Abstract We have systematically studied the structural evolutions of trivalent holmium ion (Ho3+) doped potassium gadolinium tungstate (KGd(WO4)2) crystals by means of the CALYPSO structure search method coupled with first-principles calculations. The unbiased global minimum structure search is successful in reproducing the standardized monoclinic structure with C2/c phase for KGd(WO4)2. For the first time, the lowest energy structure of Ho3+-doped KGd(WO4)2 system is identified, which possesses a significantly different monoclinic configuration with P2 space group. It is found that the impurity Ho3+ ions can substitute the sites of Gd3+ ions, forming the [HoO8]13− local units with C2 site symmetry. Our electronic calculations show that the energy band gap of Ho3+-doped KGd(WO4)2 is equal to 3.03 eV. The impurity of Ho3+ ion remains the insulating character of Ho:KGW system. These results could provide important information for understanding the structural evolution and electronic properties of other rare-earth-doped materials.

中文翻译：

---

对 Ho3+ 掺杂的钨酸钾钆的微观结构和电子特性的理论洞察

摘要 我们利用CALYPSO 结构搜索方法结合第一性原理计算，系统地研究了三价钬离子(Ho3+) 掺杂的钨酸钾钆(KGd(WO4)2) 晶体的结构演化。无偏全局最小结构搜索成功地重现了 KGd(WO4)2 具有 C2/c 相的标准化单斜结构。首次确定了掺杂 Ho3+ 的 KGd(WO4)2 系统的最低能量结构，其具有显着不同的单斜晶构型和 P2 空间群。发现杂质Ho3+离子可以取代Gd3+离子的位点，形成具有C2位点对称性的[HoO8]13-局域单元。我们的电子计算表明，Ho3+ 掺杂的 KGd(WO4)2 的能带隙等于 3.03 eV。Ho3+离子的杂质保留了Ho:KGW系统的绝缘特性。这些结果可以为理解其他稀土掺杂材料的结构演变和电子特性提供重要信息。