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Spinodal decomposition is a phase-separation phenomenon occurring at non-equilibrium conditions. In isotropic materials, it is expected to improve the physical properties, in which modulated structures arise from a single system of spinodal waves. However, in anisotropic materials this process is controversial and not very well understood. Here, we report anisotropic spinodal decomposition patterns in single crystals of K-rich feldspar with macroscopic monoclinic 2/m symmetry. The periodicity of the spinodal waves at ~450 nm produces a blue iridescence, typical of the gemstone moonstone. Stripe patterns in the (010) plane, labyrinthine patterns in the (100) plane, and coexistence of the two patterns in the (110) plane are first resolved by scanning Rayleigh scattering microscopy. Two orthogonal systems of spinodal waves with the same periodicity are derived from the features and orientations of the patterns on the crystal surfaces. The orthogonality of the waves is related to the perpendicularity of the binary axis and the mirror plane. Thus, the spinodal patterns must be controlled by symmetry constraints during phase separation at early stages. Unusual and new properties could be developed in other anisotropic materials by thermal treatment inducing two orthogonal systems of periodic spinodal waves.

We, herein, report on the radioluminescence and thermoluminescence properties of a sodium-rich feldspar ((Na,K)[AlSi 3 O 8 ]) with a mean molecular composition of orthoclase (Or) and Albite (Ab) of Or 1 Ab 99 . Despite the complexity of the luminescence emissions of the sample, it is possible to determine six different emission bands at about 300, 380, 420, 460, 550 and 680 nm. The 300 nm emission can be associated to structural defects related to the recombination process in which the diffusion of Na ions is involved. The UV-blue emission bands have the following features: (i) the 380 nm, typical of mineral phases containing SiO 4 groups, is related to intrinsic defects in the lattice; (ii) the 420 nm band is associated with the presence of Cu(II) ions close to the hole traps or the recombination on a centre formed from a hole-oxygen atom adjacent to twoAluminum atoms (Al-O-Al) and (iii) the 460 nm waveband is due to the presence of Ti 4+ . The green and red emissions are, respectively, associated with the presence of Mn 2+ and Fe 3+ ions. The ratio between the relative intensities, peaked at 290 (the more intense waveband) and 550 nm is about 10 for both TL and RL, which implies that the efficiency of recombination centres does not change regardless of the type of the process.

The ultraviolet (UV) emission at 290 nm has been studied by thermoluminescence (TL), cathodoluminescence (CL), and radioluminescence (RL) techniques in a natural K-feldspar with intermediate microcline X-ray diffraction pattern. Electron microprobe analyses (EMPA) give the chemical formula K0.98Na0.02Al1.02Si2.98O8. An irregular submicroscopical twinning has been observed from transmission electron microscopy (TEM) images. Selected area electron diffraction (SAED) patterns along the [001] zone axis evidence the triclinic character of this feldspar (γ* angle ≈ 91°) and exhibit a double spot splitting, associated with the presence of discrete twin-domains, interconnected by diffuse streaks. The 29Si MAS NMR spectrum demonstrates that the appearance of this UV emission cannot be explained by distinct T−O−T geometry of the local structure in comparison with other triclinic K-feldspars. The close association between twinning and the UV band in the K-feldspar points to charge trapping and light emissions from complexes of structural defects located at the twin-domain boundaries. The high-temperature slope of the TL glow curve follows a power law decay, suggesting possible trapping−detrapping dynamics related to cooperative phenomena inside the complexes.

The blue thermoluminescence (TL) emission of a complex charoite silicate [K 4 NaCa 7 Ba 0.75 Mn 0.2 Fe 0.05 (Si 6 O 15 ) 2 (Si 2 O 7 )Si 4 O 9 (OH) · 3(H 2 O)], exhibits a continuum in the trap structure similar to that observed in other natural materials; i.e., the glow curve, that consists of a single broad peak at 350 • C, continuously shifts towards higher temperatures when the sample is preheated up to increasing temperatures. This behaviour could be attributed to the charoite strained structure including possible non-bridging oxygen, silicon vacancy-hole centres and Si-O bonding defects which seem to be responsible for this UV-blue emission typical of stressed silicates. The calculation of the activation energy from the TL glow curve performed by the initial rise and the TL glow curve fitting methods are fairly well correlated. The evolution of both the activation energy values and the parameters describing the width of the exponential distribution tends to get larger when increasing the annealing temperatures owing to the emptying of the shallower energy traps.

A partir do uso de matérias-primas convencionais e não convencionais, foram formuladas diversas séries de massas cerâmicas para revestimentos gresificados (isto é, sem carbonato), obtendo seus diagramas de gresificação (absorção de água e retração linear em função da temperatura). As alterações mineralógicas e microestruturais das massas devidas ao processo de queima foram acompanhadas por Microscopia Eletrônica de Varredura. Os resultados mostram que a partir de diferentes tipos de matérias-primas, não só é possível obter massas cerâmicas de grés porcelânico, como também a diminuição da temperatura máxima de queima, mantendo a estabilidade dimensional.