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Distribution of oxidation states of Cr ions in Ca or Ca/Mg co-doped Cr:Y3Al5O12 single-crystal fibers with nitrogen or oxygen annealing environments |
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| Authors: | Cheng-Nan Tsai Kuang-Yao Huang Hann-Jong Tsai Jian-Cheng Chen Yen-Sheng Lin Sheng-Lung Huang Yen-Sheng Lin |
| Institution: | aInstitute of Electro-Optical Engineering, National Sun Yat-Sen University, Kaohsiung 804, Taiwan bInstitute of Photonics and Optoelectronics, National Taiwan University, Taipei 106, Taiwan cInstitute of Photonics and Optoelectronics and Department of Electrical Engineering, National Taiwan University, Taipei 106, Taiwan dDepartment of Electronic Engineering, I-Shou University, Kaohsiung 840, Taiwan |
| Abstract: | The valence states of Cr ions in Ca or Ca/Mg co-doped Cr:Y3Al5O12 (YAG) single-crystal fibers are studied. The fibers were grown using the laser-heated pedestal growth method, followed by annealing treatments up to 1500 °C. The concentrations of the Cr3+ and Cr4+ ions in octahedral and tetrahedral sites in oxygen or nitrogen environments were characterized. Above 700 °C, migration of Cr4+ between octahedral and tetrahedral sites takes place; its relative stabilization energy was estimated. For Ca,Cr:YAG annealed in an oxygen or nitrogen environment, it was 0.25 and 0.3 eV, respectively. For Mg,Ca,Cr:YAG annealed in oxygen or nitrogen, it was 0.47 and 0.49 eV, respectively. For the Ca,Cr:YAG crystal fiber (Ca/Cr=113.1%) with oxygen annealing, about 35% and 2.5% of Ca ions took part in charge compensation for Cr4+ in the octahedral and tetrahedral sites, respectively. The density of oxygen vacancies depends on the concentration of Ca ions. The estimated ratios of the unreacted oxygen vacancies to total oxygen vacancies were about 63% and 88% for oxygen and nitrogen annealing, respectively. The main limitation on the concentration of Cr4+ in the tetrahedral site of YAG is the presence of unreacted oxygen vacancies. |
| Keywords: | A1 Doping A1 Optical microscopy A2 Laser heated pedestal growth |
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