Alumina is very important ceramic material;it has a unique combination of mechanical and optical properties.Alumina single crystal (sapphire) is commonly used as transparency window in shock wave mea-surements.When doped with Cr

3+

alumina is used as a pressure calibrant in static high pressure experiments.In addition it is believed to be one of the major constituent of the Earth’s mantle.Understanding of its optical property under high pressure is very important for the use of it in high pressure experiments and other material regions.However

sapphire or other transparent windows are indispensable in shock temperature measurements of opaque material.Recently

a few of sapphire’s emission at lower than 50 GPa pressure range had been reported;whether this phenomenon detected at higher pressures is yet an open question.In this paper

infrared radiation of shock loaded sapphire has been observed to 172 GPa

using 1 ns time-resolved photomuhiplier.As an un-polished 20-micro-thickness copper foil being sandwiched by two sapphires for a shock target

the intensity received by photomnltiplier demonstrates a durative increase characteristic.It is the fact that thermal diffusion occurred at contact interface can’t cause this intensity-amplified current

the observed radiance continuously increases with time must origin from sapphire window.Under 130～172 GPa

the near infrared radiance of sapphire increases with shock stress.The fitting curve shows the absorptive parameter varies from 0.8 to 2.1 cm

-1

at 850 nm in the experimental pressure range.Up to now

there is no quantitative calculation about the color temperature of shocked sapphire for explaining this emission.In the previous works

inhomogeneous hot spots distributed in shocked sapphire are regarded as the radiance source of sapphire

these hot spots

named"adiabatic shear band"

are yielded by high speed local deformation.To our interpretation

adiabatic shear band usually exists in high-speed shock compressed material;its survival time depends upon the thermal conduction.Because thermal conduction of sapphire is obviously smaller than that of metals

as such shear band’s temperature can keep a high value in the period of experiment;and this temperature may also track the melting line which is suggested by D.E.Hare(2002).Therefore

obvious emission can be observed from residual heated spots behind shockwave.Based on the mechanism of local deformation

we made a preliminary quantitative model to explain the inhomogeneous emission of sapphire.This mathematic model is derived from an established slipping band theory by D.E.Grady (1982);the calculation shows the model can predict the unique temperature or apparent emission of shocked sapphire.In addition

sapphire’s slipping band temperature in calculation is roughly consistent with the emission temperature values estimated by D.P.Sebbana (2005) and D.E.Hare at lower pressures.In other words

the shear band’s temperature tacitly assumed that the emission is generated by the disjunet heated regions in sapphire window

not by sapphire’s total bulk.The difference of sapphire’s emissivity between the lower pressure and the more than 100 GPa pressure reveals that the density of emission eenters increases with pressure.Therefore

over 100 GPa pressure

sapphire’s radiation may disturb the intedaeial temperature measurement under shock compression.