Earlier, it was shown by the EPR method that at a very low concentration of the Nd³⁺ ion in the Nd³⁺:CaF₂ crystal, highly symmetric cubic centers with the O_h symmetry are formed. In the present study, the optical centers of the Nd³⁺ ion with an anomalously long radiative lifetime τ_R = 13.6 ms of the ⁴F_3/2(1) crystal-field (CF) level in the Nd³⁺ (0.05 at.%): Na⁺ (0.2 at.%): CaF₂ single crystal at T = 7 K were detected by the method of time-resolved site-selective fluorescence laser spectroscopy. Its fluorescence excitation at the ⁴I_9/2(1) → ⁴G_5/2(1) transition of Nd³⁺ is in a longer wavelength spectral range compared to optical tetragonal (C_4v) L-, orthorhombic (C_s) pair M-, and quartet N- centers. New optical centers exhibit inhomogeneous splitting and can be attributed to nearly cubic sites with symmetry close to O_h. Also numerous Nd³⁺ optical sites in the Nd³⁺ (0.03 at.%): CaF₂ and Nd³⁺ (0.05 at.%): Na⁺ (0.2 at.%): CaF₂ crystals at T = 7 K with τ_R = 240 μs ‒ 8.5 ms of the ⁴F_3/2(1) CF level of Nd³⁺ were detected in a shorter wavelength spectral range compared to the nearly cubic sites. Among them, the sites with the longest τ_R = 8.5 ms except for the nearly cubic sites, which were identified as C_2v symmetry sites. Their radiative lifetime is about six times that of the C_4v site (τ_R = 1.4 ms). This means that, for optical sites without a center of inversion, the radiative lifetime of the excited state at sites with higher symmetry can be almost an order of magnitude less than at sites with lower symmetry. We explained this result by the different distance between the Nd³⁺ ion and the ion, which compensates for the excess of its charge. Thus, we have demonstrated the use of the Judd-Ofelt approach to explain the difference in the rates of emission of the excited state in different optical sites of the same rare-earth ion in the same crystal matrix.

先前，通过EPR方法显示出，在Nd ³⁺：CaF ₂晶体中的Nd ³⁺离子浓度非常低时，形成了具有O _h对称性的高度对称的立方中心。在本研究中，钕的光学中心³⁺离子与异常长的辐射寿命τ _{- [R}  = 13.6的MS ⁴ ˚F _3/2在钕（1）晶体场（CF）水平³⁺（0.05在 通过时间分辨位点选择性荧光激光光谱法检测到T = 7 K时的Na ⁺（0.2 at。％）：CaF ₂单晶。其荧光激发在Nd ^3+的4 I _9/2（1）→ ⁴ G _5/2（1）跃迁与光学四边形（C _4v）L-，正交（C _s）对M-和四方N中心。新的光学中心表现出不均匀的分裂，并且可以归因于对称性接近O _h的近立方位。在T  = 7 K的Nd ³⁺（0.03 at。％）：CaF ₂和Nd ³⁺（0.05 at。％）：Na ⁺（0.2 at。％）：CaF ₂晶体中还有许多Nd ³⁺光^学位点τ _ř与近立方点相比，在更短的波长光谱范围内检测到Nd ³⁺ 的⁴ F _3/2（1）CF水平为_240μs‒ 8.5 ms 。其中，站点最长τ _ř 除了近立方位点，其被确定为C = 8.5毫秒_2V对称部位。他们的辐射寿命大约六倍的C _4V位点（τ _{- [R}  = 1.4毫秒）。这意味着，对于没有反转中心的光学位点，具有较高对称性的位置处的激发态的辐射寿命可能比具有较低对称性的位置处的激发态的辐射寿命几乎低一个数量级。我们通过Nd ³⁺之间的不同距离解释了这一结果离子和离子，以补偿其多余的电荷。因此，我们已经证明了使用Judd-Ofelt方法来解释在相同晶体基质中相同稀土离子的不同光学位点中激发态发射速率的差异。