The Construction And Energy Transfer Of Manganese (IV) And Rare Earth Ions Co-activated Double-layer Perovskite Luminescent Materials

Rare earth?RE?and transition metal ions doped luminescent materials have been widely applied in the fields of lightings,displays,lasers,optical amplifiers for telecommunication,spectral converters for solar cell,and biological fluorescent probes,owing to their unique and superior luminescent properties.In these applications,energy transfer process plays an important role in the performance of luminescence materials.Mutual energy transfer between rare earth ions and transition metal ions in a single luminescence material is to easily achieve multifunction by altering excitation wavelength.In this paper,double perovskite RE₂ZnTiO₆phosphors co-doped with different trivalent rare-earth ions and tetravalent manganese ions were synthesized by different methods.Utilize Mn⁴⁺ion effective energy transfer to rare earth ions or rare earth ions energy transfer to Mn⁴⁺ions,thereby realizing characteristic emission of rare earth ions or Mn⁴⁺ions,and then applied to near-infrared solar cells,solid-state lasers,anti-counterfeiting and warm white LEDs.In addition,the energy transfer mechanism in the Mn⁴⁺/RE³⁺co-doped RE₂ZnTiO₆ single-matrix material was revealed by the study of spectral properties and fluorescence dynamics.We first observe the mutual energy transfer process between Mn⁴⁺and Er³⁺via different excitation in Mn⁴⁺-Er³⁺co-doped Gd₂ZnTiO₆ phosphors synthesized by a high temperature solid-state reaction.During the downshift energy transfer from Mn⁴⁺to Er³⁺,the Gd₂ZnTiO₆:Mn⁴⁺/Er³⁺phosphor exhibits a strong near-infrared emission around 1529 nm with a wide excitation band extending from 250 to 550 nm.Based on Dexter's theory,the energy transfer mechanism is mainly contributed to a dipole-dipole interaction between Mn⁴⁺and Er³⁺ions,which is responsible for the largely enhanced emission at 1529 nm.Upon the upconversion energy transfer from Er³⁺to Mn⁴⁺,the Gd₂ZnTiO₆:Mn⁴⁺/Er³⁺phosphor shows a deep red emission of Mn⁴⁺under 980 nm laser excitation.The energy transfer process from Er³⁺to Mn⁴⁺is fully demonstrated by the variations of excitation power as well as luminescence lifetimes of 551 nm emission of Er³⁺.Two-photon processes and resonance energy transfer from Er³⁺to Mn⁴⁺are required to populate the²E emitting level of Mn⁴⁺.The Mn⁴⁺/Yb³⁺co-doped La₂ZnTiO₆(brief as LZT:Mn⁴⁺/Yb³⁺)phosphors with xYb³⁺?x=0-0.12?and yMn⁴⁺?y=0-0.01?doping concentrations have been prepared by a sol-gel method.X-ray diffraction?XRD?and photoluminescence spectra were used to characterize the properties of LZT:Mn⁴⁺/Yb³⁺phosphors.The LZT:Mn⁴⁺/Yb³⁺material can efficiently shift the short-wavelength sunlight in wide spectral regions?250-600 nm?into near infrared emission around 990 nm which matches the higher sensitivity region of Si-based solar cells.A dipole-dipole interaction is responsible for the energy transfer sensitization processes from Mn⁴⁺to Yb³⁺ions,which has been confirmed by Dexter's theory.Under the 390 nm excitation,the energy transfer efficiency is 38.6%in the La_1.9ZnTi_0.998O₆:0.002Mn⁴⁺/0.1Yb³⁺co-doped sample.Due to the effective absorption of Mn⁴⁺in the visible region and charge transfer transitions(Yb³⁺-O^2-and Mn⁴⁺-O^2-)in the UV region in LZT and the efficient energy transfer to Yb³⁺,this material can be potentially applied to spectral convertors to improve silicon solar cell photovoltaic conversion efficiency.Different xDy³⁺?x=0-0.07?single-doped and yMn⁴⁺/0.05Dy³⁺?y=0-0.01?co-doped La_2-xZnTi_1-y-y O₆?LZT?phosphors were prepared by a sol-gel method.Concentration dependence studies have shown that the optimal doping concentration for Dy³⁺single doping is x=0.05.The obtained phosphor can be effectively excited by UV light and exhibits strong blue light?484 nm?,yellow light emission?576 nm?,weak red light?668 nm?and strong crimson light emission?710 nm?,which are assigned to the ⁴F_9/2?⁶H_15/2,⁴F_9/2?⁶H_13/2,⁴F_9/2?⁶H_11/21/2 energy levels transitions of Dy³⁺ions and ²E?⁴A₂ energy levels transitions of Mn⁴⁺ions,respectively.Based on the Dexter theory,it was shown that the energy transfer from Dy³⁺to Mn⁴⁺can be observed in the LZT:Mn⁴⁺/Dy³⁺phosphors and was confirmed as a result of dipole-dipole interactions.By varying the doping concentration ratio of Mn⁴⁺/Dy³⁺,adjusting the emission at different excitation wavelengths can be observed from orange to white to deep red from the color coordinates.The results indicate that La₂ZnTiO₆:Dy³⁺yellow phosphors prepared by sol-gel method can potentially be used for solid state illumination,and La₂ZnTiO₆:Mn⁴⁺red phosphors can potentially be used for solid-state lasers and plant growth illumination,while Mn⁴⁺/Dy³⁺co-doped La₂ZnTiO₆ phosphors can be used for single-phase white LEDs.