The sample of YLiF

4

:Er

3+

Tm

3+

Yb

3+

is synthesized by hydrothermal method.The mol fraction of Er

3+

Yb

3+

and Tm

3+

is 1%

1.5% and 2%

respectively.The emission of YLiF

4

:Er

3+

Tm

3+

Yb

3+

excited by 355 nm is blue light with the peak in 450 nm which comes from the transition of

1

D

2

3

F

4

of Tm

3+

.After excited by 378 nm

YLiF

4

:Er

3+

Tm

3+

Yb

3+

emits green light with the main peak in 552 nm.The color of upconversion luminescence of YLiF

4

:Er

3+

Tm

3+

Yb

3+

excited by 980 nm is white color.The upconversion spectrum exhibits distinct emission peaks at 665(651)

552(543)

484 and 450 nm.There is another peak around in 648 nm.The strongest is the light with the wavelength of 665 nm(651 nm).The blue light comes from the transition of

1

G

4

3

H

6

and

1

D

2

3

F

4

of Tm

3+

.The green light results from the transition of

4

S

3/2

(

2

H

11/2

)

4

I

15/2

of Er

3+

.It is proved that the red light originates from the transition

1

G

4

3

F

4

of Tm

3+

and the transition of

4

F

9/2

4

I

15/2

of Er

3+

.The excitation spectrum monitored by 665 nm is different to that monitored by 552 nm.There is an excitation peak corresponding to the energy level

1

G

4

of Tm

3+

in the excitation spectrum of 665 nm.But there is no corresponding peak in the excitation spectrum of 552 nm.It is concluded that there is energy transfer processes between Er

3+

and Tm

3+

ions.In the double-log coordinate system

the slope of the emission of 484

552 and 665 nm is 2.25

2.28 and 2.21

respectively.The slope of the emission of 359 nm is 2.85.According to this power law

The emission of 484

552 and 665 nm are all due to two photon process

while the emission of 359 nm is due to three photon process.