring emission at 614 nm indicated energy transfer from (Eu 2+ → Eu 3+ ) and (Gd 3+ → Eu 3+ ) in both glass and glass-ceramics samples. [ABSTRACT FROM AUTHOR]

Abstract: Photoluminescence properties of Bi3+ co-doped Eu3+ containing zinc borate glasses have been investigated and the results are reported here. Bright red emission due to a dominant electric dipole transition 5D0→7F2 of the Eu3+ ions has been observed from these glasses. The nature of Stark components from the measured fluorescence transitions of Eu3+ ions reveal that the rare earth ions could take the lattice sites of Cs or lower point symmetry in the zinc borate glass hosts. The significant enhancement of Eu3+ emission intensity by 346nm excitation (1S0→3P1 of Bi3+ ions) elucidates the sensitization effect of co-dopant. The energy transfer mechanism between sensitizer (Bi3+) and activator (Eu3+) ions has been explained. [Copyright &y& Elsevier]