Search

LuP[O.sub.4]: Nd and YP[O.sub.4]: Nd represent new and very fast potential scintillator materials. For most types of ionizing excitation, the luminescence of these materials is dominated by an emission band whose maximum intensity occurs at about 192 nm. The origin of this band lies in the fast 5d--4f transitions of the [Nd.sup.3+] ions. An additional contribution due to host-defect emission varies for different samples. These defects appear to be responsible for the limited light yield of LuP[O.sub.4]: Nd. Index Terms--Luminescence, recombination, scintillation.

In this paper, we report on the scintillation and spectroscopic properties of YAG crystals activated with [Pr.sup.3+] ions. The light yield of this material was found to be dependent on the level of activation. Best results are achieved for nominal [Pr.sup.3+] concentration of 0.24 at.%. Spectroscopic results reveal effects readily explained in the frame of recombinational model of YAG: Pr scintillation. Index Terms--Energy transfer, scintillation, YAG.

The ability of activator ions to capture charge carriers and assume a different charge state under ionizing radiation is essential for efficient performance of rare-earth (RE)-doped scintillator materials utilizing the carrier recombination energy. In this paper the sequence of carrier trapping is discussed and interpreted using a simple, single-configuration-coordinate model for two different cases: In one case (LuP[O.sub.4]:Ce, YAl[O.sub.3]:Ce, LuAl[O.sub.3]:Ce) the charge state involved in the scintillation mechanism is [Ce.sup.4+], while in the other (LuP[O.sub.4]:Yb, YbP[O.sub.4]) it is Y[b.sup.2+]. The possibility of a nonradiative recombination via Ce and Yb ions is also considered and found highly unlikely in accordance with experimental results.

The present status of the LuAl[O.sub.3]:Ce (LuAP) scintillator is reviewed and its performance compared to that of YAl[O.sub.3]:Ce (YAP). The light output of LuAP, at this stage of development, appears to be limited by two factors: insufficient Ce concentration and the presence of a parasitic absorption. Both LuAP and YAP show a dependence of light output on thickness, indicating that YAP also suffers from parasitic absorption. Measurements on undoped material offer a clue to the identity of the 'parasite'.

A new scintillator, LuAl[O.sub.3]:Ce, has been found to have properties that put it in the forefront when stopping power and timing is of importance. This material, an extension of other well known cerium-doped scintillators, the yttrium-based orthoaluminate and garnet, can be readily pulled from the melt, and displays particularly promising performance. We summarize the results achieved when Y is replaced by Lu in this class of oxide crystals.

In this paper we review solved and some of remaining problems in development of Ce[F.sub.3] scintillator. Ce[F.sub.3] emerges as a dense (6.16 g/cc), fast (23 ns), and reasonably efficient (2400 photons/MeV) material with potential applications in high energy and nuclear physics experiments. Despite significant progress in technology the level of uncontrolled impurities and defects in present crystals is still too high, posing problems like scintillation light trapping and radiation damage. We speculate about the possibility of electron self-trapping and nonradiative recombination at Ce sites leading to limited light output and intrinsic radiation hardness of Ce[F.sub.3].