掺雜稀土離子對玻璃的微觀結構與發光性質的 影響

EFFECTS OF RARE EARTH DOPING ON THE MICROSTRUCTURE AND LUMINESCENCE CHARACTERISTICS OF GLASS

江志鈞(Chih-Chun Chiang)

指導教授 ： 徐錦志

大同大學/工程學院/材料工程學系所/博士(2010年)

摘要

近年來，發光玻璃材料引起高度的重視，尤其在光電領域廣泛應用。例如，固態雷射與光通訊元件等。多樣化玻璃系統中，磷酸鹽玻璃具有高稀土離子溶解率與低成形溫度，因此被廣泛的研究。文獻亦指出，玻璃中若形成微觀結構，可改變稀土離子所處之環境 (例如，玻璃或晶體相)，並利用光散射提高稀土離子的發光強度。本研究目的係摻雜高濃度稀土離子於具微觀結構 (例如，結晶與相分離)之硼矽酸鹽與磷酸鹽玻璃的發光特性。

(a) 添加不同稀土離子對Na2O-B2O3-SiO2玻璃的相分離與光學性質的影響
本研究係觀察不同稀土元素 (Er、Eu與Nd)、濃度(0 – 3 mole%)與添加P2O5 (0與2 mole%)對Na2O-B2O3-SiO2玻璃的微觀結構、光學吸收與發光性質的影響。實驗結果發現，添加P2O5、增加稀土含量與改變稀土種類皆可促進Na2O- B2O3-SiO2玻璃的相分離傾向。P2O5-containing的Na2O-B2O3-SiO2玻璃相分離是由矽酸鹽玻璃基地中析出含有稀土聚集之磷酸鹽液滴相。相分離程度越高，同時促進光散射效應 (提高光致發光強度)與濃度淬火效應 (降低光致發光強度)。

(b) 成份變化對摻Er3+的R2O-B2O3-SiO2 (R = Li、Na與K)玻璃的相分離與發光性質的影響
本研究係觀察不同鹼金族元素 (R = Li、Na與K)、Er2O3濃度 (0 – 3 mole%)與添加P2O5 (0與2 mole%)對R2O-B2O3-SiO2玻璃的微觀結構、光學吸收與發光性質的影響，且探討微觀結構與光學性質的關係。實驗結果發現，液滴相的形成同時促進光散射效應 (提高光致發光強度)與濃度淬火效應 (降低光致發光強度)。因此，Er2O3含量對Er3+ 4I13/2 → 4I15/2 躍遷的光致發光強度變化，主要受光散射與濃度淬火效應的相互抵銷所影響。添加1 mole% Er2O3與P2O5-containing的半透明Na2O-B2O3-SiO2玻璃具有最佳微觀結構與最高的光致發光強度。

(c) Er3+ 添加對SnO-P2O5玻璃的結構、熱性質與結晶特性的影響
本研究開發出新型態摻Er2O3 (0 – 8 mole%)的SnO-P2O5玻璃。實驗結果發現，當Er2O3含量為2 – 4 mole%，玻璃的物理、熱學性質與結晶現象呈現不連續。此外，當Er2O3含量≤ 0.5 mole%，玻璃再加熱溫度高於膨脹儀軟化點 (375oC)會在表面形成錫-磷酸鹽結晶相，並導致玻璃破裂。添加更多Er2O3 (1 – 8 mole%)可完全抑制表面結晶，並有助於玻璃成形製程。

(d) 單摻Er3+與共摻Er3+/Yb3+對SnO-P2O5玻璃的發光特性的影響
本研究係觀察單摻Er2O3 (0 – 8 mole%)與共摻Er2O3與Yb2O3 (總和為 1 – 7 mole%)對SnO-P2O5玻璃的吸收截面、光致發光與上轉換強度的影響。稀土含量增加，玻璃結構由焦磷酸鹽 (Q1)轉變為正磷酸鹽 (Q0)。當稀土含量總和大於4 mole%時，由SnO-P2O5玻璃基地析出ErPO4與(Yb, Er)PO4晶體，對此吸收截面、光致發光與上轉換強度扮演重要角色。對單摻Er3+玻璃而言，Er2O3含量對光致發光特性的變化是明顯不同於一般摻雜稀土的玻璃。此結果歸因於光散射所需的ErPO4晶體數量隨Er2O3含量增加而升高，且晶體中Er-Er間距固定所致。對於Er3+/Yb3+共摻玻璃而言，當Yb2O3最佳含量為6 mole% (~1.81×1021 ions/cm3)，光致發光強度可提高14.7倍。當進一步提高Yb2O3含量，結果會導致光致發光強度減弱，這可由自發性的能量傳遞 (APTE)上轉換效應來說明。

(e) Er3+添加對ZnO-P2O5玻璃的結構、熱性質與發光特性的影響
本研究為觀察摻Er2O3於ZnO-P2O5玻璃對性質的影響。實驗結果發現，Er2O3含量增加，玻璃結構由焦磷酸鹽 (Q1)轉變為正磷酸鹽 (Q0)。當Er2O3含量≥ 4 mole%，由ZnO-P2O5玻璃基地析出ErPO4結晶相。ZnO-P2O5玻璃的物理與熱性質則隨Er2O3含量增加呈線性變化。折射率為1.60-1.63之ZnO-P2O5玻璃的光致發光強度高於折射率1.78-1.81為之SnO-P2O5玻璃，此與預估折射率與受激放射截面呈正比的結果不同。這是因ZnO-P2O5玻璃結構的離子堆積比值較大，則相對降低Er–O的共價性，亦提高自發放射機率。

關鍵字

玻璃 ； 微觀結構 ； 稀土 ； 光致發光

並列摘要

In recent years, luminescent glass materials have attracted great attention, especially application for the solid state laser and amplifier devices. In various glass systems, phosphate glass has been widely studied because of it has high solubility of rare earth and low melting/forming temperatures. Moreover, some literatures reported that formation of microstructure in the glass matrix can change the environment of rare earth (such as in glass and crystalline phase). Photoluminescence intensity can be enhanced due to the light-scattering effect in the microstructural glass, which increases the population of rare earth ion on the high energy level. The purpose of this study is to explore the luminescence characteristic of the microstructural borosilicate and phosphate glasses doped with high content rare earth. The results are as follows:

(a) Compositional Dependence of Phase Separation and Photoluminescence in Rare Earths-Doped Sodium Borosilicate Glasses
In this study, the effects of the kind of rare earth (Er, Eu, and Nd), rare earth concentration (up to 3 mole%), and P2O5 addition (0 and 2 mole%) on the phase separation, optical absorption, and photoluminescence (PL) of the sodium borosilicate glasses were investigated. It was found that adding P2O5, increasing rare earth content and changing the kind of rare earth can enhance the phase separation of Na2O- B2O3-SiO2 glass. Adding P2O5 results in the simultaneous segregation of rare earth and P in sodium phosphate droplets. As a consequence, rare earth-bearing phosphate crystals developed within the droplets. Development of the droplet phase enhances both the light-scattering effect (enhancing the PL intensity) and the concentration quenching effect (reducing the PL intensity).

(b) Compositional Dependence of Phase Separation and Photoluminescence in Er3+-Doped Alkali Borosilicate Glasses
In this study, the effects of the kind of alkali (Li, Na, and K), Er2O3 concentration (up to 3 mol%), and P2O5 addition (0 and 2 mole%) on the phase separation, optical absorption, and photoluminescence (PL) of the alkali borosilicate glasses were investigated. The relationship between microstructure and optical properties of the glasses is discussed. It was found that the development of the droplet phase enhances both the light-scattering effect (enhancing the PL intensity) and the concentration quenching effect (reducing the PL intensity). As a result, the variation of the PL intensity of the Er3+ 4I13/2 - 4I15/2 transition with Er2O3 content is mainly caused by the conflict between the light-scattering effect and the concentration-quenching effect. The 1 mole% Er2O3-doped, P2O5-containing, sodium borosilicate glass has the optimum microstructure and thus the highest PL intensity.
(c) Effects of Er3+ Doping on the Structure, Thermal Properties, and Crystallization Behavior of SnO-P2O5 Glass
In this study, a new type of Er2O3–doped SnO–P2O5 glass with Er2O3 content of 0 – 8 mole% has been obtained. It was found that physical properties, thermal properties, and crystallization behavior of the glass exhibit discontinuities at Er2O3 content of 2 – 4 mole%. It was also noted that reheating the glass at 375°C, which is higher than the dilatometric softening temperature, results in the crystallization of a tin phosphate phase from glass surface when Er2O3 content is ≤ 0.5 mole%, resulting in serious cracking of the glass. Adding more Er2O3 (1 – 8 mole%) totally suppresses the surface crystallization, thus it is helpful to glass shaping processes.

(d) Photoluminescence Characteristics of Er3+ Doped and Er3+/Yb3+ Co-Dpoed SnO-P2O5 Glass
In this study, effects of Er2O3 (0 – 8 mole%) doping and Er2O3 and Yb2O3 co-doping (total 1 – 7 mole%) on the absorption cross-section, PL, and upconversion intensities of the SnO-P2O5 glass have been investigated. Precipitation of ErPO4 and (Yb, Er)PO4 crystalline phase in the SnO-P2O5 glass matrix when the total rare-earth oxide content is > 4 mole% plays an important role in determining the absorption cross-section, PL, and upconversion intensities. For Er3+-doped glass, the variation of PL characteristic with the Er2O3 content is obviously different from that for general rare-earth-doped glasses. This result is explained in terms of the light-scattering effect caused by the ErPO4 crystals and the constant Er-Er distance in ErPO4 crystals with the increasing Er2O3 content. After co-doping with Yb2O3, the PL intensity of the glass is enhanced by about 14.7 times at the optimum Yb2O3 content of 6 mole% (~1.81×1021 ions/cm3). Further increase in the Yb2O3 content results in the reduction of PL intensity which can be explained in terms of the APTE upconversion effect.

(e) Effects of Er3+ Doping on the Structure, Thermal Properties, and Photoluminescence Characteristics of ZnO-P2O5 Glass
In this study, Er2O3–doped ZnO–P2O5 glass with Er2O3 content of 0 – 4 mole% has been obtained. It was found that the fraction of Q0 (orthophosphate)-Q1 (pyrophosphate) structure increase in ZnO-P2O5 glass with the Er2O3 content increased. When Er2O3 content is 4 mole%, crystalline particles of ErPO4 have precipitated within the ZnO-P2O5 glass matrix. The physical and thermal properties of the glass linearly increased with increasing Er2O3 content. According to the result, absorption cross-section and PL intensity of the ZnO-P2O5 glass are higher than that of SnO-P2O5 glass, because of the ZnO-P2O5 glass has high ionic packing ratio which reduces the covalency of Er-O bond, and then increases the spontaneous emission probabilities. This result does not conform to the expectation, namely the stimulated emission cross-section of laser glass does not increase with the increasing refractive index.

並列關鍵字

Glass ； Microstructrue ； Rare Earth ； Photoluminescence

參考文獻

2. A. Kitai, Luminescent Materials and Applications, pp. 1-222. John Wiley, Hoboker, 2008.

4. A.J. Kenyon, "Review: Recent Developments in Rare-Earth Doped Materials for Optoelectronic," Prog. Quantum Electron., 26 [4-5] 225-84 (2002).

5. P. Urquhart, "Review of Rare Earth Doped Fiber Lasers and Amplifiers," IEEE Proc., 135 [6] 385-407 (1988).

8. E. Snitzer, "Optical Maser Action of Nd+3 in a Barium Crown Glass," Phys. Rev. Lett., 7 [12] 444-46 (1961).

9. C.J. Koester and E. Snitzer, "Amplification in a Fiber Laser," Appl. Opt., 3 [10] 1182- 86 (1964).