Preparation And Property Tuning Of Several Typical Oxide-based Broadband Luminescent Materials

With the emergence of high-brightness blue InGaN LEDs,white LEDs,as a new solid-state illumination source,have made remarkable progress and have integrated into people's daily lives due to their many advantages such as energy saving,environmental protection,and portability.Therefore,various types of phosphors with outstanding performance are constantly researched,developed and utilized with the development of LED chip technology.Aiming at the characteristic peak linear emission due to the f-f transition of most trivalent rare-earth ion-activated luminescent materials,and the key issues of low luminous efficiency and narrow spectral absorption range,this thesis selects Eu²⁺based on d-f allowed transition and Bi³⁺based on s-p allowed transition as activators,explores several oxide luminescent materials with broadband emission properties that make the human eye comfortable,and studies the relationship between matrix structure and luminescence performance.The main research contents are as follows:1.A new type of zirconium-containing silicate luminescent material K₂ZrSi₂O₇:Eu²⁺was prepared by the solid-state reaction method,and its crystal structure was determined from the XRD Rietveld refinement and high-resolution transmission electron microscope data.Excited by?n?-UV light,K₂ZrSi₂O₇:Eu²⁺emits bright blue light with a peak of 462 nm and a full width at half maximum of 70 nm.Under continuous low-voltage electron bombardment,the luminescent material displays excellent degradation resistance and good color stability.Solid solution K₂Zr/HfSi₂O₇:Eu²⁺can be formed by gradually replacing Zr⁴⁺in the system with Hf⁴⁺,and the thermal stability of this solid solution improved significantly with the increase of the substitution amount of Hf⁴⁺.2.Inspired by the above-mentioned solid solution,a dipotassium hafnium trisilicate K₂HfSi₃O₉ with wadeite structure was synthesized.Its detailed crystal structure and electronic structure were determined using XRD data and density functional theory?DFT?,respectively.Steady-state photoluminescence spectra and time-resolved spectra indicate that there are two types of Eu²⁺luminescence centers in K₂HfSi₃O₉:Eu²⁺.Based on the crystal-site engineering method,replacing Hf⁴⁺with trivalent ion Sc³⁺in the matrix can improve the absorption of Eu²⁺in the blue light spectral region,and can also tuning the position and shape of the emission spectrum,and effectively improve the luminous thermal quenching performance.With increasing the substitution amount of Sc³⁺ions,the emission spectrum of this system shifted from 462 nm to 507 nm.When the ambient temperature is as high as 200 ?,the emission loss of the sample is almost zero,which is better than commercial phosphors such as BAM:Eu²⁺and Sr₃SiO₅:Eu²⁺.The thermoluminescence spectrum and temperature-dependent decay curves show that the robust thermal quenching of the sample may be related to the energy transfer from the defect levels to the vicinity of Eu²⁺5d band.3.BaZrSi₃O₉:Bi³⁺,A yellow luminescent material,was prepared in a high-temperature box furnace using Bi³⁺as an activator.Its phase structure,luminescence properties,and decay curves were studied in detail.Under?n?-UV excitation,BaZrSi₃O₉:Bi³⁺emits yellow light with a full width at half maximum of 125 nm and a main peak at 560 nm.The broad emission band is originated from ³P₁?1?¹S₀ transition of Bi³⁺,which has a lifetime around 0.9?s in BaZrSi₃O₉.The emission intensity of BaZrSi₃O₉:Bi³⁺at 150 ? is 76%of that at room temperature,which is comparable to that of commercial YAG:Ce³⁺phosphor.The blue shift of the emission spectrum with increasing temperature involves thermally activated phonon-assisted tunneling.4.Using borate material Ba₃ScB₃O₉ as matrix and Eu²⁺as activator,an ultra-broadband near-infrared luminescent material was designed and prepared by solid-state reaction method under a certain pressure in a high-purity nitrogen atmosphere.The relationship between the crystal structure and luminescence properties of Ba₃ScB₃O₉:Eu²⁺has been studied in detail.Ba₃ScB₃O₉:Eu²⁺,in response to UV-blue light excitation,yields visible-near infrared light with the main peak,full width at half maximum and Stokes shift of 735 nm,205 nm and 12991 cm^-1,respectively.The spectral position,bandwidth and Stokes shift can be rationalized by combining the nephelauxetic effect and crystal field theory.The blue shift of the emission spectrum can be achieved by replacing Ba²⁺with Sr²⁺in the matrix.By covering this phosphor on a blue LED chip?450 nm?,a good VIS-NIR pc-LED device has been obtained.