固体材料中稀土离子荧光寿命的研究

本文用激光激发和荧光探测技术测定了Eu2+、Eu3+、Ce3+、Dy3+、Nd3+和Tb3+离子在一些发光材料和激光晶体等固体中的荧光寿命,其寿命值从几十纳秒到几毫秒.为此对寿命测量技术进行了探讨以适应如此宽广的时间范围.从测得的寿命数据解释了材料内激活离子的性质和相互作用.

FLUORESCENCE LIFETIME OF RARE EARTH IONS IN SOLID MATERIALS

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 Ce3+ 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 Ce3+ in double-doping system compared to that in single doping one cleaily indicates the energy transfer from Ce3+ to Nd3+ in Ce,Nd:YAG.Eu2+-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 Eu2+ 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 Eu3+,Since the radiative probability of 4f level is low(103s-1)compared to that of 5d level(106s-1).The decay time Eu2+-doped(Sr,Ca)5(PO4)Cl:Eu2+,(Eu,Ba)Mg2 Al16O and SrAl2O4:Eu2+ is nearly 1 microsecond,and that of EuP6O14 is 4.3 milliseconds.Nd3+ 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 NdP5O14.We found that the 4F3/2 lifetime of Nd3+ in Ce and Cl co-doped Systems was not noticeably changed as compared to that in single doping system.Nd3+ has a shorter lifetime in NdP5O14 probably as a lesull of concentration quenching.