Synthesis,Optical Properties And Application Of Rare Earth Doped Oxide Up/Down Conversion Luminescent Materials

In recent years,the inorganic rare-earth micro/nano-luminescent materials have been widely used in many fields,such as display,illumination,biological imaging because of the unique properties:long lifetime,rich energy level structure,narrow emission band width,wide range of emission wavelength and so on.The oxides in rare-earth doped hosts have become hot spot due to the advantages of simple preparation method and good stability.The preparation methods of oxides are various.The wet chemical method?that is,reaction in solvent?has many advantages,such as uniform samples,low synthesis temperature,controllable size morphology of samples and so on.The wet chemical method will be used to prepare the sample in this work.The fluorescence intensity ratio of thermally coupled states of the rare-earth ion is a non-contact temperature measuring method.Due to the high temperature resistance and sensitivity,great development has been made in the up-conversion luminescent materials.In this work,not only the fluorescence intensity ratio based on the thermally coupled state is studied,but also the fluorescence intensity ratio based on the non-thermally coupled state and excitation intensity ratio are studied.In addition,the rare-earth luminescent materials have potential application in other fields due to the special emission properties.For example,the emissions from rare earth ions located at the bio-optical window can penetrate the deep biological tissue for real-time biological imaging;the rare earth doped phosphors are also commonly used in the industry to prepare LED lamps,the Eu³⁺-doped red phosphors are used to regulate the color temperature of the white LED;The rare-earth trichromatic phosphors are used to produce the compact fluorescent lamp.Other potential applications of rare earth oxides will be further studied in this work,the specific contents include the following aspects:?1?NaYb?MoO₄?₂:Er³⁺/Tm³⁺/Ho³⁺up-conversion phosphors were synthesized by hydrothermal method.By adjusting the pH and the raw materials,the size and morphology of the samples were controlled.Under the excitation of 980 nm,the samples doped with different rare earth ions emitted different characteristic emissions(Er³⁺:528 nm ²H_11/2?⁴I_15/2,550 nm ⁴S_3/2?⁴I_15/2,663 nm ⁴F_9/2?⁴I_15/2;Tm³⁺:477 nm¹G₄?³H₆,649 nm ¹G₄?³F₄;Ho³⁺:544 nm ⁵F₄/⁵S₂?⁵I₈,654 nm ⁵F₅?⁵I₈).The possible up-conversion luminescence mechanism was determined by means of the energy level diagram of rare earth ions and the dependence of emission intensity with pump power.The spectra from 323 K to 573 K were measured.The fluorescence intensity ratios of thermally coupled states(Er³⁺:²H_11/2,⁴S_3/2?⁴I_15/2,Tm³⁺:¹G_4?1?,?2??³H₆,Ho³⁺:⁵F_5?1?,?2??⁵I₈)and non-thermally coupled states(Ho³⁺:⁵F₄/⁵S₂,⁵F₅?⁵I₈)were used for temperature sensing and the sensitivity was also calculated.?2?NaYb?MoO₄?₂:Eu³⁺red phosphor was synthesized by hydrothermal method.The XRD,excitation spectra,emission spectra and CIE coordinates were characterized.The thermal stability at high temperature and the corresponding excitation intensity ratio of MoO₄^2-?337-357 nm?and Eu³⁺?390-405 nm?were obtained to realize the temperature sensing,reaching the maximum sensitivity of0.01136 K^-11 at 498 K.The strong emission peaked in 615 nm of Eu³⁺matches the absorption spectrum of phytochrome P_R in plants.Therefore,the LED devices prepared by the combination of the phosphor and commercial blue chips have potential application in plant growth.?3?YAG:Yb³⁺,Er³⁺,Ho³⁺,Cr³⁺phosphors were synthesized by sol-gel method and characterized by XRD.At the 980 nm excitation,the emission spectra of YAG:Yb³⁺,Er³⁺,Ho³⁺,Cr³⁺sample were obtained.There is no obvious thermal quenching in the emission intensity with heating,and the possible energy transfer mechanism is put forward.The maximum sensitivity of 0.0021 K^-11 at 323 K is obtained when the temperature is sensed by the thermally coupled states splitting from the state of Er³⁺:⁴I_13/2.