Alicja Chruścińska

The Church of St James in Toruń is one of Poland's most valuable Gothic monuments. According to the inscription preserved in the presbytery, the commonly accepted date when construction began is AD 1309. However, another hypothesis can also be found in the literature stating that the first brick temple in the location of the present church was built at a much earlier time. In this study, we apply luminescence dating to more than 30 bricks to support that supposition. Our age results suggest that a brick temple was erected on a plan corresponding to the present one in the 13th century.

The importance of the fast decaying signal of quartz for dating sediments is confirmed by years of research. In OSL dating, the single-aliquot regenerative-dose (SAR) protocol is applied to estimate age. The OSL signal measured in this protocol consists of components with different properties, particularly with different susceptibility to bleaching in sunlight. It is known how complicated it is to extract the fast decaying signal from other overlapping signals when blue light is used for stimulation. Decomposing OSL curves into components is unsuitable for dating purposes due to the challenges involved in handling many OSL curves for age estimation and obtaining consistent results across these curves. An OSL measurement method based on optical stimulation while the sample is heated, so-called thermally modulated OSL (TM-OSL), was recently implemented in the SAR protocol. Instead of the blue light (470 nm) in SAR (hereinafter referred to as SAR BLSL), red light (620 nm) is used for optical stimulation. In the protocol with TM-OSL measurement, the fast component is isolated and used for the OSL age determination. The advantage of this approach for a set of samples selected from various depositional environments is presented. The equivalent dose for the same samples was also determined using the SAR protocol that involved red light stimulation (620 nm, SAR RLSL) at an elevated temperature (230°C). The obtained results by the protocols using red light (SAR TM-OSL and SAR RLSL) are compared with the ones determined using the SAR BLSL protocol. Using TM-OSL in the SAR protocol leads to more precise dating results. The shape of the TM-OSL curve for the fast OSL component in quartz allows to identify in the TM-OSL a contribution from a signal of another origin. It prevents age underestimation by excluding from calculations the share of OSL components, which can be less stable.

Trap stability is essential in luminescence dating and thermochronometry. Trap depth and frequency factors determining the stability of the fast component of optically stimulated luminescence (OSL) in quartz, which is the most important in dating, have yet to be uniquely determined, especially for samples with an OSL signal not dominated by this component. One can determine them in OSL thermal depletion curve (OTDC) experiments. The separation of the fast OSL signal undisturbed by other OSL components is vital for obtaining accurate parameters for the traps of interest. This work presents a method of simultaneous thermal and optical stimulation using red light (620 nm) to separate the fast OSL component (the thermally modulated OSL method—TM-OSL). The OTDC experiment with the TM-OSL stimulation was used for the trap parameter determination on a variety of quartz samples, leading us to report for the first time, the trap parameters for the fast OSL component analytically separated in quartz from rock samples. The results obtained for these samples with the fast component of low intensity are consistent with those with an intensive fast OSL component. Results of OTDC measurements for all investigated quartz samples were tested for a wide range of irradiation doses.

Fundamental effects such as the participation of crystal lattice vibrations should be taken into account while considering photo-ionisation in solids at measurement temperatures characteristic for dosimetric applications. The impact of these effects on the optically stimulated luminescence (OSL) can be recognised for example by changes in the optical cross-section of the trap with the stimulation energy and the temperature. The OSL signal observed during the stimulation with variable energy, during the linear heating of a sample or during the stimulation with modulation of the shape of a spectral band can provide important information about the properties of the trap. Moreover, such methods when applied with carefully selected experimental parameters enable the effective separation of the OSL signal originating from different traps. The consequences of such an approach to optical stimulation will be presented using the modelling of the OSL process and compared with experimental results.