Upconversion of erbium

ytterbium co-doped glass were studied. The luminescence spectra in 800nm near-infrared region were analyzed

which is caused by three kinds of transitions. Except for the ordinary

4

F

9/2

→

4

I

15/2

transition

there are another two transitions:

2

H

11/2

→

4

I

13/2

4

S

3/2

→

4

I

13/2

. Effects of Er

3+

concentration on the three transitions are also researched. With 966nm-laser diode as pumping source

we measured the excitation and emission spectra of six bulk glasses with different Er

3+

concentrations with F111AI model fluorescence-meter.Except green and yellow upconversion luminescence(coresponding to the transitions

2

H

11/2

→

4

I

15/2

2

S

3/2

→

4

I

15/2

and

4

F

9/2

→

4

I

15/2

)

there is a luminescence band in 780～850nm in the near-infrared region.The peak at 830nm is apparent and higher with lower concentration.With the Er

3+

concentration increasing

the peak at 830nm disappears while the peak at 800nm becomes apparent. According to the excitation spectra of the samples and the energy levels of Er

3+

we think that the near-infrared upconversion luminescence band consists of three kinds of transitions:

4

S

3/2

→

4

I

13/2

(central wavelength:842nm)

2

H

11/2

→

4

I

13/2

(central wavelength:820nm) and

4

I

9/2

→

4

I

15/2

(central wavelength:800nm).When Er

3+

concentration is low

the populations in

2

H

11

4

S

3/2

levels are more

most of the populations on these two levels will transit to the

4

I

15/2

and emit green light

another part of the populations will transit to

4

I

13/2

level and 830nm light emits. When Er

3+

concentration is higher

because of the increase of the excite-state-absorption(ESA) and non-radiation rate to

4

I

9/2

level as well as the possibility of cross-relaxation from

2

H

11/2

4

S

3/2

to

4

I

9/2

(

2

H

11/2

4

S

3/2

→

4

I

9/2

4

I

15/2

→

4

I

13/2

)

the population in

4

I

9/2

increases while the populations in

2

H

11/2

and

4

S

3/2

levels decrease

so that the transition

4

I

9/2

→

4

I

15/2

(800nm) becomes stronger

surpassing the light intensity from

2

H

11/2

and

4

S

3/2

to

4

I

13/2

.