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Trivalent rare-earth (RE = Eu, Sm) doped transparent nano-glass–ceramics comprising BaYF 5 nanocrystals were successfully obtained by appropriate heat-treatment of the corresponding precursor sol–gel glasses. Their structural and spectroscopic properties were investigated and compared with those for Eu 3+ -doped-BaYF 5 nanocrystals prepared by a solvothermal method. X-ray Diffraction, Transmission Electron Microscopy and Energy Dispersive X-ray Spectroscopy measurements confirmed the distribution of BaYF 5 nanocrystals in the glass matrix, presenting a cubic phase structure with space group Fm - 3m . In order to achieve a further structural characterization, the luminescence properties of the Eu 3+ and Sm 3+ dopants were also used as sensitive probes. The reduction in the emission intensities of hypersensitive transitions 5 D 0 → 7 F 2 and 4 G 5/2 → 6 H 9/2 for Eu 3+ and Sm 3+ ions respectively, along with time-resolved measurements, confirm the distribution of a significant fraction of RE ions into the fluoride nanocrystal environment. These results suggest that BaYF 5 nano-glass–ceramics doped with Eu 3+ or Sm 3+ can be considered as potential red-emitting phosphors for the development of white LEDs under near UV excitation. [ABSTRACT FROM AUTHOR]