Fig . S1 EDX analysis of Eu 0.95 Tb 0.05 F 3 hexagon-shaped sub-microcages. Fig. S2 The LaMer diagram. Fig. S3 FT-IR spectrum of Eu 0.95 Tb 0.05 F 3 hexagon-shaped sub-microcages. Fig. S4 SEM and TEM images of the samples show the coarsening and morphological evolution of (NH 4 ) x Eu 0.75 Tb 0.25 F (3+x) hollow sub-microspheres. Fig. S5 TEM images of Eu 0.95 Ln 0.05 F 3 (Ln = Y, Gd, Dy, Ho, Er, and Tm) alloyed hexagon-shaped sub-microcages. Fig. S6 TEM images of EuF 3 :Ln 3+ /NH 4 + (Ln = Y,

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... , Dy, Ho, Er, and Tm) alloyed hollow sub-microspheres. Fig. S7 XRD analysis of EuF 3: Ln 3+ and EuF 3 :Ln 3+ /NH 4 + (Ln = Y, Gd, Dy, Ho, Er, and Tm) alloyed hollow architectures. Fig. S8 Relevant energy levels and transitions involved in the cross-relaxation and energy-transfer processes in EuF 3: Ln 3+ and EuF 3 :Ln 3+ /NH 4 + (Ln = Dy, Ho, Er, and Tm) alloyed hollow architectures. Electronic Supplementary Material (ESI) for CrystEngComm This journal is