Photoluminescence of terbium doped oxyfluoro-titania-phosphate glasses for green light devices

Terbium (Tb³⁺) doped oxyfluoro-titania-phosphate glasses of chemical composition (in mol%), (60 - x) P₂O₅ – 15 BaF₂ – 20 CaF₂ – 5 TiO₂ – x Tb₄O₇, x?=?0.05, 0.1 and 0.1 were fabricated by usual melt-quenching technique. Photoluminescence (PL) properties of the samples have been investigated by excitation, emission and decay profiles. Upon excitation at 377?nm, the PL spectra exhibit an intense band at 541?nm which corresponds to the ⁵D₄ → ⁷F₅ transition. The intensity ratio of green-to-blue (I_G/I_B) was found to be 9.2 for 0.1?mol% of Tb³⁺-doped glass. High-energy absorption bands were not resolved in the absorption spectrum but disclosed in the photoluminescence excitation spectrum. Decay curves were unveiled non-exponential and mono-exponential behaviours for the ⁵D₃ and ⁵D₄ levels, respectively. Lifetime of the ⁵D₃ and ⁵D₄ levels was decreased up to 0.1?mol%, and thereafter it was increased with the increase of Tb³⁺ ion concentration upon 377?nm excitation. The CIE chromaticity coordinates were supported that the green emission was predominant in Tb³⁺-doped oxyfluoro-titania-phosphate glasses.     

Effect of mixed rare-earth ions on the structural and optical properties of some borate glasses

In order to study some effects of mixed ions of rare-earth (Sm and/or Dy) on the properties of a glass system, the formula 80% B₂O₃+ 18% Na₂O + (2-x)% Sm₂O₃ + (x) % Dy₂O₃; x = 0, 0.4, 1.6 and 2 mol. % has been prepared via the well-known melt quenching method. The presence of some structural groups such as BO₃, BO₄, as well as N₄ factor have been scrutinized via FTIR spectra. Absorbance of the prepared solid glass system has been performed by a spectrophotometer in wavelengths between 190 and 1100 nm. Using traditional techniques and standard formulas, the density (ρ_emp and ρ_exp), bond density (n_B), molar volume (V_m), Fermi energy (E_F), refractive index (n), optical bandgap (E_g) have been determined, then the impact of mixed rare-earth oxides (Dy and/or Sm) on the structural and optical properties have been scrutinized. The density, optical bandgap, IR intensity and the refractive index of glass samples shows nonlinear trend, which can be ascribed to the mixed effect of rare-earth cations. However Sm and Dy have been doped with the same percent in the glass system separated and mixed, the effect of Sm ions is obvious than Dy ions.     

Structure,stability and optical parameters of cobalt zinc borate glasses

In this study, the impact of cobalt oxide (CoO) on the structure, stability, linear and nonlinear optical parameters of B₂O₃–Na₂O–ZnO glasses was scrutinized. A series of glass system (ZnCoNaB-glasses) was successfully prepared through the melt quenching approach. Optical absorbance, reflectance, transmittance and FTIR spectroscopy were performed for all ZnCoNaB-glasses. The FTIR results showed that the BO₄ units are enhanced while nonbridging oxygens are decreased with further CoO addition. Furthermore, ZnO exists as four-coordinated [ZnO₄] units and these units decreased with further doping of CoO. These structural variations produce a decreasing impact in Urbach energy and nonlinear refractive index, meanwhile enhance the glass stability. Further, the metallization criterion (M) values indicate that our glass samples can be used for a new generation of nonlinear optical glasses. The preceding results can predict that the investigated ZnCoNaB-glasses will be utilized in versatile applications; especially optical switching and computing.     

The role played by dopant ions for the production of broadband white light emission from metal oxide nano-powders under laser diode excitation

We report on the role played by dopant ions to create broadband white light emission from metal oxide nano-powders. Y₂O₃ was doped with different rare earth ions (Nd³⁺, Er³⁺, Yb³⁺) and Cr³⁺ ion to investigate their role on the production of white light emission. We have determined that the dopant ions have a facilitator but not a decisive role on the production of the white light emission by doing measurements such as reflectance, white light emission, excitation power dependency and color quality parameters. All measurements showed that the production of white light does not depend on the amount and the type of the dopant ions.     

Spectroscopic characterizations and investigation of Judd-Ofelt intensity parameters of Dy3+-doped Ba2La8(SiO4)6O2 near white light emitting phosphor

A series of Dy³⁺-activated Ba₂La₈(SiO₄)₆O₂ phosphors were synthesized using the solid-state method with the objective of developing single host white light emitting phosphors for use in solid state lighting applications. The Dy³⁺ concentration varied between 0.01 and 0.05 mol%. The as-prepared phosphors crystal structure, optical, and photoluminescent properties (PL), along with energy transfer mechanism and luminescence decay, were investigated. The production of a single-phase Ba₂La₈(SiO₄)₆O₂ with hexagonal symmetry was verified by the findings of the X-ray diffraction analysis. When the Ba₂La₈(SiO₄)₆O₂: Dy³⁺ phosphors are exposed to ultraviolet light, they emit the characteristic yellow PL emissions caused by the ⁴F_9/2 → ⁶H_13/2 transition. The Judd-Ofelt (J-O) parameters (Ω₂, Ω₄, Ω₆) were computed using the excitation spectra. The characteristics of the Dy³⁺ transition indicate that the asymmetric environment around the ligand was suggested by the trend, which was followed by J-O parameters. Due to the dominance of the electric-dipole transition in the luminescence spectrum, the Ba₂La₈(SiO₄)₆O₂:0.03Dy³⁺ phosphor displayed yellowish white emission with CIE coordinates of (0.358, 0.398) and a CCT of 4724 K. The synthesized phosphor may be a useful material in the fabrication of white-emitting phosphor for LEDs application.     

The role of PbO/Bi2O3 insertion on the shielding characteristics of novel borate glasses

Impacts of lead and bismuth oxides insertion on a novel glass system of P₂O₅, B₂O₃, Li₂O, Al₂O₃ according the formula 25B₂O₃–25P₂O₅–10Li₂O–5Al₂O₃–5ZnO-xPbO+ (30-x)Bi₂O₃, x = 5,10, 15, 20, 25 mol%. The mass attenuation coefficient (μ_m = μ/ρ) simulated between 0.015 and 15 MeV using MCNP and calculated theoretically using Phy-X/PSD program. Based on the simulated μ_m, other significant parameters such as linear attenuation coefficient (LAC), half and tenth value layer (HVL, TVL), mean free path (MFP), and effective atomic number (Z_eff) were calculated for fabricated glasses. The G-P fitting methods were used to calculate the exposure and energy absorption buildup factors (EBF and EABF) for fabricated glasses. Furthermore, fast neutron removal cross sections (Σ_R) were calculated theoretically for fabricated glasses. The prepared glasses were effective shielding material which can reduce fast neutrons as well as gamma rays.     

Detailed optical analysis of Dy3+ and Pr3+ co-doped alumino-borate glasses for visible lighting applications

A new glass series with nominal molar composition of 60B₂O₃ + 30NaF + 10Al₂O₃ co-doped with Dy³⁺ and Pr³⁺, synthesized by melt quench was reported. The influence of Rare Earth (RE) ratio variation on prepared glasses was investigated by using Fourier Transform Infra-Red spectroscopy, UV–Vis–NIR absorption spectroscopy, Photoluminescence, Decay curves and Density measurements. Their X-Ray Diffraction and FTIR spectra revealed the glassy nature and confirmed that AlO₆, AlO₄, BO₃ and BO₄ units are the main structural units of that matrix. A non-linear variation following the same trend for tetragonal borate units (N₄), Band gap, non-linear optical properties, Density, Molar Volume etc. was observed. Different optical parameters were obtained by UV–Vis–NIR spectroscopy. The Bonding parameter obtained from Nephelauxetic study indicated ionic nature of Dy³⁺ and covalent nature of Pr³⁺ ions. Photoluminescence excitation and emission spectra were recorded under variety of excitation wavelengths and corresponding color parameters were calculated using 1931 CIE standards. A detailed yellow to blue ratio analysis was reported as a function of RE ion concentration and excitation wavelengths. Composition DPNAB(x = 0.7) displayed the best performance with CIE coordinates (0.33, 0.37). Existence of Energy transfer from Dy³⁺ and Pr³⁺ was evidenced by the spectral overlap diagram and lifetime values obtained from fitting of Decay curves. From the obtained results, prepared glasses can be suggested for solid-state lighting devices like WLEDs and display devices.     

Structural and spectroscopic properties of some neodymium-boro-germanate glasses and glass ceramics embedded with silver nanoparticles

Neodymium-boro-germanate glasses and glass ceramics (with Nd₂O₃ contents up to 40 mol%) embedded with silver metallic nanoparticles (AgNPs) were prepared by the melt-quenching technique. Two series of samples (with AgNPs and without AgNPs) were investigated by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, diffuse reflectance ultraviolet–visible (DR-UV–vis) spectroscopy and photoluminescence (PL) spectroscopy. XRD data reveal that for both series the samples with x < 40 mol% Nd₂O₃ are basically amorphous containing only small amounts of a crystalline phase (identified as crystalline B₂O₃) while for samples x = 40 mol% Nd₂O₃ an important amount of a crystalline phase (identified as the NdBO₃ orthorhombic phase) is present. FT-IR spectroscopy data show that addition of controlled amounts of Nd₂O₃ and AgNPs changes the structural units that build up the host glass ceramic network. These changes were confirmed also by the photoluminescence spectra that show that addition of AgNPs to the host matrix produces changes at the level of emission peaks. The positive values of bonding parameter (δ) calculated based on DR-UV–vis data indicate a covalent character of the bonds from the studied samples.     

Enhancement of luminescence properties and the role of ZnO in Tb3+ ions doped zinc aluminum phosphate glasses

Terbium ion doped zinc aluminum phosphate (ZAP) glasses with composition (90−x)((90−y)P₂O₅–10Al₂O₃–yZnO)–xTb₂O₃ (x=0.5–9 in mol% and y=30, 35, 40 in mol%) have been prepared by melt quenching method, and the effects of the Tb₂O₃ and ZnO content on the luminescence properties have been studied by photoluminescence spectroscopies. It was found that the green emission peaked at 544 nm is significantly enhanced under higher Tb₂O₃ content, meanwhile the sensitization effect of ZnO content is confirmed from the enhanced main emission. The quenching effect attributed to the resonant energy transfer through the cross-relaxation mechanism is observed when Tb₂O₃ concentration is beyond 2.5 mol% due to the fact that more Tb³⁺ ions enhance the 4f→5d and 4f→4f electronic transitions through the dipole–dipole (d–d) interaction. Also, ZnO plays a role of the disperser to prevent non-radiative de-excitation process. A characteristic luminescence image of the (100−x)(60P₂O₅–10Al₂O₃–30ZnO)·xTb₂O₃ series glasses under UV excitation at 366 nm is presented for the first time, and the transition of luminescence suggests that the Tb³⁺-doped ZAP glasses are suitable for green and dual-color blue/green LED applications by modulation of Tb and ZnO composition.     

Energy transfer and luminescence study of Dy3+ doped zinc-aluminoborosilicate glasses for white light emission

A series of Dy³⁺ doped aluminoborosilicate glasses with general formula 20SiO₂-(40-x) B₂O₃–10Al₂O₃–20NaF₂–10ZnO-xDy₂O₃ (x = 0, 0.1, 0.5, 1.0. 1.5, 2.0 and 2.5 mol %) were prepared by melt-quenching method. The FTIR analysis confirms the presence of stretching and bending vibrations of BO₄, BO₃ and SiO₄ units in the prepared glasses. DTA results show that Tg is decreasing with addition of Dy³⁺ ions in the glass system. Theoretically calculated mechanical properties such as elastic modulus, bulk modulus, shear modulus and Poisson's ratio suggest the increase in mechanical stability of glasses with dysprosium addition. Also experimental analysis carried out using Vicker's microhardness suggests glass stability with applied loads. Absorption spectrum shows twelve bands that exist due to transition from ⁶H_15/2 level to different excited levels. Nephelauxetic ratio and bonding parameter calculated shows decreasing ionicity of glasses with increase in Dy³⁺ ions. Judd-Oflet parameter calculated for all the glasses follow the trend Ω₆ > Ω₄ > Ω₄. Luminescence study shows three emission peaks having transitions from ⁴F_9/2 → ⁶H_15/2 (blue), ⁴F_9/2 → ⁶H_13/2 (yellow) and ⁴F_9/2 → ⁶H_11/2 (red). Radiative parameters calculated suggest higher stimulated emission cross-section for present glasses having ⁴F_9/2 → ⁶H_13/2 transition. The decay measurement for all the glass samples were recorded with an excitation at 350 nm and monitoring emission at 575 nm corresponding to the ⁴F_9/2 → ⁶H_13/2 transition and decay curves were fitted to bi-exponential fit. The CIE colour chromaticity coordinates were determined using CIE chromaticity diagram and the values were found to be in close proximity with the standard white light (0.33. 0.33) for all the glasses. Further colour correlated temperature values were found to lie in the near bright white region with CCT around ~4000 K.     

Thermoluminescence features of alumina-mixed borophosphate glasses with Tb3+ ions for dosimetric applications

Amorphous barium borophosphate materials doped with small quantity of terbium ions and with the addition of some amounts of alumina were prepared. Thermoluminescence (TL) characteristics of these glasses were investigated after irradiating them with different doses of γ-rays (in the range 0.5-8.0 kGy). The TL emission exhibited a dosimetric peak at about 210°C. The TL output under this glow peak is observed to increase with the γ-ray dose. For any fixed γ-ray dose, the TL output is increased with increase in Al₂O₃ content up to 3.0 mol%, and beyond this concentration, quenching of TL is visualized. The dose response of TL output of these glasses exhibited linear behavior in the dose range 0.5-4.0 kGy. The mechanisms responsible for TL emission and the variation of TL output with the concentration of Al₂O₃ are quantitatively discussed in terms of structural defects induced during γ-ray irradiation. Finally, it is concluded that these glasses are potential materials for dosimetry applications in the dose range 0.5-4.0 kGy.     

Controlled growth and spectroscopy characterization of blue violet perovskite quantum dots in borate glasses

Blue violet light emitting CsPb(Cl/Br)₃ perovskite quantum dots glasses (QDGs) have been successfully fabricated in multi-component borate glass matrix by melt quenching and heat treatment. The spectral characteristics have been evaluated by photoluminescence (PL), PL excitation (PLE), PL decay and absorption spectra. The recipe and preparation conditions have been optimized for controlled growth of QDs. By using raw materials of NH₄Br/NH₄Cl/PbO and crucible cover, optimizing composition of Na₂O/K₂O in matrix, melting temperature and time, heat treatment temperature and time, and NH₄Cl and NH₄Br contents, we have finally realized blue violet exciton emission in target range of 405–440 nm. The PL wavelength adjustment is comprehensive effect of the abovementioned influence factors. The emission in short wavelength of 405–440 nm is due to controlled growth of the QDs. In final CsPb(Cl/Br)₃ QDs, the contents of Cl and Br are suitable and the Cl/Br ratios are large. A little Br is necessary for growth of CsPb(Cl/Br)₃ QDs and then the Br is partially replaced by Cl at suitable treatment condition. Unsymmetrical PL spectrum profile of some samples is explained as reabsorption effect by monitoring PL spectral profile and PL decay. The temperature characteristics of PL spectra show good recoverability after a temperature cycle.     

Luminescence properties of Sm3+ ions doped heavy metal oxide tellurite-tungstate-antimonate glasses

The trivalent Sm³⁺ ion doped tellurium-antimony-tungsten oxides based glasses were prepared by conventional melt quenching and pressing method. Spectroscopic characterizations such as optical absorption, photoluminescence and decay profile measurements were performed on the glasses. Judd-Ofelt theory is used to evaluate the oscillator strengths and the three phenomenological intensity parameters (Ω_λ, λ = 2, 4, 6) of the glasses. The photoluminescence spectra recorded under 479 nm excitation exhibited the emission bands at 562, 598, 645 and 708 nm corresponding to the transitions ⁴G_5/2 → ⁶H_J (J = 5/2, 7/2, 9/2, 11/2) respectively. Using J-O parameters (Ω_λ) various important radiative parameters viz., transition probabilities, emission cross-sections, branching ratios of various emission bands were evaluated. Decay profiles were recorded to find the lifetime of the ⁴G_5/2 excited level and the obtained life time values are observed to decrease with an increase of Sm³⁺ ion concentration; such decrease is attributed due to clustering of Sm³⁺ ions which may cause luminescence quenching.     

Optical properties of ternary zinc magnesium phosphate glasses

Ternary phosphate glasses of the system (ZnO)₃₀(MgO)_x(P₂O₅)_70−x with x ranging from 5 to 20 mol% were prepared by melt quenching technique. The optical absorption spectra of these glasses were measured at room temperature in the wavelength range between 190 and 1100 nm while the refractive index at wavelength 632.8 nm. The optical absorption indicates that the electronic transition is indirect and associated with phonon-assisted transition. From the absorption spectra, the optical energy band gap (E_opt) and Urbach energy (E_U) values for all the glass samples were calculated from their ultraviolet edges. The values of E_opt is found to increase from 3.36 to 3.44 eV and values of E_U decrease from 0.47 to 0.29 eV with the increase of MgO content. Variation in these optical parameters, density and molar volume is discussed and correlated with the structural changes within the glassy matrix.     

Effect of alkali and alkaline earth metal ion as glass modifiers on the spectroscopic characteristics of Er3+-ion doped lead silicate glasses

The spectroscopic characteristics of Er-doped lead silicate glasses were investigated with respect to the effects of glass modifiers (Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺) with various optical basicities. Using the absorption spectra of the glasses, the Judd–Ofelt parameters of the glasses were calculated and examined, with an emphasis on the glass emission intensity ratio at 1572 nm. The spectra of the samples at low temperatures were examined, and the Stark splitting of Er3+ was investigated. The McCumber method was used to determine the emission cross sections of glasses. The SPM glass exhibited high values of full width at half maximum (51.24 nm) and the emission cross section at 1572 nm (1.908 × 10⁻²¹ cm²), with potential applications for guiding component design of 1.5-μm fiber lasers and amplifiers.     

Linear and nonlinear optical characteristics of CsPbBr3 perovskite quantum dots-doped borosilicate glasses

CsPbBr₃ perovskite QDs are precipitated in a borosilicate glass matrix, while protects efficiently the QD from photo-induced and chemical degradation. We show that the CsPbBr₃ QD doped glasses exhibit strong visible photoluminescence (PL), which is dependence on the concentration that can be controlled by heat treatment conditions. Due to the stabilization by the glass matrix, we are able to determine the nonlinear optical (NLO) properties with a Z-scan technique. We observe a cross-over from saturated absorption (SA) to reverse saturated absorption (RSA) by either increase the pumping intensity or the QD size, reminiscent of quantum size effect in the NLO response. The RSA is associated with two-photon absorption (TPA) that induces strong upconversion luminescence of QD doped glass samples. Our results imply that the glasses containing CsPbBr₃ QDs may find potential applications from solid state lighting to ultrafast optical switches.     

Color-tunable luminescence performance of single-component Na5Y(MoO4)4:Dy3+, Tm3+ white-emitting phosphor for white light-emitting diodes

The single-component Na₅Y(MoO₄)₄:Dy³⁺, Tm³⁺ white-emitting phosphor was prepared by the sol-combustion method, and Tm³⁺ was codoped for color-tunable white emission. The XRD patterns confirm that the as-prepared samples have a Na₅Y(MoO₄)₄ structure and do not change with Dy³⁺/Tm³⁺ codoping. Under ultraviolet excitation at 352 nm, the Na₅Y(MoO₄)₄:Dy³⁺ phosphor shows a characteristic white emission consisting of a weak peak at 485 nm and a strong peak at 577 nm. By codoping a small amount of Tm³⁺, the blue emission of phosphor is enhanced, and the chromaticity coordinates can be adjusted between (0.3663, 0.416) and (0.319, 0.3407); thus, color-tunable white emission is achieved with the synergistic effect of Dy³⁺ and Tm³⁺. The luminescence intensity of Na₅Y(MoO₄)₄:Dy³⁺, Tm³⁺ at 483 K still retains 72% of the initial intensity, showing excellent thermal stability. By combining Na₅Y(MoO₄)₄:Dy³⁺, Tm³⁺ with a 365 nm chip, the fabricated w-LED device emits bright white light for illumination. Therefore, the as-prepared Na₅Y(MoO₄)₄:Dy³⁺, Tm³⁺ has potential applications in the field of w-LEDs as white-emitting phosphors.     

Influence of molybdenum oxide on structural,optical and physical properties of oxychloride glasses for nonlinear optical devices

The unconventional Heavy Metal Oxide Glasses (HMOG) are characterized by a low phonon energy, large infrared range transmission, high refractive index and nonlinear optical properties. Ternary glasses have been synthesized and studied in the Sb₂O₃– MoO₃-ZnCl₂ system. Further, the glass formation compositional limits are reported and some glass samples with the formula: (90-x)Sb₂O₃ -xMoO₃–10 ZnCl₂ (10 ≤ x ≤ 50, mole%) were elaborated. Thermal properties have been measured and indicating that the glass transition temperature decreases with increasing proportions of molybdenum oxide. The evolution of density, microhardness and elastic modulus has been studied as functions of parameter x and Raman spectra measurements have been shown the partial conversion of MoO₆ octahedral units into MoO₄ tetrahedral.