NaGdF

4

nanocrystals were prepared using a polyol method and were characterized by powder X-ray diffraction (XRD) patterns

field emission scanning electron microscopy (FE-SEM) images and FTIR spectra. Down-conversion luminescence of NaGdF

4

:1%Eu

3+

nanocrystals and up-conversion luminescence of NaGdF

4

:6%Yb

3+

1%Er

3+

nanocrystals were studied. Annealed samples were compared with unannealed samples. The X-ray diffraction results showed that the prepared samples were hexagonal phase of NaGdF

4

. Field emission scanning electronic microscopy revealed that the average diameter was 15

18 and several hundreds nanometers for nanocrystals unannealed

annealed at 400℃ and annealed at 600℃ respectively. After being annealed at 400℃ for 2 h

5

D

1-3

/

5

D

0

emission intensity ratio increased remarkably for NaGdF

4

:1%Eu

3+

sample; up-conversion emission intensity increased at least by factor of 67 for NaGdF

4

:6%Yb

3+

1%Er

3+

sample. These increases were attributed to the anneal-derived decrease of OH

-

species etc. These species have high energy vibrations and can make multiphonon relaxation occur easier. The oxygen contamination is at very low level

undetectable by optical spectroscopy method in samples unannealed and annealed at 400℃

but is detectable by optical spectroscopy method in sample annealed at 600℃. Two-photon processes are involved in the green and red upconversion luminescence and three-photon are involved in the blue upconversion luminescence.