Spectroscopy and energy transfer in metal ion doped glasses

摻雜金屬離子玻璃的光譜與能量傳遞

Student thesis: Doctoral Thesis

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Author(s)

  • Hongli WEN

Detail(s)

Awarding Institution
Supervisors/Advisors
Award date3 Oct 2012

Abstract

This thesis had three major aims. The first one was to investigate the effect of the dielectric medium upon the spontaneous emission rate using tripositive europium ion-doped lead borate glass. The second aim was to investigate the spectral properties of metal ion-doped glass. The dopant ion was a lanthanide ion or transition metal ion. The host glasses were lead borate glass and sodium borosilicate glass. The third aim was to study the luminescence properties and energy transfer process between ions doped into these glasses. The dopant ions were lanthanide ions or lanthanide-transition metal ion pairs. The following describes these works briefly. 1. The effect of the dielectric medium upon the spontaneous emission rate. The effect of the dielectric medium upon the spontaneous emission rate was investigated using lead borate glass of various compositions lightly doped with Eu3+. A dual approach used the variation of (i) electric dipole/magnetic dipole (ED/MD) emission rates from spectral integrations; and (ii) absolute ED emission rates from lifetime measurements for comparison with the variation of the refractive index of the glass medium. Contrary to a previous study Phys. Rev. Lett. 91, 203903(2003), the results show the relevance of the virtual cavity-model in this case. The MD emission rates were taken to follow the n3 increase in density of photon states in the medium. The justifications for employing Eu3+ for identifying the appropriate model are given. 2. Spectral properties of metal ion-doped glass A. Europium ion-doped lead borate glass. The emission spectra of the tripositive lanthanide ion Eu3+ have been employed to probe its environment in the solid state, and the intensity ratio of magnetic dipole (5D0 → 7F1) and forced electric dipole (5D0 → 7F2) transitions has been used to estimate the "degree of asymmetry" of a crystal site. From the site-selective, low temperature emission spectra of Eu3+ doped into a glass, a new empirical relation has been found between the width of spectral features and the relative intensity of the 5D0 → 7F0 zero phonon line. In order to explain the observations from experiments with excitation at different wavelengths, a generic quantitative relation has been developed from basic theory and validated from our experimental results. This work gives a deeper insight and understanding of the spectral characteristics of Eu3+ electronic spectra in the visible region. The relationship between the band width of luminescence spectral features and their relative intensities has also been investigated, using glasses doped with europium, Eu3+, over a wide composition range. Glasses of composition (B2O3)70(PbO)29(0.5Eu2O3)1 and (B2O3)z(PbO)99.6-z(0.5Eu2O3)0.4 (z = 20, 30, 40, 60, 70), were prepared by the melting-quenching technique. Variable-wavelength measurements by the prism-coupling method enabled interpolation of refractive index at selected wavelengths. Diffuse reflection spectra confirmed the incorporation of Eu3+ into the glass and scanning electron microscopy displayed that this was in a homogeneous manner. Vibrational spectra showed a change in boron coordination from BO3 to BO4 units with increase of B2O3 content in the glass. Multi-wavelength excited luminescence spectra were recorded for the glasses at temperatures down to 10 K and qualitative interpretations of spectral differences with change of B2O3 content are given. The quantitative analysis of 5D0 luminescence intensity-bandwidth relations showed that although samples with higher boron content closely exhibit a simple proportional relationship with band intensity ratios, as expected from theory, the expression needs to be slightly modified for those with low boron content. The Judd-Ofelt intensity analysis of the 5D0 emission spectra under laser excitations at low temperature gives Ω2 values within the range from (3.9-6.5) × 10-20 cm2, and Ω4 in the range from (4.1-7.0) × 10-20 cm2, for different values of z. However, no clear monotonic relation was found between the parameter values and composition. The Judd-Ofelt parameters are compared with those from other systems doped with Eu3+ and are found to lie in the normal ranges for Eu3+-doped glasses. The comparison of parameter values derived from the 10 K spectra with those from room temperature spectra for our glasses, which are fairly constant for different compositions, shows that site selection occurs at low temperature. B. Transition metal ion-doped sodium borosilicate glass and lead borate glass. The UV-Vis-NIR absorption and the luminescence properties of transition metal (3d (Ti → Zn), 4d (Nb, Mo, Ru and Rh), 5d (Ta, W, Re and Ir)) ion-doped sodium borosilicate glass were investigated, as well as transition metal (3d (V → Zn), the two 4d (Mo and Rh) and the three 5d (W, Re and Ir)) ion-doped lead borate glass. Transition metal ions produced intense broad absorption bands and moved the absorption edge of the doped glass to longer wavelength with increasing content of dopant ion in the glass. On the other hand, transition metal ions gave no, or weak, emission in the visible region, which may result from the high phonon energy of the host glass, the inability to populate luminescent states, or other quenching mechanisms. V, Cr, Mn, or Mo ion-doped glasses have been further investigated by the X-ray absorption near-edge structure (XANES) technique to study the valence states existing in the glass. Synchrotron radiation has been used to excite above the band gap of the host glass to study the higher energy levels of the corresponding transition metal ions, but the results do not indicate luminescence from the transition metal ions. 3. Energy transfer and luminescence studies between ions in glasses. A. Pr3+, Yb3+ pair in lead borate glass Lead borate glass samples doped with the tripositive lanthanide ions Pr3+ and Yb3+ were synthesized by the conventional melting-quenching method. The luminescence properties and energy transfer process from Pr3+ to Yb3+ were investigated. Upon ultraviolet excitation, the room temperature luminescence decay curve of a sample containing only a low concentration of Pr3+ exhibited monoexponential decay from 1D2 with the lifetime 37 μs, without emission from 3P0. The room temperature Pr3+ emission intensities decreased with the increase of Yb3+ mole ratio in the glass. Under the excitation of 454.5 nm at 10 K, a broad red emission band centered at 605 nm, and an NIR emission band at 995 nm were observed in the co-doped lead borate glass, originating from Pr3+ and Yb3+ ions, respectively. The decay curves of the 1D2 emission from Pr3+ with addition of Yb3+ in lead borate glass show non-monoexponential character, and are best described by a stretched exponential function. The average 1D2 decay time decreases considerably with the addition of Yb3+ in the glass. Decay curve fitting using a modified Inokuti-Hirayama expression indicates dipole-dipole energy transfer from Pr3+ to Yb3+, which is consistent with the expected cross-relaxation scheme. There is a good agreement of the estimated overall energy transfer efficiency obtained from the integrals under the normalized decay curves, or from the lifetimes fitted by the stretched exponential function, or from the average decay times. B. Pr3+, Yb3+ pair in sodium borosilicate glass Sodium borosilicate glass samples doped with the tripositive lanthanide ions Pr3+ and Yb3+ were synthesized by the conventional melting-quenching method. The luminescence properties and energy transfer process from Pr3+ to Yb3+ were investigated. Upon ultraviolet excitation, the room temperature luminescence decay curve of two samples containing only a low or relatively higher concentration of Pr3+ exhibited biexponential decay from 1D2 without emission from 3P0. The room temperature Pr3+ emission intensities decreased with the increase of Yb3+ mole ratio in the glass. Under the excitation of 454.5 nm at 10 K, a broad red emission band centered at 625 nm, and an NIR emission band at 995 nm were observed in the co-doped sodium borosilicate glass, originating from Pr3+ and Yb3+ ions, respectively. The decay curves of the 1D2 emission from Pr3+ with addition of Yb3+ in sodium borosilicate glass show non-monoexponential character, and are best described by a stretched exponential function. The average 1D2 decay time decreases considerably with the addition of Yb3+ in the glass. C. V5+, Eu3+ pair in sodium borosilicate glass Vanadium doped sodium borosilicate glasses were synthesized using V2O3 and V2O5 as the starting vanadium source, respectively. The absorption and luminescence properties of the V2O3 (or V2O5), Eu2O3 single or co-doped glass were investigated. The absorption intensity in the spectral region of 520-1500 nm increased with increase of V2O3 mole ratio in the glass; or by doping the same mole ratio of V2O3 instead of V2O5 in the glass; or by addition of Eu2O3 into the glass co-doped with V2O5. Addition of V2O3 gave the same absorption edge in the glass, as that for V2O5 at the same mole ratio, both shifting the edge to longer wavelength; while addition of Eu2O3 gave sharp characteristic absorption peaks of Eu3+ and had no effect on the absorption edge in the glass. Glass containing only a lower concentration of V2O5 gave the least absorption intensity in region of 520-1500 nm, and relatively strongest emission at ~526 nm, indicating the existence of V4+ playing a quenching role. The red emission from Eu3+ or broad emission centered at ~524 nm from V5+, when codoped Eu2O3 and V2O3 (or V2O5) in the glass, decreased in intensity to a large extent, indicating quenching of V5+ emission by V4+ and weak exchange energy transfer from V5+ to Eu3+ in the glass. Exceptionally, under excitation of 362 nm, glass containing both low concentrations of V2O3 and Eu2O3 produced broad emission centered at 526 nm and red emission with both almost unchanged intensity relative to the glass single doped lower concentration of V2O3 or Eu2O3. No further obvious energy transfer has been found between 5+V Eu3+ in the glass, still probably resulting from the existence of V4+ acting as a quencher and weak exchange interaction between V5+ and Eu3+ in the glass.

    Research areas

  • Glass, Spectra, Energy transfer, Metal ions