Cross-relaxation among neighboring emitters normally causes self-quenching and limits the brightness of luminescence. However, in nanomaterials, cross-relaxation could be well-controlled and employed for increasing the luminescence efficiency at specific wavelengths. Here we report that cross-relaxation can modulate both the brightness of single upconversion nanoparticles and the threshold to reach population inversion, and both are critical factors in producing the ultra-low threshold lasing emissions in a micro cavity laser. By homogenously coating a 5-μm cavity with a single layer of nanoparticles, we demonstrate that doping Tm³⁺ ions at 2% can facilitate the electron accumulation at the intermediate state of ³H₄ level and efficiently decrease the lasing threshold by more than one order of magnitude. As a result, we demonstrate up-converted lasing emissions with an ultralow threshold of continuous-wave excitation of ~150 W/cm² achieved at room temperature. A single nanoparticle can lase with a full width at half-maximum as narrow as ~0.45 nm.

相邻发射器之间的交叉松弛通常会导致自猝灭并限制发光的亮度。然而，在纳米材料中，交叉松弛可以得到很好的控制，并可以用来增加特定波长的发光效率。在这里，我们报道了交叉松弛既可以调节单个上转换纳米粒子的亮度，又可以调节达到种群反转的阈值，这两者都是在微腔激光器中产生超低阈值激光发射的关键因素。通过用单层纳米颗粒均匀地覆盖5μm空腔，我们证明以2％掺杂Tm ³⁺离子可以促进电子在³ H ₄的中间状态下的积累并有效地将激光阈值降低一个数量级以上。结果，我们证明了上转换的激光发射具有在室温下实现的〜150 W / cm ²的连续波激发的超低阈值。单个纳米粒子可以以最大宽度的一半窄至〜0.45 nm的波长发射激光。