Introducing and studying origin of deep electron traps in Ba_1-xZrSi₃O₉:xEu for optical data storage

Highlights

• The doping of Eu ions introduces deep electron traps.

• The trap distribution is tunable by atmosphere treatment.

• The deep traps should originate from V_O1 oxygen vacancy.

• Ba_1-xZrSi₃O₉:xEu materials are good candidates for optical data storage.

Abstract

Eu ions doped Ba_1-xZrSi₃O₉:xEu materials are synthesized by solid state reaction method, facing optical data storage applications. The doping of Eu ions introduces deep electron traps at 0.90 eV below the conduction band minimum of Ba_1-xZrSi₃O₉:xEu (1400 °C air). Moreover, the trap distribution is tunable, and there are only deep traps in sample Ba_0·85ZrSi₃O₉:0.15Eu (1400 °C Ar/H₂) with the disappearance of shallow traps. Deep traps can prevent information from loss, while the disappearance of shallow traps can eliminate interference to deep traps by avoiding redeployment of electrons between shallow and deep traps over time. Further, post-sintering in a reducing atmosphere after sintering in the air can increase the concentration of deep traps and deepen the color of samples, while post-sintering in the air after sintering in a reducing atmosphere can obviously decrease the concentration of deep traps and the color of samples return to white from yellow. Experimental results indicate that the deep traps in samples Ba_1-xZrSi₃O₉:xEu should originate from oxygen vacancy defects, which also serve as color centers. First principles calculations show that V_O1 oxygen vacancy defects introduce obvious defect energy levels below the conduction band minimum of BaZrSi₃O₉-V_O1, which further illustrate the deep traps should originate from V_O1 oxygen vacancy defects located at the connection of layer to layer in layered matrix. Ba_1-xZrSi₃O₉:xEu materials with deep electron traps are good candidates for optical data storage.

Introduction

With the rapid development of cloud computing, big data, artificial intelligence and so on, data storage technologies are facing great challenges. Optical data storage technologies have the advantage of low cost, long service lifetime, large capacity, low energy consumption, safety and reliability [[1], [2], [3]]. Blue ray disk is the current mainstream conventional optical data storage technology; however, data storage density is often theoretically restrained due to the diffraction limit of optical system. Traditional optical data storage industry has been overwhelmed, so it is very important to expand new optical data storage technology and develop new optical data storage materials.

Deep electron traps below the conduction band minimum can store electrons after excitation with short wavelength light and can release stored electrons by means of high temperature thermal stimulation or long wavelength light stimulation, that is, they can realize data write-in and read-out, so they have potential applications in optical data storage technology. This kind of optical data storage technology does not solve the problem about diffraction limit of optical system, but by expanding wavelength, intensity or volume of electron trapping materials into multiplexing optical data storage technology, the size of data will be significantly improved by orders of magnitude. The research of electron trapping optical data storage materials has attracted wide attention [[1], [2], [3], [4], [5], [6]]. Lin et al. developed a brand new optical storage medium of transparent glass ceramic embedded with photo stimulated LiGa₅O₈:Mn²⁺ nanocrystals capable of achieving bit-by-bit optical data write-in and read-out in a photon trapping/de-trapping mode [1]. Lin et al. also developed a BaSi₂O₅:Eu²⁺, Nd³⁺ material containing deep electron traps in a narrow distribution, which has potential as efficient optical data storage medium [3]. Many electron trapping optical data storage materials have been developed, however, the lack of materials with excellent optical data storage performance is still the bottleneck that restrains their practical applications.

The narrow deep electron traps are suitable for electron trapping optical data storage materials [2,3]. In this work, we mainly focus on the study of deep electron traps in Ba_1-xZrSi₃O₉:xEu for optical data storage applications. So far, almost all the reported references about Ba_1-xZrSi₃O₉:xEu materials have focused on studying the photoluminescence (PL) or persistent luminescence properties [[7], [8], [9], [10], [11], [12], [13], [14], [15]], but neglecting their possible applications in optical data storage. For example, we have previously reported that Ba_1-xZrSi₃O₉:xEu (x = 0.15) can directly emit nearly white light under the excitation of multi-wavelength ultraviolet radiation, due to the coexistence of multiple luminescent centers and the energy transfer among them [7]. Guo et al. reported that the long-lasting phosphorescence of BaZrSi₃O₉:Eu²⁺,Pr³⁺ could be observed by the naked eye for 15 h in the dark after ceasing the irradiation source, and a series of thermoluminescence (TL) analyses confirmed continuously distributed electron traps in depth of 0.64–0.72 eV [9]. To the best of our knowledge, no reports have tried to apply Ba_1-xZrSi₃O₉:xEu materials on optical data storage. Recently, we find that the doping of Eu ions introduces deep electron traps in Ba_1-xZrSi₃O₉:xEu, and the trap distribution is tunable. This work indicates that Ba_1-xZrSi₃O₉:xEu materials with deep electron traps show great potential in optical data storage applications.