الفهرس 
1. IntroductionOnly 14 pages are availabe for public view
 |  | from | 175 |  |  |
| | | from | 175 | | |
Abstract
In this work, two series of glass samples were prepared:
Series A: 50Bi2O3- 5 MoO3- 45 B2O3- x Dy2O3
where x= (0.05, 0.1, 0.3, 0.5, 0.7, 1) mol %.
Series B: 45B2O3- (50-y) Bi2O3- 5MoO3- y ZnO - 0.7Dy2O3
where y= (5, 10, 15, 20, 25) mol %.
These samples have been successfully prepared by melt quenching technique. All glasses of the two series are yellowish brown. The amorphous nature was checked by XRD. Density, molar volume, oxygen packing density (OPD) and FTIR Spectra (over the wavenumber range of 400 – 4000 cm-1) have been measured and discussed for group (A) and (B). The optical properties, optical band gap, and Urbach’s energy of bulk samples were studied using transmission and absorption spectra in the range of (400 to 1000 nm).
The colorimetric parameters: (CIE( coordinates, correlated color temperature (CCT), and yellow to blue ratio (Y/B) were estimated from the photoemission spectra for both groups (A, B). Judd-Ofelt theory was employed to find oscillator strengths from absorption spectra parameters that are calculated for group (A).
Elemental analysis of the glass samples of group (B) has been carried out using XPS.
Effect of adding Dysprosium oxide (Dy2O3) on the increase of the emission of white light:
The main results of group (A) could be summarized as follows:
➢ XRD confirmed amorphous state of all the studied glasses.
➢ Density was found to increase, and the molar volume decreased with increasing the ratio of doped dysprosium, which reveals that the glass samples became more compact as the Dy2O3 content increased that consequently increase the bridging oxygens bond (BO).
➢ The FTIR data indicated the existence of BiO3, BiO6, BO3, BO4, MoO4, and MoO6 structural groups.
➢ Absorption processes of the rare earth ions Dy3+ have been observed at ” " ~ " ” 758, 806, 900, 1090, 1274 and 1688 nm and were assigned to the Dy3+ ions transitions from the 6H15/2 ground state to 6F5/2, 6H5/2, 6F9/2, 6H9/2, and 6H11/2 excited states, respectively.
➢ The nonlinear change in both the optical band gap and Urbach’s energy is related to the role played by BiO6 units which reflected on the BO3→BO4 conversion and the formation of nonbridging oxygens (NBO).
➢ The excitation spectra of the high concentration glass sample with 1 Dy2O3 mol% was carried out at 575 nm. The spectrum gave six bands at 352, 367, 384, 429, 454, and 476 nm corresponding to the excitation from the ground state (6H15/2) to the excited states (6P7/2, 6P5/2, 4I13/2, 4G11/2, 4I13/2 and 4F9/2) respectively, with high intensity located at 384 nm.
➢ The emission spectra showed three emission bands around 485 nm, 575 nm, and 650 nm corresponding to the 4F9/2→6H15/2, 4F9/2→6H13/2, and 4F9/2→6H11/2 transitions, respectively.
➢ The Y/B ratio was found to be in the range which indicates that all glass samples can be used in the white LED applications.
➢ The estimated color coordinates (x, y) for the glass samples 0.05, 0.1, 0.3, 0.5, 0.7 and 1 mol% Dy3+ were (0.32, 0.32), (0.32, 0.33), (0.31, 0.31), (0.31, 0.31), (0.33, 0.32), and (0.32, 0.31) respectively which confirm that all the glass samples are appropriate for white light generation.
➢ Applying the Judd-Ofelt (J-O) theory, the parameters of J-O: Ωλ (λ = 2, 4, 6) are calculated from absorption spectra. It is found that Ω2 is greater than Ω4 and Ω6 which indicates the position of Dy3+ ion is in asymmetric site with a weak bond with oxygen surrounding it.
Substituting bismuth oxide by zinc oxide:
The main results of group (B) doped with constant Dy3+ ions. [45B2O3- (50-y) Bi2O3- 5MoO3- yZnO - 0.7Dy2O3] could be summarized as follows:
➢ XRD confirmed amorphous state of all the studied glasses.
➢XPS spectral data was utilized to examine the various oxidation states of the different elements in each composition. XPS confirms the constituent of the samples: B, Zn, Bi, Mo, Dy and O elements.
• The peak at 191.72 eV corresponding to B 1s energy level confirms 3+ oxidation state.
• The binding energy of Bi ranges from 158.8 eV to 166.4 eV in all group samples. The peaks deconvoluted into four peaks attributed to Bi04f7/2, Bi3+4f7/2, Bi04f5/2 and, Bi3+4f5/2.
• The binding energy of Dy 3d5/2 and Dy 3d3/2 are 1303 eV and 1330 eV, respectively.
• The XPS of O 1s spectra is used to evaluate the proportions of bridging (BO) and non-bridging (NBO) oxygen atoms for various glass systems.
• The XPS of all samples illustrates the gradual decrease of the (BO/NBO) from 3.3 to 2.8 by the increase of Zinc oxide from 5 to 20 mol% and reaches 1.0 for the sample having 25 mol %.
➢ Density was found to decrease, and the molar volume decreased with increasing the replacement of Bismuth oxide (of density 8.9 g/mol), by Zinc oxide (of density 5.61 g/mol), which reveals that the glass samples became more compact.
➢ Zn-O bond length reported to be in the range of 1.98 to 2 Å, while Bi-O bond length reported to be 2.22 Å, the larger values of the radii and bond length of Bi2O3, compared to those of ZnO, resulted in volume decrement.
➢ The FTIR data indicated the existence of BiO3, BiO6, BO4, BO3, MoO4, and MoO6 structural groups.
➢ Absorption processes of the rare earth ions Dy3+ have been observed at ” " ~ " ” 700, 808, 900, 1086, 1276 and 1674 nm and were assigned to the Dy3+ ions 6F3/2, 6H5/2, 6F7/2, 6H9/2+6H7/2 and 6H11/2 + 6H9/2 transitions from the 6H15/2 ground state, respectively. The 1274 nm band has found to be the hypersensitive transition.
➢ The change in both the optical band gap and Urbach’s energy is related to the role played by BiO6 units which reflected on the BO3→BO4 conversion and the formation of nonbridging oxygens.
➢ The excitation spectra of the high concentration glass sample with 1 Dy2O3 mol% was found at 575 nm. The spectrum observed the six bands at 352, 367, 384, 429, 454, and 476 nm represented the excitation from the 6H15/2 (ground level) to the excited levels: 6P7/2, 6P5/2, 4I13/2, 4G11/2, 4I15/2, and 4F9/2 respectively, with high intensity located at 384 nm.
➢ The emission spectra showed three emission bands around 483 nm, 576 nm, and 650 nm corresponding to the 4F9/2→6H15/2, 4F9/2→6H13/2, and 4F9/2→6H11/2 transitions, respectively.
The stark effect drastically decreased by replacing bismuth oxide by zinc oxide.
➢ The Y/B ratio values indicate that all glass samples can be used in the white LED applications.
➢ The estimated color coordinates (CC) for the glass samples 5, 10, 15, 20, and 25 mol% ZnO were (0.33, 0.32), (0.33, 0.32), (0.34, 0.33), (0.33, 0.32), and (0.32, 0.31) respectively which confirms that all the glass samples are appropriate for white light generation.
The results of group (A) containing different content of Dy3+ ions and group (B) having constant Dy3+ ions and in which ZnO replaces Bi2O3 suggested the possibility of using these materials for future applications in white light generation.