Over the past decades

there has been a significant interest in the production of new materials for multicolor displays.A new technique for solid-state color displays has been developed based upon infrared to visible frequency upconversion in lanthanide doped materials.The three primary colors red

green and blue can be obtained from upconversion luminescence of Er

3+

Pr

3+

Ho

3+

and Tm

3+

etc.However the relative intensities of the three primary colors are still required to control.Thus

it is necessary to develop novel mate-rials capable of multicolor upconversion and investigate their upconversion mechanisms of rare earth ions employed.Rare earth doped fluoride crystals is one of the most attractive materials for near-infrared to visible upconversion because its low phonon energies.In this work

we present intense multicolor upconversion luminescence in Er

3+

/Tm

3+

codoped NaYbF

4

.The relation between upconversion intensity of three fundamental colors and the dopant concentration was discussed and the corresponding upconversion mechanism was proposed.The generation and control of the primary colors through upconversion of Tm

3+

and Er

3+

in NaYbF

4

with single excitation(980 nm)were obtained.The hexagonal NaYbF

4

:Er

3+

NaYbF

4

:Tm

3+

NaYbF

4

:Er

3+

/Tm

3+

upconverting phosphors have been prepared by hydrothermal method under 220℃ for 48 h.The crystal structure and luminescent properties were investigated by using powder X-ray diffraction

diffuse reflectance absorption spectra and fluorescent spectra.The result of powder XRD spectra reveals that Er

3+

and Tm

3+

ions can incorporate completely into hexagonal NaYbF

4

lattice at any concentration by mild hydrothermal method.The diffuse reflectance absorption spectra shows that the absorption peak band centered at 957 nm corresponds to

2

F

7/2

2

F

5/2

transition of /Yb

3+

ion for NaYbF

4

and the absorption peaks of NaErF

4

or NaTmF

4

could be assigned to the transitions from ground state of Er

3+

(

4

I

15/2

)or Tm

3+

(

3

H

6

)to excited states.Under 980 nm excitation

hexagonal NaYbF

4

:Er

3+

can emit strong green and

red emission

which correspond to(

2

H

11/2

4

S

3/2

)

4

I

15/2

4

F

9/2

4

I

15/2

transition of Er

3+

respectively.NaYbF

4

:Tm

3+

exhibit intense blue upconversion emission

which is attributed to

1

D

2

3

F

4

and

1

G

4

3

H

6

transition of Tm

3+

.The emission intensity of blue transitions(

1

G

4

3

H

6

1

D

2

3

F

4

)is enhanced considerably as increasing Yb

3+

content and reach the optimum at NaYbF

4

:Tm

3+

.We agree with the view that the excitation is mobile within the NaYbF

4

lattice

it could thus readily reach the Tm

3+

traps

which cause the high relative intensity of the two blue emissions(

1

G

4

3

H

6

1

D

2

3

F

4

).Tm

3+

and Er

3+

ions can be easily codoped in NaYbF

4

lattice through the mild hydrothermal route

and an energy transfer between Tm

3+

and Er

3+

exists under 980 nm laser excitation:

1

D

2

(Tm

3+

)+

4

I

15/2

(Er

3+

)

3

F

4

(Tm

3+

)+

4

S

3/2

or

2

H

11/2

(Er

3+

)

1

G

4

(Tm

3+

)+

4

I

15/2

(Er

3+

)

3

H

6

(Tm

3+

)+

4

S

3/2

or

2

H

11/2

(Er

3+

).The relative ratio of green

red and blue emission intensity can be tuned by defining Tm

3+

and Er

3+

ion concentration in the NaYbF

4

lattice

and through which

a white light simulation could be obtained in the Tm

3+

and Er

3+

codoped NaYbF

4

.