Functional Persistent Luminescent Thin Films and Glasses: Materials, Processing, and Future Challenges

With large storage capacity, low cost and long storage life, optical holographic storage technology has great application potential to meet the demands of quick data exchange and cold data storage. Accurate and standardized testing procedure of disc storage life about new optical storage media materials has become an important challenge. In view of the new optical storage technology, we discuss and analyze the applicability and limitations of the application of holographic optical disk life test through the existing domestic and foreign disc test standards. Because of materials changing in the holographic disc, we propose and optimize an aging test model and test procedure based on several discs aging test models. And also hope to provide a reference for the establishment of life test standards for holographic optical storage discs.

Electron-trapping materials have attracted a lot of attention in the field of optical data storage. However, the lack of suitable trap levels has hindered its development and application in the field of optical data storage. Herein, Lu3Al5O12:Ce3+ fluorescent ceramics were developed as the optical storage medium, and high-temperature vacuum sintering induced the formation of deep traps (1.36 eV). The matrix based on the garnet-structured material ensures excellent rewritability. By analyzing the thermoluminescence and photostimulable luminescence, it is found that the transition of electrons provided by Ce3+ between the conduction band and trap levels offers the possibility for optical data storage. As evidence of its application, the optical information encoding using 254 nm light and decoding using a light stimulus and thermal stimulus were applied. These findings are expected to provide candidate material for novel optical storage technology, and further promote the development of advanced information storage technology.

In big data center, optical storage technologies have many advantages, such as energy saving and long lifetime. However, how to improve the storage density of optical storage is still a huge challenge. Maybe the multilayer optical storage technology is the good candidate for big data center in the years to come. Due to the number of layers is primarily limited by transmission of each layer, the largest capacities of the multilayer disc are around 1 TB/disc and 10 TB/ cartridge. Holographic data storage (HDS) is a volumetric approach, but its storage capacity is also strictly limited by the diffractive nature of light. For a holographic disc with total thickness of 1.5mm, its potential capacities are not more than 4TB/disc and 40TB/ cartridge. In recent years, the development of super resolution optical storage technology has attracted more attentions. Super-resolution photoinduction-inhibition nanolithography (SPIN) technology with 9 nm feature size and 52nm two-line resolution was reported 3 years ago. However, turning this exciting principle into a real storage system is a huge challenge. It can be expected that in the future, the capacities of 10TB/disc and 100TB/cartridge can be achieved. More importantly, due to breaking the diffraction limit of light, SPIN technology will open the door to improve the optical storage capacity steadily to meet the need of the developing big data center.

Co-Dopant Influence on the Persistent Luminescence of BaAl2O4:Eu2+,R3+

With the increasing demand of optical storage capacity, multi-level (ML) optical storage based on multi-level-amplitude modulation is receiving more and more attention, for it transmits more information ove a fixed bandwidth channel by using the available SNR more efficiently. We proposed an ML optical storage technology in azo LCP film based on polarization angle division. In this paper, the write strategy is developed by a ML write-compensation system that corrects for non-linearities of the data signal. The dynamic transmittance range is extended with the full monotonic range of angle and the varaition of each amplitude level relative to our dynamic range is improved. The experiments of imroved linear and nonlinear 16-level storage in azo LCP are demonstrated. The effects of thickness non-uniformity on linear and nonlinear 16-level storage are discussed.

We review our work on the development of persistent luminescent (PeL) glasses with different compositions. The direct doping method used for preparation of such glasses is explained. Special attention is paid to the stability of the PeL microparticles (MPs) in the glasses during the glass preparation. We demonstrate that the MPs stability is not only sensitive to the melting conditions but also to the glass composition.

Changing the electronic structure of materials by pressure and the accompanying changes in optical properties have attracted scientific interest. We have reported that the energy position of the conduction band (CB) bottom and the crystal field splitting of the Ce3+:5d excited level in Y3Al5-xGaxO12:Ce3+ are changed by applying pressure, which results in the red shifting of the Ce3+:5d → 4f luminescence and the increase of the quenching temperature. We also reported dramatic improvement of the persistent luminescence performance by either Cr3+ or Yb3+ codoping into the Y3Al5-xGaxO12:Ce3+ phosphors. The different trap depths formed by Cr3+ and Yb3+ affect the initial persistent luminescence intensity and the persistent luminescence duration. In this study, the effect of pressure on the persistent luminescence performance was investigated. For the Y3AlGa4O12:Ce3+-Yb3+ phosphor, the slope of persistent luminescence decay curve becomes more gentle with increasing pressure, while for the Y3AlGa4O12:Ce3+-Cr3+ phosphor the slope becomes steeper. These results indicate that the trap depth of Yb3+ becomes deeper and that of Cr3+ becomes shallower with increasing pressure. Based on the pressure-dependence of the luminescence quenching and the trap depth change estimated from the decay slopes, the relative electronic energies of the CB bottom and the Yb2+ (4f14) or Cr2+ (3d4) levels are discussed. The CB bottom energy is increased relative to the ground 1S0 state of Yb2+ with increasing pressure, which results in deepening of the electron trap depth of the Yb2+ state. The opposite tendency of the Cr3+ codoped sample was described by a decreasing tendency of the energy gap between the CB bottom and the Cr2+:eg level, the relative energy level of which is increased by the increase of the crystal field with increasing pressure in the garnet host material, where the electron-trapping Cr2+ ions take the high spin state (t32ge1g) rather than the low-spin state (t42g).

In order to obtain Gd2.97Pr0.03Ga3Al2O12 powders with different crystallite sizes, a modified Pechini (sol–gel) method was used. Powders were then used for the preparation of ceramics by a high-pressure low-temperature sintering method. The impact of crystallite size and pressure applied during the sintering procedure on conventional and persistent luminescence was investigated and analyzed. It was found that the emission color is strictly dependent on the crystallite size, as such phenomenon may be used in the field of advanced anti-counterfeiting. The spectroscopic properties of Gd2.97Pr0.03Ga3Al2O12 were characterized by means of photoluminescence measurements. The kinetics of luminescence were measured in order to analyze the energy transfer between 3P0 and 1D2 excited states that also take an active role in the persistent luminescence process. It was found that an increase in the crystallite size led to a higher energy transfer from the 3P0 to 1D2 level and a change in the emission color. As such, it was studied for potential application in ratiometric optical thermometry. The effect was also investigated in terms of persistent luminescence. It was also found that the sintering pressure causes changes in the crystallographic parameters of the powders and, in consequence, has a great impact on the optical properties of ceramics. The conducted research gives insights into the mechanism of persistent luminescence and expands the application field of optical storage materials.

Wafer-level flexible carbon-based film for fluorescent display and optical information storage

Two-dimensional (2D)-halide perovskites have been enriched over recent years to offer remarkable features from diverse chemical structures and environmental stability endowed with exciting functionalities in photoelectric detectors and phosphorescence systems. However, the low conversion efficiency of singlet to triplet in 2D hybrid halide perovskites reduces phosphorescence lifetimes. In this study, the long persistent luminescence of 2D all-inorganic perovskites with a self-assembled 2D interlayer galleries structure is investigated. The results show that the decay time of the long persistent luminescence increases from 450 s to 600 s, and the luminescence color changes from cyan to orange, and the thermal stability of photoluminescence enhances dramatically after replacing Cd2+ by appropriate Mn2+ ions in 2D Cs2CdCl4 Ruddlesden-Popper phase perovskites. Furthermore, diversified anti-counterfeiting modes are fabricated to highlight the promising applications of Cs2CdCl4 perovskite systems with tunable persistent luminescence in advanced anti-counterfeiting. Therefore, our studies provide a novel model for realizing tunable long persistent luminescence of perovskite with 2D self-assembled layered structure for advanced anti-counterfeiting.

During the past five years, advances in the information-theoretic analysis of "one-dimensional (1D)" recording channels have clarified the limits on linear densities that can be achieved by track-oriented magnetic and optical storage technologies. Channel architectures incorporating powerful codes, such as turbo codes and low-density parity-check codes, have been shown to achieve performance very close to the information-theoretic limits. As 1D track-oriented data storage technologies reach maturity, there is increasing interest in "two-dimensional (2D)" recording technologies, such as two-dimensional optical storage (TwoDOS) and holographic storage. This paper provides an overview of some recently developed techniques for determining analytical bounds and simulation-based estimates for achievable densities of such 2D recording channels, as well as some recently proposed signal processing and coding methods that can move system performance closer to the information-theoretic limits.

Nanoscale silver clusters were prepared in a soda-lime glass matrix through the ion-exchange (Ag+ ↔ Na+) method followed by thermal annealing in oxidizing atmosphere. The effects of annealing time and temperature on the plasmonic response and optical properties of silver nanocluster in glass matrices have been investigated by using UV-visible absorption spectroscopy and photoluminescence spectroscopy. The surface plasmon resonance of silver nanoparticles has been observed in annealed samples. The blue shift has been observed as a function of post-annealing time at a constant temperature. Transmission electron micrographs show the presence of spherical nanoparticles with a maximum particle size of 4-5 nm after annealing, which is consistent with Mie theory based results. The nano-sized Ag nanocluster on glass matrix is suitable as future prospective for potential applications in optical data storage.

Highly efficient photostimulated luminescence of Pb2+ doped SrAl2O4:Eu2+, Dy3+ borate glass for long-term stable optical information storage

(M,Ca)AlSiN3:Eu2+ (M=Sr, Mg) long persistent phosphors prepared by combustion synthesis and applications in displays and optical information storage

Unlocking long-lasting green luminescence in manganese-doped magnesium gallate