We report efficient non-resonant ground state excitation at 1064 nm of trivalent neodymium (Nd$^{3+}$) ions in stoichiometric neodymium aluminum borate NdAl$_3$(BO$_3$)$_4$ nanoparticles, which are crystalline and, besides the large content of Nd$^{3+}$ ions, present excellent photoluminescence properties. Up-conversions (UCs) were observed and the energy pathways identified, as starting by multi-phonon assisted ground state absorption ($^4$I$_{9/2}$-$^4$F$_{3/2}$) and excited state absorption ($^4$I$_{11/2}$-$^4$F$_{3/2}$) with the population of the $^4$I$_{11/2}$ level by thermal coupling with the ground state. The excited state $^4$I$_{11/2}$ is also populated by relaxations of the Nd$^{3+}$ ions increasing the population of the $^4$F$_{3/2}$ level. Cross-relaxation among two Nd$^{3+}$ ions ($^4$F$_{3/2}$,$^4$I$_{9/2}$)-($^4$I$_{15/2}$,$^4$I$_{15/2}$) with subsequent phonon emission leads to two ions at the $^4$I$_{11/2}$ level every iteration triggering a photon avalanche mechanism which greatly enhances the efficiency of the UCs. Ladder thermal excitation $^4$F$_{3/2}$-[$^4$F$_{5/2}$,$^2$H$_{9/2}$]-[$^4$F$_{7/2}$,$^4$S$_{3/2}$]-$^4$F$_{9/2}$ was achieved, and the ground state relaxation from these levels provided emission at 880 nm, 810 nm, 750 nm, and 690 nm, respectively. Energy transfer UCs (Auger) between Nd$^{3+}$ ions at the $^4$F$_{3/2}$ level allowed the population of the [$^2$G$_{3/2}$,$^4$G$_{7/2}$] from which relaxations to the $^4$I$_{9/2}$, $^4$I$_{11/2}$, and $^4$I$_{13/2}$ states provided emissions around 536 nm, 600 nm, and 660 nm, respectively. Associated with the nonradiative relaxations, we observed the heating of the nanoparticles (22 {\deg}C to 240 {\deg}C) with subsequent thermal enhancement of the frequency UCs due to the redistribution of population among coupled energy levels of the Nd$^{3+}$ ions.

中文翻译：

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NdAl3(BO3)4 纳米粒子在 1064 nm 处激发的光子雪崩样上转换

我们报告了化学计量的硼酸铝钕 NdAl$_3$(BO$_3$)$_4$ 纳米粒子中三价钕 (Nd$^{3+}$) 离子在 1064 nm 处的有效非共振基态激发，这些纳米粒子是晶体和, 除了大量的 Nd$^{3+}$ 离子外，还具有优异的光致发光性能。观察到上转换 (UC) 并确定能量路径，从多声子辅助基态吸收开始 ($^4$I$_{9/2}$-$^4$F$_{3/2 }$) 和激发态吸收 ($^4$I$_{11/2}$-$^4$F$_{3/2}$) 与 $^4$I$_{11 /2}$ 级通过与基态的热耦合。激发态 $^4$I$_{11/2}$ 也由 Nd$^{3+}$ 离子的弛豫填充，增加了 $^4$F$_{3/2}$ 的数量等级。两个Nd$^{3+}$离子之间的交叉松弛($^4$F$_{3/2}$,$^4$I$_{9/2}$)-($^4$I $_{15/2}$, $^4$I$_{15/2}$) 以及随后的声子发射导致每次迭代的 $^4$I$_{11/2}$ 水平上的两个离子触发光子雪崩机制，这大大提高了效率的 UC。阶梯热激发$^4$F$_{3/2}$-[$^4$F$_{5/2}$,$^2$H$_{9/2}$]-[$^实现了 4$F$_{7/2}$,$^4$S$_{3/2}$]-$^4$F$_{9/2}$，并且基态弛豫由此水平分别提供 880 nm、810 nm、750 nm 和 690 nm 的发射。在 $^4$F$_{3/2}$ 水平的 Nd$^{3+}$ 离子之间的能量转移 UCs (Auger) 允许 [$^2$G$_{3/2} $,$^4$G$_{7/2}$] 从中放松到 $^4$I$_{9/2}$、$^4$I$_{11/2}$，以及$^4$I$_{13/2}$ 状态分别提供了 536 nm、600 nm 和 660 nm 附近的发射。与非辐射弛豫有关，