掺Tm3+的TeO2-Bi2O3-ZnO玻璃的结构、热学和光谱性质

《Journal of Allergy and Hypersensitivity Diseases》：Structural, thermal and spectroscopic properties of Tm3+ doped TeO 2-Bi 2O 3-ZnO glasses

本研究系统分析了Tm3?掺杂TeO?-ZnO-Bi?O?玻璃的密度、热学和光谱特性，发现其具有低多声子弛豫率（~132 s?1）和较窄OH?含量（1.7×101? ions/cm3）。发射谱在1.85 μm处呈现217 nm宽的发射带，且通过交叉弛豫机制实现激光增益优化。计算表明0.55 mol% Tm3?掺杂浓度时激光增益最大，此时样品密度6.17 g/cm3，玻璃转变温度340 °C，且发射截面达6.9×10?21 cm2。结构分析显示Bi3?的引入促进TeO??1非桥氧结构形成，降低 phonon 能量至747 cm?1。

　　
Tellurite glasses have long been recognized for their unique optoelectronic properties, making them suitable candidates for laser applications in the mid-infrared region. This study systematically investigates the effects of Tm3? doping on the structural, thermal, and spectral characteristics of TeO?-ZnO-Bi?O? glasses, focusing on their potential for 1.9 μm laser operation. The research reveals that optimizing Tm3? concentration can balance laser gain and avoid concentration quenching, while the inherent low phonon energy of tellurite networks enhances the efficiency of rare-earth ion luminescence.

The glass system chosen—TeO?-ZnO-Bi?O?—combines the advantageous properties of tellurite matrices with the redox stability provided by bismuth oxide. Bi3? ions in this system facilitate the formation of non-bridging oxygens (NBOs) through substitution reactions, which reduces phonon energy levels and minimizes non-radiative decay pathways. This structural modification is critical for maintaining the population inversion necessary for laser action.

Key findings include:
1. **Density and Thermal Stability**: Densities increased slightly with Tm3? doping (from 6.16 to 6.22 g/cm3), reflecting the incorporation of heavier Tm3? ions. However, the thermal stability window narrowed significantly (ΔT reduced from 126°C to 59°C), limiting fiber-drawing potential but maintaining bulk laser applicability.

2. **Structural Evolution**: Raman spectroscopy showed progressive depolymerization of the tellurite network as Tm2O? content increased. The 747 cm?1 peak intensity decreased, while the 405 cm?1 band (ascribed to Bi-O-Bi linkages) became relatively more prominent. This indicates increasing NBO fraction with Tm3? doping, reducing the number of bridging oxygen atoms and network connectivity.

3. **OH? Content Reduction**: Infrared absorption measurements demonstrated a 15% reduction in OH? ion concentration at 2.0 mol% Tm2O? doping. This aligns with previous reports showing Bi3? substitution can displace water molecules from the glass structure, improving chemical purity and reducing non-radiative losses.

4. **Optical Properties Enhancement**: The emission spectrum at 1.85 μm exhibited a broad FWHM of 217 nm, which surpasses the 125 nm FWHM of ZBLAN fluoride glasses. This宽带发射源于 tellurite 网络的三维无序结构，提供了更灵活的波长调谐空间。Calculations using the Judd-Ofelt method showed Ω? values ranging from 3.66 to 4.56×10?21 cm2, indicating strong covalent character in Tm-O bonds, crucial for efficient energy transfer.

5. **Cross-Relaxation Dynamics**: Fluorescence lifetime measurements at 1.85 μm revealed a dramatic decrease from 1.25 ms (0.5 mol% Tm) to 0.196 ms (2.0 mol% Tm), attributed to Tm3?-Tm3? cross-relaxation. Calculations using the classic cross-relaxation model (Equation 6) identified an optimal ion concentration of ~2.3×102? ions/cm3 (0.55 mol%), where the product of lifetime and ion density reaches maximum. This corresponds to the 0.5 mol% Tm sample demonstrating the best compromise between gain and quenching effects.

6. **Emission Characteristics**: The 1.85 μm emission band showed minimal spectral shift across doping levels, maintaining a stable profile essential for diode-pumped lasers. The calculated stimulated emission cross-section (σ_SE) reached 6.9×10?21 cm2 at 0.5 mol% doping, comparable to performance observed in phosphate-based glasses.

7. **Gain Spectroscopy**: Effective gain cross-section analysis revealed a tunable emission range from 126 nm to 147 nm FWHM, depending on population inversion. This宽带特性 enables broad-wavelength lasing, with theoretical optimal wavelengths at 1890 nm (β=0.4), 1900 nm (β=0.3), and 1912 nm (β=0.2), providing flexible wavelength selection for different applications.

The study concludes that the 0.5 mol% Tm:TBZ glass represents the optimal balance for 1.9 μm laser operation, with thermal stability and emission properties warranting further experimental validation. Future work is recommended to address fiber-drawing limitations through composition optimization, and to perform direct laser cavity tests to characterize Q-switching and mode-locked potential.

Comparative analysis with other hosts reveals tellurite advantage in combination with Bi3? doping:
- Lower phonon energy (747 cm?1 vs. 880 cm?1 in germanate)
- Higher solubility for Tm3? (up to 2 mol%)
- Broader emission bandwidth (217 nm vs. 125 nm in ZBLAN)
- Higher refractive index (n=2.08 at 1.9 μm vs. n=1.6 in silica)

These properties collectively position TeO?-ZnO-Bi?O?/Tm3? system as a promising platform for next-generation mid-IR lasers, particularly for applications requiring short-pulse generation and wavelength agility in the 1.8-2.0 μm range. The findings advance the understanding of rare-earth ion behavior in complex tellurite matrices, providing a roadmap for designing tailored laser hosts through compositional optimization.