image: (a), Digital photographs of precursor glass (PG) and transparent glass ceramics (TGCs) under natural light (top), 254-nm UV light (middle) and thermal stimulation (bottom); in the condition of thermal stimulation, all the samples were charged by 254-nm light in advance for 5 min, delayed for 10 min to eliminate PersL, and then heated to 150 ¡ãC (for TGCs) or 500 ¡ãC (for PG). (b), PSL spectra of PG and TGC heat treated at 750 ¡ãC for different durations. (c), Schematic illustration of the multilayer TGC-configured ODS medium and the write-in/read-out process for optical information. (d), 3D optical data read-out using an 808-nm NIR laser (power density: 1.3 W/mm2) to show the encoded ¡°C¡±, ¡°A¡±, and ¡°S¡± of the binary system (the photos are taken through a 750-nm short-pass filter). (e), 3D optical read-out of the encoded images of Einstein in different layers with the aid of heat (150 ¡ãC). (f), Wavelength multiplexing by combining 4 TGC species with various heat treatment times into one system, where the multicolour encoded Chinese characters with the meaning of ¡°good fortunes¡±, English characters, and QR code can be read-out by heating. (g), Demonstration of the intensity multiplexing by varying the input UV irradiation power. Note: the time lags set to take photographs are 3 s for heating and 1 s for turning on the 808-nm laser. view more
Credit: by Shisheng Lin, Hang Lin, Chonggeng Ma, Yao Cheng, Sizhe Ye, Fulin Lin, Renfu Li, Ju Xu, Yuansheng Wang
Currently, the heritage of human civilization depends on the preservation of digitalized information, including character, image, audio and video, which spawn countless data. The resulting information explosion stimulates the continuous upgrade of the storage medium and mode. In this context, magnetic data storage has been gradually replaced by optical data storage (ODS) with higher efficiency, lower energy consumption, larger capacity, and longer service lifetime. As a classical kind of ODS medium, photostimulated (PSL) materials with persistent luminescence have attracted researchers' interest since their discovery because of their good erasable-rewritable ability and ultrafast writing speed. Nevertheless, PSL materials are still not in consideration as an alternative to big data storage media due to their difficulties in achieving nanocrystallization--the light-matter interaction on the micron scale would result in a small writing/reading resolution to a great extent; moreover, the micro-sized PSL material is hard to be made transparent, and so can only be used for 2D ODS with data write-in/read-out on the surface. There are two mutually contradictory aspects for attaining a nanosized PSL material: on the one hand, high temperature is required to induce suitable deep traps in the host responsible for the charging/releasing of charge carriers (electrons or holes) during data encoding/decoding and, on the other hand, high temperature is known to result in severe particle coarsening and agglomeration.
In a new paper published in Light Science & Application (Light: Science & Applications, 2020, 9: 22), scientists from the Key Laboratory of Optoelectronic Materials Chemistry and Physics, Key Laboratory of Design and Assembly of Functional Nanostructures, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, China, and co-workers developed a new kind of ODS medium, PSL transparent glass ceramic (TGC), via in situ precipitation of PSL LiGa5O8: Mn2+ NCs (2-7 nm) from a glass matrix. The controlled thermally driven glass crystallization leads to a highly ordered nanostructure in the glass network, while the self-limited growth of LiGa5O8: Mn2+ NCs facilitates the generation of deep defects for PSL at a relatively low temperature due to low ionic diffusion mobility and, thus, the balance between nanosized grains and PSL performance is leveraged. The highly ordered nanostructure enables light-matter interaction with high encoding/decoding resolution and low bit error rate. Importantly, going beyond traditional 2D optical storage, the high transparency of the studied bulk medium makes 3D volumetric optical data storage (ODS) possible, which brings about the merits of expanded storage capacity and improved information security.
These scientists evaluated the theoretical memory density of the developed PSL TGC 3D-ODS medium:
"Ideally, if we perform data encoding based on a confocal microscopy system with a 254 nm write-in laser diode and a common 0.85 NA focusing lens, the lateral and axis resolutions are 119 nm and 492 nm, respectively, and so the volume of a voxel is 7.0¡Á10-15 cm3(translating to ~130 Tbit/cm3). One can expect a higher ODS density when using advanced far-field super-resolution optical microscopy to break the optical diffraction limit."
"Moreover, in the studied PSL material, wavelength multiplexing can be realized by combining different TGC species with various heat treatment times into one system, and intensity multiplexing is attained by changing the input UV irradiation power. It is worth mentioning that the intensity could be perceived as a new dimension, where the greyscale encoding in each voxel enables the storage of information transform from a binary system to a multibinary system." they added.
"This work hopefully brings a renaissance to classical PSL materials and stimulates the development of new multi-dimensional ODS media." the scientists forecast.
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