There has been an intense interest in the investigation of ultra-fine and nanocrystalline oxide upconversion materials these years for potential applications in upconversion phosphors

detectors for infrared radiation

fluorescent labels for sensitive detection of biomolecules and two-photon confocal-microscope imaging. Numerous host materials

such as Y

2

O

3

Gd

2

O

3

ZrO

2

TiO

2

and BaTiO

3

have been investigated as host material for upconversion phosphors due to their low phonon-vibration frequencies. Er

3+

doped materials are well suitable for upconversion because the metastable levels

4

I

9/2

and

4

I

11/2

of Er

3+

can be conveniently popu-lated by low-cost high-power 800 nm and 980 nm laser diodes

respectively. The sensitization of Er

3+

doped materials by Yb

3+

ions is a well-known method for increasing the optical pump efficiency because of the high absorption cross section of Yb

3+

ions around 980 nm and the efficient energy transfer from Yb

3+

to Er

3+

ions. Strontium titanate (SrTiO

3

) is a well-known material because of its good properties

such as its high dielectric constant

high charge storage capacity

good insulating property

its chemical and physical stability and its excellent optical transparency in the visible range. In addition

similar to BaTiO

3

its phonon-vibration frequency is quite low

which makes it suitable for host material as upconversion phosphors. But to the best of our knowledge

there is no reports on upconversion of Er

3+

doped

Er

3+

/Yb

3+

-codoped SrTiO

3

powders. Er

3+

-doped and Er

3+

/Yb

3+

-codoped SrTiO

3

ultra-fine powders have been prepared in a molten NaCl flux. The structure properties of the samples were examined by X-ray diffraction (XRD);Fourier transform infrared spectroscopy (FT-IR) and field emission scan electron microscopy (FE-SEM). FT-IR spectra showed that SrTiO

3

powders may have higher upconversion luminescence efficiency because of its low phonon-vibration frequency. The intense green and red emissions around 528

550 and 663 nm corresponding to the

2

H

11/2

→

4

I

15/2

4

S

3/2

→

4

I

15/2

and

4

F

9/2

→

4

I

15/2

transitions of Er

3+

ions were observed under excitation by 980 nm. Laser power dependence and rare earths ions concentration dependence of the upconverted emissions were investigated to understand the upconversion mechanisms. Excited state absorption and energy transfer process were discussed as the possible mechanisms for the visible emissions.