Inokuti-Hirayama Research Articles

Optical properties of Sm3+ions doped 10SrO-(10−x)Al2O3-10BaCl2-60B2O3-10TeO2 glasses for reddish orange laser applications

In the present work, oxy chloro boro tellurite (OCBT) glasses were prepared with the composition 10SrO-(10−x)Al2O3-10BaCl2-60B2O3-10TeO2-rSm2O (where r = 0.5, 1.0, 1.5, 2.0 and 2.5 mol%) using melt quenching technique. Several optical properties were studied after thorough analysis of absorption, excitation, photoluminescence (PL) and PL decay profiles of these glasses. Judd-Ofelt parameters evaluated from the absorption spectra are used to understand the asymmetry around the Sm3+ ions in the present reported glasses. An effort has been made to understand the PL properties of these glasses by evaluating the key parameters such as branching ratios and stimulated emission cross-sections and quantum efficiencies. In the process of understanding mutual interaction between the Sm3+ ions, Inokuti-Hirayama (I-H) method is applied. CIE color co-ordinates also measured to confirm the reddish orange emission from these glasses. From all obtained parameters, it can be suggested that OCBTSm1.0 glass is aptly suitable for reddish orange laser applications.

Investigations on the luminescence and gamma ray shielding features of Pr3+: BLCZFB glass for orange-red laser and radiation applications

Praseodymium (Pr3+) ions doped barium lithium calcium zinc fluoroborate (BLCZFB) glasses were prepared with the melt quenching technique, and their physical, optical, and shielding properties were estimated. Their amorphous nature was verified with X-ray diffraction (XRD) pattern. Each of their absorption spectra exhibited nine peaks in the visible and near infra-red (NIR) regions. The absorption bands of oscillator strength and Judd-Ofelt (J-O) parameters were used to evaluate their radiative parameters. Their predominant emission peak in their visible emission spectra was observed at 604 nm (16556 cm−1), attributed to 1D2→3H4 transition. And their main emission peak in the NIR emission spectra was at the wavelength of 1458 nm (6858 cm−1), corresponding to the 1D2→1G4 transition. Their spectroscopic properties, including the stimulated emission cross-section (σPE), branching ratio (βR), quantum efficiency (η), gain bandwidth (σPE×Δλeff), and optical gain parameter (σPE×τexp) were also calculated for the visible (1D2→3H4) and NIR (1D2→1G4) emission transitions. From their emission spectra, the color chromaticity coordinates, (x, y) and (u, v), the color purity (CP), and the correlated color temperature (CCT) were calculated. The concentration quenching mechanism and energy transfer process were also explored from the emission spectra. Both the visible and the NIR lifetime curves exhibited non-exponential behaviour for all the glasses. The experimental lifetime decreases with the increase of Pr3+ ions concentration, which could be attributed to the cross-relaxation channels. The decay profiles are well fitted with Inokuti-Hirayama (IH) model (S = 6) to realize the energy transfer process. The energy transfer parameter (Q), donor-acceptor interaction parameter (CDA), and critical distance (R0) were also calculated. Next, the direct and indirect allowed transitions, the band tailing (B), and Urbach parameters (ΔE) were calculated. Then the shielding parameters, including the mass attenuation coefficient (MAC), the mean free path (MFP), and the equivalent atomic number (Zeq), etc., were articulated. Based on the above parameters, 1PrBLCZFB and 2PrBLCZFB glasses are suggested to be used for future solid-state orange-red laser, photonic devices, optical amplifier, and gamma ray shielding.

Judd-Ofelt analysis and visible luminescence of Sm3+: MCZBP glass for reddish-orange laser and multi-colour display applications

A new series of Sm3+ ions doped magnesium cadmium zinc borophosphate (Sm3+: MCZBP) glasses were prepared with melt quenching, and were characterized with X-ray diffraction, optical absorption spectra, excitation spectrum, emission spectra, and fluorescence decay curves. The increase of Sm3+ ions concentration increased the density (ρ), refractive index (n) and decreased the molar volume (Vm) of the glass. The non-metallic nature was identified from the metallization factor (M). The optical absorption spectra were used to understand the optical band gap (direct and indirect). The oscillator strength and Judd-Ofelt (JO) intensity parameters were determined from the optical absorption spectra and further used to evaluate the radiative properties of the Sm3+ ions doped glasses. The luminescence spectra showed the four emissions from transitions 4G5/2→6HJ (J = 5/2, 7/2, 9/2, and 11/2), corresponding to 562 nm (17793 cm−1), 597 nm (16750 cm−1), 644 nm (15527 cm−1) and 704 nm (14204 cm−1) upon exciting with 401 nm (24937 cm−1) wavelength, respectively. CIE chromaticity co-ordinates (x, y), the colour purity (CP), and the correlated colour temperature (CCT) values were calculated, showing that the emission colour fell in the reddish-orange region. The experimental lifetime (τexp), quantum efficiency (η), stimulated emission cross-section (σPE), gain bandwidth (σPE×Δλeff), and optical gain parameter (σPE×τexp) were articulated from the emission spectra of the glasses. The decay curves of 4G5/2 excited state exhibited non-exponential profile for all the present glasses. The efficient energy transfer between two Sm3+ ions through cross-relaxation was analysed with Inokuti-Hirayama (IH) model (S = 6). All the absorption and spectroscopic results revealed that 1SmMCZBP glass had a strong reddish-orange emission at 597 nm corresponding to 4G5/2 → 6H7/2 transition, and could be very promising material for laser and multi-colour display.

Down-conversion luminescence and shielding parameters of Dy3+: NFBT glass for white LED and radiation applications

A new kind of dysprosium (Dy3+) ions doped niobium fluoro borotellurite (NFBT) glass with compositions (35- x )TeO2 + 30H3 BO3 + 15Nb2O5 + 10SrCO3 + 10CdF2 + x Dy 2O3 (where x = 0.05, 0.3, 0.5, 1, 2 and 3 in wt. %, hereafter refers as to Dy 3+ ions’ concentration) was fabricated with melt quenching method and characterized through X-ray diffraction, physical (density (ρ), molar volume of oxygen (V o), and optical basicity ( th), etc.), visible absorption, excitation, emission and lifetime measurements. Its density increases while its molar volume decreases with increase of Dy3+ ions, which indicates that the glass becomes more compact. The absorption spectrum shows the various characteristic peaks of Dy3+ ions attributed to the transitions from the 6H 15/2 ground level to the different excited energy levels. The oscillator strengths and Judd-Ofelt intensity parameters (W l =2, 4 & 6) were articulated from the optical absorption spectrum. The photoluminescence spectrum reveals that this NFBT glass has several emission bands, corresponding to 4F 9/2 → 6H 15/2 (blue), 4F 9/2 → 6H 13/2 (yellow) and 4F 9/2 → 6H 11/2 (red) transitions, respectively. The emission intensity increased with Dy3+ ions concentration from 0.05 wt. % to 1 wt. %, after that the concentration quenching was observed for higher concentrations (2 & 3 wt. %). The non-exponential decay curves were analysed with Inokuti-Hirayama (IH) model ( S =6), indicating a nature of dipoledipole interaction between the donor and the acceptor of Dy3+ ions. The Commission International de’Eclairage (CIE 1931 (x , y) and CIE 1976 ( u , v )) coordinates and the correlated color temperature (CCT) values clearly show that the present glass can be useful in cool white light (CCT>4000 K) region. Moreover, mass attenuation coefficient (μ / ρ), and effective atomic number (Z eff) parameters were also articulated through Phy-X/PSD program. Hence, the results indicate that the prepared glasses could be suitable for laser, smart white LED (1DyNFBT) and gamma ray shielding (3DyNFBT) applications. • A novel series of Dy 3+ : NFBT glasses were prepared with melt quenching. • Luminescence and colorimetric parameters (CIE, CP , CCT, Y/B ratio) were evaluated. • Gamma radiation shielding parameters (MAC, HVL, MFP, Ʃ R , Z eff , etc.) were analysed. • 1DyNFBT and 3DyNFBT glasses can be suggested for WLED and gamma ray shielding applications.

Gd3+/Sm3+energy transfer behavior and spectroscopic study of lithium gadolinium magnesium borate for solid state lighting material

We report the luminescence and energy transfer features in (B2O3)0.55-x(Li2O)0.30 (MgO)0.10(Gd2O3)0.05 (Sm2O3)x glasses, prepared via melt-quenching rout. By employing the Judd–Ofelt (JO) theory, the spectral parameters such as oscillator strengths, stimulated emission cross-sections, radiative transition probability and branching ratios are evaluated from the absorption and emission spectra. The dipole-dipole interaction as a dominant interaction mechanism is confirmed from Inokuti–Hirayama (IH) model. The luminescent color falls in the orange part of commission International de I'Eclaiage (CIE). The ultra-violet (UV) sensitization of visible emission of Sm3+ is analyzed by the photoluminescence (PL) emission spectra and the lifetime measurement. The Gd: 6P7/2–8S7/2 emission in UV range and the Sm3+:4G5/2 –6HJ luminescence at 598 nm were observed upon the excitation of Gd:4f level by λexc = 275 nm. Moreover, the impact of energy transfer on the donor-acceptor luminescence, quantum efficiency, and donor luminescence decay kinetics are investigated. It is found that efficient orange luminescence originates from Sm3+ emitting centers. These findings show that these as-prepared luminescent glasses are promising in orange LEDs and laser applications.

The Physical, Optical, Photo and Radioluminescence Studies of Dy3+ Doped Zinc Barium Gadolinium Phosphate Glasses

The Dy2O3 doped phosphate glasses of chemical composition 10ZnO · 10BaO · 10Gd2O3 · 70P2O5, 10ZnO · 10BaO · 10Gd2O3 · 69P2O5 · 1Dy2O3 and 10ZnO · 10BaO · 10GdF3 · 69P2O5 · 1Dy2O3 were prepared by melt quench technique. The prepared glass samples were characterized through physical and luminescence properties such as density, molar volume, refractive index, FTIR, UV-Vis-NIR absorption spectra, photoluminescence excitation and emissions, radio-luminescence and life time. The J–O theory were analyzed to calculate the radiative properties such as radiative transition probabilities (AR), stimulated emission cross section (σR) and branching ratio (βR). Total nine characteristics absorption peaks belong to Dy3+ ion at the 347, 386, 454, 750, 800, 896, 1089 and1674 nm respectively corresponding to transition from ground state 6H15/2 to excited state 4M15/2+4I15/2, 4F7/2+4I13/2, 4I15/2, 6F3/2, 6F5/2, 6F7/2, 6F9/2 and 6H11/2 are observed in absorption spectra in the 300–1900 nm region. The photoluminescence and radio-luminescence emission spectra of the present glasses were recorded and found in good agreement with one another. The CIE 1931 chromaticity color coordinates were evaluated and it is found that these coordinates positioned in the white region with (x, y) = (0.39, 0.44) values for both oxide and oxyfluoride glasses. The florescence decay time from 4F9/2 level was measured by monitoring the intense 4F9/2 → 6H13/2 (573 nm) transition. The decay time is found to be non-exponential so the non-exponential curve was well fitted to Inokuti–Hirayama (IH) model for S = 6. The results obtained in present work demonstrate that the present glasses could be a good choice for use in white light solid state lighting applications.

Color tunable luminescence and optical temperature sensing performance in a single-phased KBaGd(WO4)3:Dy3+, Eu3+ phosphor

Abstract Herein, a series of Dy3+, Eu3+ single/co-doped KBaGd(WO4)3 phosphors (KBGW:Dy3+, Eu3+ for short) were prepared by solid-state reaction method and investigated by means of X-ray diffraction, SEM, photoluminescence excitation and emission spectra, decay curves and thermal quenching behavior. The KBGW:xDy3+ phosphors exhibited a weak blue emission around 480 nm and a strong yellow emission around 580 nm, corresponding to the characteristic 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions of Dy3+ ions respectively. The decay curves of the KBGW:xDy3+ phosphors were analyzed in the framework of the Inokuti-Hirayama (IH) model and the concentration quenching mechanisms were determined to be dipole-dipole interactions. Under the excitation of 250 nm and 352 nm, both the characteristic emissions of Eu3+ and Dy3+ ions were observed in the KBGW:Dy3+, Eu3+ phosphors. Furthermore, with the increasing concentration of Eu3+, color-tunable emissions from yellow to red were obtained in these samples. Based on the thermal quenching behavior, the optical sensitivity of the sample to temperatures, including absolute sensitivity (Sa) and relative sensitivity (Sr), were calculated and evaluated for the application in optical thermometry.

Spectroscopic study and energy transfer behavior of Gd3+ to Dy3+ for Li2O–MgO-Gd2O3–B2O3–Dy2O3 glasses for white emission material

The present study reports the Gd3+-sensitized Dy3+ luminescence and energy-transfer phenomenon, occurring in (B2O3)0.55-x (Li2O) 0.30(MgO)0.10(Gd2O3)0.05 (Dy2O3)x glasses, quenched by high-temperature melting. We study the Judd-Ofelt (JO) intensity parameters and radiative properties, determined by the absorption and emission spectra. The photoluminescence excitation of the Dy3+ at λem = 575 nm shows the existence of Gd3+ peaks (275 nm and 312 nm) while the emission spectra of the glasses reveal that among the four observed Dy3+ characteristics emissions (482 nm, 575 nm, 663 nm and 753 nm), only the λem = 575 nm enhances due to the excitation of the 4f7 state of the Gd3+ at λexc = 275 nm, an indicative of the effective energy transfer (ET) from the Gd3+ to the 4f-4f electric-dipole transition of the Dy3+. The ET predicts the sensitizer's luminescence decay and activator's luminescence growth, given the fact that an efficient yellow luminescence originates from the activtor's emitting centers. We determine the key parameters such as energy transfer efficiencies, transfer probabilities and average donor–acceptor distance by measuring the lifetimes from the sensitizer Gd3+ ions (λexc = 275 nm and λem = 312 nm) and the activator Dy3+ ions (λexc = 388 nm and λem = 575 nm). In addition, by using the Inokuti –Hirayama (IH) model, we find that the nature of the mechanism of the energy transfer between the Gd3+ and Dy3+ ions is predominantly the non-radiative phonon-assisted electric dipole–dipole. Lifetime of the samples decreases with increasing Dy3+ content (λexc = 388 nm and λem = 575 nm) which shows the resonance energy transfer (RET) within the Dy3+. This proposes that the luminescence and the energy transfer between the Gd3+ and the Dy3+ can be boosted up in the host glass, crucial for the persistent luminescence and spectral conversion/modification. The CIE color coordinates and CCT suggest that the present glasses are useful for white-light emission.

Development of ZnO–BaO–B2O3–TeO2 glass doped with Sm3+ for orange emitting material

Zinc barium borotellurite glass samples were synthesized with the chemical composition of 10ZnO–30BaO–30B2O3-(30-x)TeO2-xSm2O3 (where 0.05 ≤ x ≤ 1.50 in mol%). Several techniques for XRD, FTIR, absorption, luminescence and decay time measurements were used to investigate the structural and spectroscopic properties. It was found that the XRD patterns revealed amorphous nature of the glass samples. The structural modification of (TeO4) trigonal bipyramid structural units was observed using FTIR spectroscopy. The UV–VIS–NIR absorption spectra displayed seven absorption peaks corresponding to the energy transitions from the ground level 6H5/2 to 6F11/2 (947 nm), 6F9/2 (1085 nm), 6F7/2(1238 nm), 6F5/2 (1385 nm), 6F3/2 (1492 nm), 6H15/2 (1550 nm), and 6F1/2 (1589 nm) excited levels of Sm3+ ion. For the emission spectra, four peaks revealed the transitions 4G5/2 → 6H5/2 (563 nm), 6H7/2 (601 nm), 6H9/2 (644 nm) and 6H11/2 (705 nm). The phenomenological intensity parameters Ωλ (λ = 2, 4, 6) according to Judd–Ofelt theory were calculated. The J-O parameters have been used to forecast several radiative properties such as transition probability (AR), branching ratio (βR) and stimulated emission-cross-sections (σp) in 4G5/2 excitation level of samarium ion. The decay patterns of the 4G5/2 level were fitted using non exponential as well as Inokuti–Hirayama (IH) model. The luminescence spectra of Sm3+ ion of the glasses was analyzed with The CIE chromaticity color coordinates. According to the CIE coordinates, it was located in the boundary of orange light in the CIE diagram. All of the results indicated that these glass compositions could be used for preparing a material which will be a potential candidate for laser applications.

NIR luminescence and energy transfer kinetics in Nd3+/Yb3+ co-doped sodium aluminium bismuth fluoro-borosilicate glasses

Here, we demonstrate the results pertaining to energy transfer kinetics in Nd3+/Yb3+ ions combinedly doped in oxy-fluoride based sodium aluminum bismuth fluoro-borosilicate glasses. The thermal stability for the parent NABFBS glass is evaluated from TG-DTA measurement, and Raman & FT-IR spectral profiles were investigated to realize the influence of phonon energy of host NABFBS glass and OH− content on luminescence features of Nd3+ and Yb3+ ions. Upon pumping at 808 nm, Nd3+ glasses displayed intense NIR emission for 1 mol% concentration at 903, 1068 and 1348 nm labeled to corresponding transitions 4F3/2→4I9/2, 4F3/2→4I11/2 and 4F3/2→4I13/2. Effect of multiphonon-, cross-relaxation and OH− group on Nd3+ emission causing luminescence quenching above 1.0 mol % Nd3+ is interpreted. The sensitizing effect of Nd3+ emission on Yb3+ luminescence is investigated by co-doping Nd3+ ion (optimized to 1 mol%) with different Yb3+ ion concentrations. The probability of energy-transfer (ET) between these ions has been substantiated by the considerable spectral overlap of Yb3+ absorption and Nd3+ emission, luminescence features, emission decay rates and energy level diagram. On co-doping Yb3+ to Nd3+, the emission intensity of Yb3+is enhanced along with simultaneous decrement in Nd3+ emission owing to transfer of Nd3+ excitation energy. This process is further supported by the shortening of Nd3+ life-times in co-doped glasses compared with individually Nd3+ doped glasses. The probability of transfer of energy in Nd3+ and Yb3+ combinedly doped system is estimated along the same lines of Dexter's theory and Inokuti-Hirayama (I-H) fitting model for dipole-dipole coupling. The results reveal that, the energy-transfer mechanism from Nd3+(4F3/2)→Yb3+(4F5/2) is a non-radiative type governed by electric dipole-dipole interaction with phonon assistance. The energy transfer parameters, donor-acceptor coupling constant (CDA), energy-transfer efficiency (η) and probability of energy transfer (P) for co-doped glasses are computed from lifetime curves. In addition, back energy transfer Nd3+←Yb3+ is also investigated.

Physical, optical and luminescence properties of the Dy3+doped barium borophosphate glasses

Barium borophosphate glasses doped with dysprosium oxide had been fabricated by conventional melt quenching technique using the chemical composition of: (25BaO: 5B2O3: 70-xP2O5: xDy2O3)), where (x = 0.2, 0.4, 0.6, 0.8 and 1.0, mol%) (BaBPDy). The physical, optical and luminescence properties are studied for possibility of using as a white luminescence materials for solid-state light emitting devices. Judd-Ofelt (JO) theory is applied to study the radiative properties of the luminescence level of Dy3+ ions. The effect of the concentration quenching due to increase in Dy3+ ions is discussed in details. The lifetime of all BaBPDy concentration glass is bi-exponential in nature, which is discussed in the present work. This non-exponential nature of the decay curve was fitted by using the well-known Inokuti-Hirayama (IH) model S= 6, indicating that the energy transfer process is dipole-dipole type. The chromaticity co-ordinate(x, y) is evaluated from the luminescence spectra and its possibility for using as a white light application has been analyzed.

Studies on structural characterization and near white light emission through energy transfer between Ce3+ and Tb3+ in barium gallium borosilicate glasses

Glasses of the composition 30BaO‒2Ga2O3‒ (27.8‒x) B2O3‒40SiO2‒xCe2O3‒0.2Tb2O3 (0 ≤ x ≤ 1.0) were synthesized by conventional melting and quenching process. The samples were characterized by XRD, EDS, TG-DTA, FT-IR and Raman studies. Optical absorption (OA) and photoluminescence (PL) spectral studies were performed. X-ray diffraction patterns of samples have clearly confirmed the amorphous nature of the samples. Differential thermal analysis indicated thermal stability of glasses. Raman and FTIR spectra have exhibited different fundamental vibrational bands of borate and silicate structural units. The absorption spectra exhibited four absorption bands of Tb3+ ions from the ground state 7F6 in the visible and NIR regions. In addition, a feeble band corresponding to 4f (2FJ) → 5d (2A1g) absorption transition of Ce3+ ions at 416 nm is also located in these spectra. Optical bandgap (Eg) evaluated using Tauc plots, is observed to decrease with increase of Ce2O3 up to 0.6 mol%. Luminescence spectra (recorded at λexc = 329 nm) of glass co-doped with 0.6 mol% CTb exhibited the maximal PL output. The non-exponential time decay profiles are finely fitted to Inokuti-Hirayama (I-H) model for S = 6. This observation suggests that the energy transfer mechanism between Ce3+ → Tb3+ is connected with the dipole-dipole interaction. The CIE coordinates of 0.6CTb glass are estimated to be (0.257, 0.307). These values are found to be nearer to the standard values of ideal white light and hence it is concluded that the glass of this composition is useful for white LEDs.

Color tunability and energy transfer studies of Dy3+/ Eu3+ co-doped calcium aluminozincate phosphor for lighting applications

Dy3+ doped and Dy3+/Eu3+ co-doped calcium aluminozincate (CAZ) phosphor synthesized by Pechini sol-gel method. Structural and morphological analysis were carried out by using X-ray diffractometer (XRD) and field emission scanning electron microscope (FE-SEM). The photoluminescent (PL) spectra were recorded and energy transfer mechanism between Dy3+ and Eu3+ ions were studied using Dexter and Reisfeld’s approximation. The colorimetric properties were studied by evaluating CIE coordinates and correlated color temperature (CCT). The energy transfer mechanism was analysed by applying Inokuti-Hirayama (I-H) model on decay curves as well. The thermoluminescence (TL) glow curve analysis reveals two trap centres in the present host. The obtained results indicate that the CCT can be tuned from warm to cool region and color tunability can also be achieved in Dy3+/Eu3+ co-activated CAZ phosphor by varying the excitation wavelength or activator concentration in the host lattice and hence can be effectively utilized in white light emitting diodes (wLEDs).

Sol-gel synthesis and luminescent properties of a novel KBaY(MoO4)3:Dy3+ phosphor for white light emission

Abstract A novel kind of yellow KBaY(MoO4)3:Dy3+ (KBYM:Dy3+ for short) phosphor was prepared via sol-gel method and evaluated as a component candidate for NUV excited LED. The structure, morphology and luminescent properties of the as-synthesized phosphor were investigated by means of X-ray diffraction (XRD), Raman spectra, scanning electron microscope (SEM), excitation and emission spectra, and decay curves. The results of XRD and Raman spectra show that KBYM:Dy3+ phosphors can be synthesized by sol-gel method at a minimum temperature of 550 °C. The excitation spectra exhibited intense absorption bands in the NUV and blue region, which match well with the commercial LED chips. Under the excitation of 352 nm, a dominant emission was found at 575 nm corresponding to the 4F9/2 → 6H13/2 transition, which means that Dy3+ ions occupy a low symmetry site in KBYM matrix. The thermal stability of the phosphor was investigated based on the crossover model, and the activation energy was determined to be 0.235 eV. The Inokuti-Hirayama (IH) model has been applied to the analysis of the decay curves, and the results showed that the energy transfer process among Dy3+ ions is controlled by dipole-dipole interactions. Lastly, both yellow and white LEDs were fabricated with the as-synthesized phosphor and their luminescent performances were investigated as a function of filament currents.

Tunable white light by varying excitations in yttrium alumino bismuth borosilicate glasses co-doped with Dy3+-Eu3+ for cool WLED applications

Yttrium alumino bismuth borosilicate (YABiBS) glasses doped with RE3+ ions (Eu3+, Dy3+, Dy3+- Eu3+) have been synthesized via standard melt quenching technique and their emission properties were investigated. Optical analysis of these glasses is characterized by absorption and luminescence. XRD spectra reveal that these glasses have amorphous nature. The absorption spectra of these co-doped glasses consist five bands of Dy3+ which are assigned to 6H15/2 → 6F3/2 (750 nm), 6F5/2 (796 nm), 6F9/2 (1085 nm), 6F11/2 (1264 nm),6H11/2 (1677 nm) and another four bands of Eu3+ assigned to 7F0 → 5L6 (393 nm) Meza-Rocha et al. (2017) [5],5D2 (464 nm), 7F6 (2097 nm), and 7F1 → 7F6 (2202 nm). It is also witnessed a broad band having electronic transition 1S0 → 1P1 is due to Bi3+ ions. Optical band gaps, nephelauxetic ratio, and bonding parameters are discussed by using optical absorption data. Eu3+ single doped glasses show five emission bands, with the n-UV excitation wavelength 393 nm, in which characteristic feature red emission (612 nm) is recognized with transition (Meza-Rocha et al., 2017 [5])D0 → 7F2. At the same time, Dy3+ single doped glasses illuminated with the excitation wavelength of 385 nm shows their known natural emissions blue (481 nm) and yellow (574 nm), having transitions 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 respectively. Emission for co-doped glasses Dy3+-Eu3+ are excited with the different selected ultraviolet wavelengths such as 464 nm, 392 nm, 385 nm, 363 nm, and 348 nm. It can be observed that tunable emission from both the ions (Dy3+, Eu3+) from orange reddish emission to white emission. The energy transfer from Dy3+ to Eu3+ is manifested by the quadrupole-quadrupole mechanism, which is confirmed by Inokuti-Hirayama (IH) modal based on lifetime decay curves. Also, the efficiencies and probabilities of energy transfer are determined based on the results of decay curves. The CIE color coordinates of DE1.0 glass with the excitation 348 nm gives x, y coordinates as (0.332, 0.342) which confers the good white emission. CCT value for this glass is around 5520 K shows that useful for cool WLED applications.

Investigation of site occupancy and photoluminescence of Ce3+ in cubic borate Ba3Y2(B2O5)3 and Ce3+ → Tb3+ energy transfer behavior

Ce3+, Tb3+ and Ce3+-Tb3+ activated Ba3Y2(B2O5)3 phosphors were synthesized by a sol-gel pyrolysis method. The synthesized phosphors were investigated using X-ray diffraction (XRD) analysis, photoluminescence emission and excitation spectra and luminescence decay curves. In the Ce3+ activated Ba3Y2(B2O5)3 samples, two different Ce3+ centers (marked as Ce(1) and Ce(2)) could exist. The Ba3Y2(B2O5)3:Tb3+ phosphor shows some emission peaks at ∼350–650 nm among which the green emission peak at 540 nm is the strongest. For the Ba3Y2(B2O5)3:Ce3+, Tb3+ co-doped phosphor, the existence of energy transfer process from Ce3+ center to Tb3+ center is confirmed and the interaction mechanism between Ce3+ and Tb3+ in Ba3Y2(B2O5)3:Ce3+,Tb3+ system is dipole-dipole interaction based on Inokuti–Hirayama (IH) model.

Influence of modifier oxides on spectroscopic properties of Eu3+ doped oxy-fluoro tellurophosphate glasses for visible photonic applications

Oxy-fluoro tellurophosphate glasses with molar composition (40-x)P2O5-20TeO2-20ZnF2-20RO-xEu2O3 (where R = Ca, Sr, and Ba and x = 1) were prepared by melt quenching technique. The structural, optical, and photoluminescent properties were studied for the prepared glass. The Fourier transform infrared (FT-IR) studies revealed the presence of poly-phosphate structure and maximum depolymerization was observed for BaO network modifier mixed glass. The band gap and Urbach energy values were calculated based on the absorption spectra. The intense emission peak was observed at 613 nm (5D0→7F2) under the excitation of 392 nm, which matches well with the emission of commercial near ultraviolet (n-UV) LED chips. The highest emission intensity and quantum efficiency were observed for BaO network modifier mixed glass. Based on these results, BaO network modifier glass samples with molar composition (40-x)P2O5-20TeO2-20ZnF2-20BaO-xEu2O3 (x = 3, 5, 7, and 9) were prepared to optimize the emission intensity. The optimized doping concentration of Eu2O3 was 5 mol% and the Commission International de l’Eclairage (CIE) chromaticity coordinates fall in the red region. The interaction among Eu3+ ions was dipole-dipole in nature, which was confirmed by Dexter theory and Inokuti-Hirayama (I-H) model. The above results suggest the applicability of the glass as a potential red photoluminescent material in photonic devices.

Spectroscopic studies of Dy3+ ions doped barium lead alumino fluoro borate glasses

Barium lead alumino fluoro borate (BaPbAlFB) glasses doped with Dy3+ ions were prepared by using melt quenching technique and characterized using various spectroscopic techniques to understand their usage in photonic devices. The SEM and EDX spectral studies were performed on the as prepared glasses to understand the glassy nature and elemental analysis respectively. The weight loss in the BaPbAlFB glass has been studied by the TGA. Judd-Ofelt (J-O) theory has been applied to the measured oscillator strengths of the absorption spectral features to evaluate radiative parameters for the prominent emission transitions of Dy3+ ions in BaPbAlFB glasses. The photoluminescence (PL) spectral measurements show concentration quenching beyond 1.0 mol% of Dy3+ ions in the as prepared glasses. The decay profiles observed for higher concentration of Dy3+ ions in these glasses are well fitted to Inokuti-Hirayama (IH) model to understand the energy transfer mechanism involved in the as prepared glasses. The experimental lifetimes (τexp) measured from the decay spectral features are correlated with radiative lifetime (τR) values to understand the quantum efficiency (η) of the as prepared glasses. From the PL spectra, colorimetric parameters such as CIE coordinates, correlated color temperature (CCT) and yellow-to-blue (Y/B) intensity ratios have been estimated to understand the usage of these glasses in photonic devices such as white LEDs and lasers.

Energy transfer (Ce3+→ Sm3+) influence on PL emission of Ce3+/Sm3+ co-doped barium gallium borosilicate glasses

30BaO2Ga2O3‒(27.8−x)B2O340SiO2xCe2O30.2Sm2O3(0 ≤ x ≤ 1) glasses were synthesized by conventional melting and quenching processes. The characterization of samples was performed using XRD, EDS, FTIR and Raman studies. Later, Optical absorption (OA) and photoluminescence (PL) spectral were recorded. X-ray diffraction pattern indicated amorphous nature of the samples. Raman and FTIR spectra have confirmed the presence of various, borate and silicate structural groups in the glass matrix. Structural modifications in glass matrix were clearly observed with variation of glass composition and increasing asymmetry led to depolymerisation of the glass structure. The absorption spectra exhibited nine absorption bands of Sm3+ ions in the vis–NIR regions excited from the ground stated 6H5/2. Additionally, a feeble band corresponding to 4f (2FJ) →5d (2A1g) absorption transition of Ce3+ ions (at 415 nm) is also observed in these spectra. Optical band gap (Eo) evaluated using Tauc plots is observed to decrease with Ce3+ concentration. PL emission of Sm3+ ions (recorded at λexc = 350 nm) in the co-doped glasses is observed to increase with increase of Ce2O3 content up to 0.6 mol%. The non-exponential decay curves are well fitted to I-H (Inokuti-Hirayama) model by S = 6, suggesting that the nature of the energy transfer between Ce3+→ Sm3+ in terms of dipole-dipole interaction. The CIE coordinates for 350 nm excitation of emission of 0.6CSm glass was observed to be exist in near white light region; hence these glasses may be considered for white LED's applications.

Photoemission and thermoluminescence characteristics of Dy3+-doped zinc sodium bismuth borate glasses

The present study reports preparation and characterization of Dy3+-doped PbO free alkali-heavy-metal-borate glasses for luminescent applications. The amorphous nature of the glasses and the presence of various structural groups like BiO6, BO3 and BO4 were confirmed through XRD and FTIR measurements. The Oscillator strength of Dy3+ absorption transitions as well as the bond formed with the O2− ion in the glass network were determined using the absorption spectra. Radiative parameters extracted from Judd-Ofelt theory proved the degree of suitability of prepared glasses for lasing applications. The photoluminescence spectra exhibited the emission characteristics of Dy3+ ions and used to calculate the branching ratio, stimulated emission cross-section and radiative lifetime. Metastable lifetimes of Dy3+ ions were obtained through exponential fitting of respective decay profiles. The luminescence quenching phenomena was reasoned using Inokuti-Hirayama (IH) model. The optical gain and quantum efficiency values clearly suggested Dy3+ doping at 0.3 mol% was optimum for 587 nm lasing action. Further, CIE chromaticity plot indicated the possible applications in solid state lighting devices. The thermoluminescence glow curves of 0.3 mol% Dy3+-doped glasses were considered for gamma irradiation and kinetic parameters of the same were evaluated using Computerized Glow Curve Deconvolution (CGCD) technique.