as solvent for synthesis of nano zno by precipitation method add 3 41 g zncl 2 into 100 g melten caprolactam purity of caprolactam u2267 80 moisture u2266 20 and stir at 150 u00b0 c for 30 min to make zncl 2 fully dissolved when stirring rapidly add 2 g naoh and keep at constant temperature of 100 u00b0 c for 2 h wash the obtained mixture with 200 g deionized water by centrifugation for three times and obtain nano zno powder after intensive drying and crushing fig8 is the x ray diffraction diagram xrd of synthetic nano zno powder with the method in this embodiment and positions and intensity of all the diffraction peaks perfectly match the jcpds card 36 1451 of zincite zno in the database indicating that the product is high purity zno moreover diffraction peak broadening is generally due to particle size refinement indicating that the synthetic zno is small in particle size however diffraction peak intensity is still high indicating that the synthetic material has high degree of crystallinity and is very applicable to luminescent materials fig9 is sem image of synthetic nano zno powder with the method in this embodiment and the observation results show that zno powder is composed of spherical particles of about 8 nm in diameter and can be used for semiconductor luminescent quantum dots use of valerolactam as solvent for synthesis of nano zno by precipitation method add 3 41 g zncl 2 into 100 g melten valerolactam purity of valerolactam u2267 80 moisture u2266 20 and stir at 150 u00b0 c for 30 min.