Fluoroborate glasses have been the subject of several spectroscopic investigations due to their potential as laser host matrix. In recent letters infrared conversion to visible and ultraviolet by Yb

3+

-Er

3+

and Yb

3+

-Ho

3+

ions in some glasses host has been reported. In this paper

the aim is to find suitable host for upconversion luminescence

and a fluoroborate glass co doped with Yb

3+

and Er

3+

was designed. The optical transition properties and upconversion under 970nm LD excitation were discussed for this glass sample. The fluoroborate glass with component 30H

3

BO

3

-15AlF

3

-19.5PbF

2

-10BaF

2

-10ZnF

2

-10NaF

5

Yb

2

O

3

-0.5Er

2

O

3

was prepared. The absorption spectrum was measured in visible range from 350nm to 700nm. The J-O theory was used to calculate the optical properties of Er

3+

and Yb

3+

codoped in fluoroborate glass. The J-O parameters were obtained

Ω=1.2E-20(cm

2

)

Ω=3.6E-20(cm

2

)

Ω=7.7E-21(cm

2

). The transition probabilities

the oscillator strengths

branching ratios and the radioactive lifetimes were obtained. The red (

4

F

9/2

→

4

I

15/2

) and green (

2

H

11/2

4

S

3/2

→

4

I

15/2

) upconversion luminescence under 970nm LD excitation was observed

the upconversion mechanism was discussed. In this system the upconversion luminescence by energy transfer from Yb

3+

to Er

3+

and from Er

3+

to Er

3+

and excited state absorption of Er

3+

was proposed. The relationship between LD working current and intensity of upconversion luminescence was discussed. The results confirmed that the upconversion process is consisted by two photons.