Influence of preheating treatment on the luminescence properties of adularia feldspar (KAlSi3O8)

During the firing of ceramics that contain alkali feldspar grains (up to 900 deg. C in bricks and 1200 deg. C in porcelains) the metastable equilibrium of these natural materials is altered (refractory minerals, neo-formed minerals and new glassy components). Hence, potassium rich feldspar lattices, which are being used in some routines of archaeological dating and retrospective dosimetry, suffer minor modifications by preheating and irradiation treatments (K-self-diffusion, stretching, etc.). In this paper, some pre-heatings of a K-feldspar (adularia) from Saint Gothard (Switzerland) attempted to simulate the temperatures and conditions undergone in brick manufacturing processes (1000 deg. C for 24 h and 1200 deg. C for 240 h). Some changes in the behavior of the TL and RL spectral curves were detected after combinations of thermal pretreatments (at 400 deg. C for 48 h; 500 deg. C for 72 h; 600 deg. C for 96 h and 700 deg. C for 144 h) and irradiations. Comparisons between high temperature annealed (1000 and 1200 deg. C) and non-annealed adularias show spectacular changes in the shape of the TL glow curves: natural-irradiated adularia displays a single large peak at ∼100 deg. C, whereas annealed adularias show a very complex structure. The observed modifications, probably due to thermal alkali self-diffusion through the lattice interfaces, tilting of the Al-Si crankshafts and phase exsolutions, have been detected by X-ray diffraction