Gupta Santosh K, Modak B, Das Debarati, Modak P, Yadav A K, Sudarshan K
Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai-400085, India.
Phys Chem Chem Phys. 2021 Aug 28;23(32):17479-17492. doi: 10.1039/d1cp02349g. Epub 2021 Aug 6.
Defect engineering in perovskites has been found to be the most efficient approach to manipulate their performance in ultraviolet-to-visible photon conversion. Under UV irradiation, BaSnO exhibited multicolor photoluminescence (MCPL) in the bluish white region. Its origin has not been well studied in the literature and has been probed in this work using synchrotron radiation, positron annihilation and density functional theory. To achieve desirable performance of doped BaSnO in optoelectronics, it is imperative to have correct information on the dopant local site, doping induced defect evolution and efficacy of host to dopant energy transfer (HDET). Extended X-ray absorption fine structure (EXAFS) showed that Eu ions stabilize at both Ba and Sn sites consistent with the highly negative formation energy of around -6.26 eV. Eu doping leads to an intense D→F orange emission and a feeble D→F red emission and an internal quantum yield (IQY) of ∼21% mediated by ET from the defect level of Eu and Eu sites to the valence band maximum (VBM). X-ray absorption near edge structure (XANES) ruled out any role of Sn in the PL of BaSnO or Eu in the PL of BaSnO3:Eu. Interestingly, when co-doped, Eu stabilizes at Sn sites whereas La stabilizes at Ba sites with a formation energy value of -6.44 eV. Based on the asymmetry ratio in emission spectra, it was found that La ions lead to lowering of symmetry around Eu due to increased vacancies and structural distortions, and also suppress the luminescence IQY. We have performed experimental positron annihilation lifetime spectroscopy (PALS) to probe the defects in BaSnO in pristine samples and on doping/co-doping. The positron lifetimes for saturation trapping of positrons in various kinds of defects envisaged in BaSnO and in the defect free system were calculated using the MIKA Doppler program. Such deep insight into the effect of local structures, dopant sites, defect evolution, ET, etc. on the optical properties of BaSnO is expected to provide very deep insight for material scientists into the fabrication of perovskite-based optoelectronic and light-emitting devices.
人们发现，钙钛矿中的缺陷工程是操纵其在紫外到可见光光子转换中性能的最有效方法。在紫外光照射下，BaSnO在蓝白色区域表现出多色光致发光（MCPL）。其起源在文献中尚未得到充分研究，本工作使用同步辐射、正电子湮没和密度泛函理论对其进行了探究。为了使掺杂的BaSnO在光电子学中具有理想的性能，必须掌握有关掺杂剂局部位置、掺杂引起的缺陷演变以及主体对掺杂剂能量转移（HDET）效率的正确信息。扩展X射线吸收精细结构（EXAFS）表明，Eu离子在Ba和Sn位置均稳定，这与约-6.26 eV的高负形成能一致。Eu掺杂导致强烈的D→F橙色发射和微弱的D→F红色发射，以及约21%的内部量子产率（IQY），这是由从Eu和Eu位置的缺陷能级到价带最大值（VBM）的能量转移（ET）介导的。X射线吸收近边结构（XANES）排除了Sn在BaSnO的光致发光或Eu在BaSnO3:Eu的光致发光中的任何作用。有趣的是，当共掺杂时，Eu在Sn位置稳定，而La在Ba位置稳定，形成能值为-6.44 eV。基于发射光谱中的不对称比，发现La离子由于空位增加和结构畸变导致Eu周围对称性降低，并且还抑制了发光IQY。我们进行了实验性正电子湮没寿命谱（PALS），以探测原始样品以及掺杂/共掺杂的BaSnO中的缺陷。使用MIKA多普勒程序计算了BaSnO中设想的各种缺陷以及无缺陷系统中正电子饱和俘获的正电子寿命。对局部结构、掺杂剂位置、缺陷演变、ET等对BaSnO光学性质的影响的这种深入了解，有望为材料科学家深入了解基于钙钛矿的光电子和发光器件的制造提供深刻见解。
