Surface effect is probably the most important factor that makes the spectral properties of rear earth doped nanosized materials different from that of bulk.In many cases

surface acts as a quenching center

that increases nonradiative transition rates of the dopant.Besides

the surface diversifies the local environments of the dopantions

thus the emission spectra of nanosized materials may shift

split or get broadening.In Eu

3+

doped nanoparticles

such a site inequivalency was studied widely with selective excitation.In this report

we show that the temperature dependent emission spectra are also a result of this effect.

5

D

0

7

F

2

emission spectra of Eu

3+

in nanocrystalline YVO

4

at different temperatures were measured with non-selective excitation.At low temperature

the spectrum is a broad band

superposed by a number of spectral lines

while at room temperature

it consists chiefly of two lines similar to that observed in bulk.Referring to the results of selective excitation in YVO

4

:Eu

3+

nanoparticles

we decomposed the emission spectra into two parts:that(

I

C

)from the Eu

3+

ions located near the particle center with the emission similar to that in bulk;and that(

I

S

)from Eu

3+

ions close to the surface with the emission wavelengths extended wider.As the temperature decreases

the relative intensity of

I

S

/

I

C

approaches to a constant 2.3 in our sample with average radius of 27 nm.That gives an estimation of the surface layer thickness

4.5 nm

in which the spectral properties of the Eu

3+

ions are disturbed by the surface.The temperature dependence of

I

S

/

I

C

can be fitted by either an energy transfer process with energy mismatch of 900 cm

-1

or an electron transfer process from the Eu ions to the surface traps across a 900 cm

-1

barrier.The variation of the emission spectra originates from the temperature dependent quenching via surface quenching centers.