Abstract
Bone has photoluminescent characteristics that can aid the analysis of thermally altered human skeletal remains as part of the forensic anthropological investigation. Photoluminescence stands collectively for fluorescence and phosphorescence. Because the difference in lifetime between fluorescence and phosphorescence is usually in the range of nano- to microseconds, it is only possible to visually determine whether bone phosphoresces when the lifetime is long enough to be observed. For this study, a distinction was made between long-decay and short-decay phosphorescence. So far, it was unknown whether (thermally altered) human bone emits long-decay phosphorescence after being illuminated and, thus, whether phosphorescence contributes to the observed photoluminescence. If so, whether the observable phosphorescence is dependent on temperature, exposure duration, surrounding medium, bone type, skeletal element, and excitation light and could aid the temperature estimation of heated bone fragments. In this study, bone samples were subjected to heat in the range of from room temperature to 900 °C for various durations in either air or adipose as surrounding medium. In addition, different skeletal elements of a human cadaver were recollected after cremation in a crematorium. Both sample collections were illuminated with light of different bandwidths and visually inspected for phosphorescence and photoluminescence. The samples were scored by means of a scoring index for the intensity of long-decay phosphorescence and photographically documented. The results show that thermally altered human bone fragments do phosphoresce. The observed phosphorescence is more dependent on temperature than on exposure duration, surrounding medium or skeletal element. Of the used wavelength bands, ultraviolet light provided the most temperature-related information, showing changes in both phosphorescence intensity and emission spectrum. Long-decay phosphorescence and fluorescence with short-decay phosphorescence coincide; however, there are also temperature-dependent differences. It is therefore concluded that phosphorescence contributes to the observable photoluminescence and that the visibly observable phosphorescent characteristics can aid the temperature estimation of cremated human skeletal fragments.
Highlights
Altered human bone has photoluminescent characteristics [1,2,3,4,5]
Thereafter, the phosphorescence intensity decreased with increasing exposure temperatures of up to 900 °C, and some samples heated to 900 °C did not emit light after excitation
The visibly observable long-decay phosphorescence intensity and emission bandwidth mostly depend on the exposure temperature and excitation bandwidth and less on the exposure duration and surrounding medium during heat exposure
Summary
Altered human bone has photoluminescent characteristics [1,2,3,4,5]. These characteristics can aid the search for human skeletal remains in difficult contexts. To the retrieval of human skeletal remains, the photoluminescent characteristics can be helpful when interpreting the degree of thermal destruction and thereby indicating the temperature that bone has been subjected to [1, 3]. The estimated temperature that bone reached during a fire can be used to reconstruct the peri- and postmortem events and to substantiate the decision on whether samples are still eligible for molecular analysis, i.e., DNA- or isotope analysis [2, 6,7,8].
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