Under the excitation of 980 nm laser and 808 nm laser

the upconversion luminescence of ZBLAN:Yb

3+

Tm

3+

is detected. The mol fraction of Yb

3+

Tm

3+

is 3% and 1%

respectively. The emission of ZBLAN:Yb

3+

Tm

3+

is blue light with the peak at 476 nm which comes from

1

G

4

3

H

6

transition of Tm

no matter excited by 980 nm

808 nm and both 980 nm and 808 nm

but the emission intensity is different. The emission intensity co-excited by both 980 nm and 808 nm is much stronger than that excited by 980 nm or 808 nm only. This phenomenon can be explained by luminescence mechanism. Under the excitation of 980 nm or 808 nm

the emission of 476 nm is three photon or two photon process

respectively

while in the 980 nm and 808 nm co-excitation system

the emission of 476 nm is due to one photon process.