The absorptionand fluorescence measurementswerecarried
out onaShimadzuUV-265absorptionspectrophotomter(Tokyo,
Japan) andaHitachiF-4500spectrofluorometer(Tokyo,Japan),
respectively.Excitationandemissionbandwidthswerebothsetat
10nm.A150Wxenonarclampwasusedastheexcitationlight
source.Astandard1.0cmquartzcellwasused.pHmeasurements
weretakenonaModelpHS-3CpH-meter(ShanghaiRexInstru-
ment Factory,Shanghai,China).