The fluorescence decay time of rare earth materials is a very important parameter which characterizes the transition probability between energy levels

the interaction between host lattics and dopant and the energy transfer dynamics in co-doped phosphors

etc.To date many investigations have dealt with the excitation and emission of these solid materials;however

the decay time data are scare and discrepancies exist among published values.The purpose of the present work was to establish an easily available technique for measuring decay times ranging from tens of nanosecond to several milliseconds and to study the energy transfer phenomenon in some luminescent Systems.According to the excitation and emission characteristics of the particular tare eaith ion studied

samples were excited either by the 337 nm radiation of a nitrogen laser or the 532 nm output of a Nd:YAG laser;and the signals were received either by a photomultiplier for the visible fluorescence or a germanium diode for the near infrared emission.Attention was payed to using weak excitation and eliminating random scattering to avoid the interference in measurements.Our photomultiplier was specially wired for high gain

clean transient response by mounting the tube dhectly on a printed circuit board and a low impedance termination of 50 was used.Thus we have obtained the decay time of 68ns for Ce

3+

in Ce:YAG and 42ns in Ce

Nd:YAG

in excellent agreement with the values measured on a SP-70 nanosecond spectrofluorimeter based on time-correlated single-photon counting technique.Shortening of the decay time of Ce

3+

in double-doping system compared to that in single doping one cleaily indicates the energy transfer from Ce

3+

to Nd

3+

in Ce

Nd:YAG.Eu

2+

-doped phosphors studied are of high luminescent efficiency in the blue-green region.The broadness of the emission band indicates the interaction between host and activator which can be attributed to the presence of an excited electron in an outer shell of the Eu

2+

ion.The transitions correspond to 4f-5d.The oscillation strength of these transition are orders-of magnitude higher than those for the normally weak and shielded 4f-4f transitions of Eu

3+

Since the radiative probability of 4f level is low(10

3

s

-1

)compared to that of 5d level(10

6

s

-1

).The decay time Eu

2+

-doped(Sr

Ca)

5

(PO

4

)Cl:Eu

2+

(Eu

Ba)Mg

2

Al

16

O and SrAl

2

O

4

:Eu

2+

is nearly 1 microsecond

and that of EuP

6

O

14

is 4.3 milliseconds.Nd

3+

doped in different tost lattices is one of the most powerful and widely used laser active materials.In the present study the decay times were measured for Nd:YAG

Nd

Ce:YAG

Nd

Cr:YAG and NdP

5

O

14

.We found that the

4

F

3/2

lifetime of Nd

3+

in Ce and Cl co-doped Systems was not noticeably changed as compared to that in single doping system.Nd

3+

has a shorter lifetime in NdP

5

O

14

probably as a lesull of concentration quenching.