Deep-red activated persistent luminescence nanoparticles via upconversion

In the last few years, few studies using upconversion to charge persistent luminescence were reported in the literature [1] , [2] . One of the suggested ways to do so is to synthesize an upconverting material and a persistent luminescent material and transfer energy radiatively, taking advantage of an overlap between the upconversion emission and persistent luminescence excitation [2] . Within this scheme, we synthesized Zn 1.33 Ga 1.34 Sn 0.33 O 4 :0.5%Cr 3+ (ZGSO), a recently known persistent luminescent material [3] at the nanoscale for the first time through hydrothermal method adapted from Maldiney et al. [4] and NaGdF 4 :Yb 3+ ,Er 3+ nanoparticles by precipitation, adapted from Palo et al. [5] . Both nanoparticles were mixed together by dry impregnation. TEM images of the NaGdF 4 -decorated particles at two scales are shown in Fig. 1a and 1b . The smaller hexagonal-shaped particles are NaGdF 4 :Yb,Er nanoparticles, while the bigger squares are ZGSO nanoparticles.