A Facile Approach to Fabrication of Hexagonal‐Phase NaYF₄:Yb³⁺, Er³⁺ Hollow Nanospheres: Formation Mechanism and Upconversion Luminescence

Abstract

Abstract The hexagonal‐phase NaYF 4 :Yb 3+ , Er 3+ hollow nanospheres (HNS) have been successfully prepared for the first time by means of a hydrothermal route with the aid of polyethylenimine (PEI) as a surfactant. The nitrogen adsorption/desorption isotherms demonstrated the porous nature of the NaYF 4 HNS. The formation mechanism was explored based on the effects of the reaction parameters. The NaYF 4 solid spheres underwent a dissolution‐recrystallisation transformation and a hollowing process when the hydrothermal reaction time was prolonged. The localised Ostwald ripening mechanism was proposed to account for the formation of NaYF 4 HNS, in which loose aggregations were found to be crucial. The upconversion luminescence of NaYF 4 :Yb 3+ , Er 3+ HNS was also investigated. It is expected that these NaYF 4 HNS might have potential in applications as building blocks for biolabels and drug‐delivery.