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In this paper, we report a facile method to prepare lanthanide-doped Na 3 ZrF 7 upconversion nanoparticles. By using this technique, monodisperse lanthanide-doped Na 3 ZrF 7 nanoparticles of approximately 10 nm in diameter could be synthesized at 260 °C. The Na 3 ZrF 7 :Yb 3+ 20%, Er 3+ 2%, and Na 3 ZrF 7 :Yb 3+ 20%, Tm 3+ 1% nanoparticles exhibited almost pure red and near-infrared emissions, respectively; however, the Na 3 ZrF 7 :Yb 3+ 20%, Ho 3+ 2% nanoparticles exhibited a multiband emission. The special emission output was caused by the cross relaxation of the activator ions, as a rare-earth ion (RE 3+ ) cluster was formed, shortening the distance between the RE 3+ ions. The emission output of the Na 3 ZrF 7 :Yb 3+ 20%, Er 3+ 2% nanoparticles was significantly influenced by the NaOH dosage. The Na 3 ZrF 7 :Yb 3+ 20%, Er 3+ 2% nanoparticles synthesized with a different NaOH dosage of 2.5 mmol showed the most intense total emission intensity among all samples. However, the red/green emission ratio was gradually enhanced as the NaOH dosage increased. [ABSTRACT FROM AUTHOR]