Xihong Hao

Nondestructive up-conversion readout in Er/Yb co-doped Na0.5Bi2.5Nb2O9-based optical storage materials for optical data storage device applications

Luminescence modulation based on photochromic reactions is always considered to be a promising method to achieve nondestructive readout in photochromic materials. Generally speaking, two conventional strategies have been widely used to achieve this target: tuning the absorption bands and adjusting luminescent quenching mechanisms. In this paper, we found a new strategy to improve effectively luminescence readout capability in Er/Yb codoped NBN-based solid-state inorganic photochromics by using a two-photon absorption mode of luminescent centers. Upon alternating visible light irradiation (407 nm) and the thermal stimulus, the materials exhibited a high luminescence switching contrast ratio (ΔRt = 86%), excellent reversibility, and significantly improved luminescent efficiency (22 times). Most importantly, the photochromic reaction process can be efficiently read out using the two-photon absorption (or up-conversion) mode without inducing any new reactions, showing extremely low destruction on information recording (destruction degree <11%), which is superior to other luminescence emission modes (down-shifting or down-conversion). These results could be used as a guide to tailor the luminescence modulation properties of photochromic materials to realize non-destructive readout in 3D optical data storage device applications.

Luminescence photoswitching of Ho-doped Na0.5Bi2.5Nb2O9 ferroelectrics: the luminescence readout process

Luminescent switching materials upon photochromic reactions have potential applications in optical switching and high-density optical data storage in optoelectronic devices. To avoid interference and destruction of information in practical data storage applications, a nondestructive luminescence readout is essential. However, it is still unclear how to select the optimized excitation and emission bands to avoid the photochromic reaction during the “reading” process while maintaining high luminescence contrast and stability in inorganic photochromic materials. On the basis of the nonradiative energy transfer mechanism, Ho3+ ions were introduced into the Na0.5Bi2.5Nb2O9 host to obtain efficient luminescence switching due to their special excitation (451 nm) and emission (547 nm) characteristics. Under 407 nm irradiation (“writing”), the photochromic phenomenon can be effectively read out by measuring the changes in the luminescence emission intensity. The luminescence switching contrast increased up to 94%. Importantly, the excitation and emission energies did not significantly induce new photochromic reactions, causing less destruction to the material and the luminescence readout process. This outcome is superior to our previously reported results. Furthermore, the luminescence switching properties exhibit hardly any degradation after undergoing several cycles of the “writing”, “reading” and “erasing” processes, indicating excellent reversibility.

(K,Na)NbO3 ferroelectrics: a new class of solid-state photochromic materials with reversible luminescence switching behavior

In this paper, we reported a new photosensitive material, Sm doped K0.5Na0.5NbO3 (KNN) ceramics, fabricated using a solid-sate reaction method, which exhibits both photochromism and luminescence switching properties. By alternating visible light irradiation (λ > 407 nm) and thermal stimulus, the samples show a reversible color change from the initial green to pale gray. Interestingly, luminescence emission intensity can be effectively tuned using photochromic reactions. Furthermore, the luminescence switching degree strongly depends on the firing temperature. These results suggest that KNN-based perovskite oxides with photochromism, luminescence switching and ferroelectric energy storage properties are particularly attractive for optical data storage applications as multi-functional materials.

Giant energy-storage density and high efficiency achieved in (Bi0.5Na0.5)TiO3–Bi(Ni0.5Zr0.5)O3 thick films with polar nanoregions

The development of electronic devices towards integration, miniaturization and environmental friendliness has propelled much recent research on lead-free dielectric capacitors for energy storage, however, high energy-storage density is still an extremely challenging objective for lead-free dielectric materials. Here, a novel lead-free relaxor ferroelectric (1 − x)(Bi0.5 Na0.5)TiO3–xBi(Ni0.5Zr0.5)O3 (BNT–xBNZ, x = 0–0.5) thick film (1 μm) was fabricated by a water-based sol–gel method. Doping of BNZ into the BNT host promoted the formation of polar nanoregions (PNRs), whose domain switching became easier, leading to an improved energy-storage performance. Surprisingly, an ultrahigh recoverable energy density of 50.1 J cm−3 and a high energy-storage efficiency of 63.9% under 2200 kV cm−1 were achieved simultaneously with x = 0.4, which are both more than 100% higher than those of the pure BNT sample. This excellent energy-storage performance can be perfectly comparable with that of lead-based films. Furthermore, the BNT–0.4BNZ thick film showed strong fatigue endurance after 6 × 107 cycles, and it possessed good thermal and frequency stability. The pulsed discharge current waveform demonstrated that the BNT–0.4BNZ thick film showed a very fast discharge speed (210 ns). This study shows that BNT-based materials have an unexpected role as a lead-free family in the field of energy storage and could stimulate the design and fabrication of BNT-based dielectrics with ultrahigh energy-storage performance.