Colloidal TiO

2

was prepared by hydrolyzation of tetra-n-butyl titanate.The prepared TiO

2

powder was heat-treated at 400

600 and 850℃ respectively.The original and the heat-treated TiO

2

powder samples were characterized through thermoanalyses(DTA-TG)

X-ray diffraction(XRD) and photoluminescence(PL) measurements.DTA-TG and XRD data were used to investigate the structural phase transition and check the crystal types.The XRD data indicated that the original sample and the sample heat-treated at 400℃ were mainly brookite

the sample treated at 600℃ was mainly anatase

and the sample treated at 850℃ was mainly rutile.The DTA-TG data and the XRD data suggested that

as the heat-treatment temperature was elevated

the TiO

2

crystals transformed from brookite to anatase and

finally

to rutile and that a first order structural phase transition occurred at 808℃.On the PL spectra of the original powder and the powder samples heat-treated below 600℃

two emission peaks can be observed at 400 nm and 470 nm respectively.The emission at 400 nm could be assigned to the band to band transition.The weaker emission at 470 nm was associated with the surface states of the crystals.With increasing heat-treatment temperature

the size of the TiO

2

particles increased

and the interband emission peak at 400 nm shifted to red.In other words

as the size of the TiO

2

particles decreased

and the interband emission peak at 470 nm shifted to blue

which arose from the quantum-size effect.As the heat-treatment temperature was elevated to 850℃

the emission peak at 400 nm disappeared

the emission peak at 470 nm became the highest peak

and the emission wavelength range(became) narrower obviously.These phenomena were resulted from the changes of TiO

2

crystalline structures.With the increasing heat-treatment temperature

the size of TiO

2

crystals increased.As a result

the quantum-size effect became weaker and weaker

and the number of the structural defects became less.Therefore

the photoluminescence of the samples exhibited markedly changes.