The possibility to obtain two blue photons under excitation of one VUV photon in NaGdF

4

:Tm

3+

Dy

3+

has been investigated by means of spectroscopic techniques

based on quantum cutting principle.In this compound visible quantum cutting is achieved through downconversion

i.e.

by making use of energy transfer between different lanthanide ions.Upon VUV excitation in the 4f

10

5d levels of Tm

3+

part of the energy is transferred directly from the Tm

3+

4f

10

5d states to Gd

3+

.The cross-relaxation between Gd

3+

-Tm

3+

is followed

and then the left energy is transferred from Gd

3+

to Dy

3+

.Two visible photons are yielded:one from Tm

3+

due to

1

G

4

3

H

6

transition

and one from Dy

3+

due to

4

F

9/2

6

H

15/2

transition.In this paper

the possibility to obtain a new quantum cutting phosphor with higher efficiency

higher stability and higher VUV absorption based on NaGdF

4

:Tm

3+

Dy

3+

has been investigated.The spectroscopic techniques

including luminescent emission

excitation

decay

etc

.were performed to characterize the donor Gd

3+

ion-acceptor Dy

3+

ion energy transfer preceded by energy migration among Gd

3+

lattices in NaGdF

4

doped with different concentrations of Dy

3+

ions.It is shown by the results that the Gd

3+

-Dy

3+

transfer preceded by energy migration among the Gd

3+

ions is mainly governed by the exchange interaction.By the theory on excited state relaxation processes

which was developed by Burshtein

et al

.

the donor-acceptor energy transfer parameter kDA can be calculated from the

6

P

7/2

emission decay of Gd

3+

.The quantum efficiency of Gd

3+

-Dy

3+

energy transfer was derived as well.Powders of NaGdF

4

:Tm

3+

(1.5%) and NaGdF

4

:Tm

3+

(1.5%)

Dy

3+

(0.3%) were prepared by the hydrothermal technique

and NaGdF

4

:Dy

3+

(0.3%

0.6%

1%

3% and 5 %) by the method described in Ref.[4].The emission and excitation spectra were measured by home-made VUV spectrometer and F4500 monochromator.The decay curves were obtained under excitation of OPO laser.The quantum efficiencies for the Gd

3+

-Dy

3+

energy transfer have an optimal value for acceptor concentrations at about

N

A

=0.6% and concentration quenching can be observed obviously.