Preparation And Luminescence Of Oxide-hosted Far-red Emitting Phosphors For Bio-lighting

The generalized bio-lighting technology based on non-human eye visual lighting covers a wide spectrum range from ultra-violet（UV）to far-red（FR）light.With the rapid development of plant factories and vertical farms aiming at green and low-carbon technology,high efficiency and energy-saving,plant artificial radiation light source is required to cover the broad-spectrum range by providing specific photonic energy for plant growth photosynthesis.Due to the limitation of the manufacturing technology of long-wavelength red light-emitting semiconductor chip,the combination of the Al In Ga N blue-violet light chip with the long-wavelength red light convertible phosphor is an important scheme to construct the above artificial plant light source.External fields including microwave（MW）field enable preparation and synthesis of materials to be energy-saving,cleaner and faster,becoming one of important technical routes for the synthesis of fluorescent materials.In this work,three oxide-based,blue/ultraviolet excitable,far-red emitting phosphors with different crystal structures were prepared by microwave firing particularly and high temperature solid state method as well.The main achievements are summarized as follows:A.The microwave firing method was employed to synthesize far-red emitting Zn Ga₂O₄:Cr³⁺phosphor at a relatively lower firing temperature and compared with solid state method.Micrometer-sized phosphor particles with smooth morphology were obtained due to the microwave-induced small temperature gradient between the constituent particles upon the local dielectric volumetric heating.The microwave fired Zn Ga₂O₄:Cr³⁺phosphor exhibited excitable properties at the wavelengths of 260 nm,410 nm and 550 nm,respectively and the emission centers are located at 690 nm and700 nm,respectively.In addition,the intensity of photoluminescence excitation at 260nm showed a dramatic enhancement,most likely due to the fact that"non-thermal effect"of the microwave irradiation leads to the reduction of the defects in Zn Ga₂O₄host.These results together with decay time,thermal quenching and color coordinate evaluations showed that synthesis of far-red emitting Zn Ga₂O₄:Cr³⁺by microwave firing method has advantages of high efficiency,energy saving and least environmental threats.B.A new composition in Sr₃Na Nb O₆:Mn⁴⁺phosphor with far-red emission was synthesized via the high-temperature solid-state reaction method using Sr₃Na Nb O₆as a host.The phase composition and morphological characteristics as well as the photoluminescent properties of Sr₃Na Nb O₆:Mn⁴⁺were investigated and discussed in detail.The space group of Sr₃Na Nb O₆:Mn⁴⁺belongs to R-3c H with the lattice parameters a=b=9.7722（?）,c=11.601（?）.In addition,the particle size of Sr₃Na Nb O₆:Mn⁴⁺can be controlled at the micron level.The photoluminescence excitation and photoluminescence spectra showed that Sr₃Na Nb O₆:Mn⁴⁺phosphor has an emission band centered at 700 nm under the excitation of 370 nm UV light.The emission band in the region of 600-800 nm of Sr₃Na Nb O₆:Mn⁴⁺phosphor covers well with the absorption of red（P_R）and far-red(P_FR)phytochromes.C.The M₃Ga₅O₁₂:Cr³⁺（M=Lu,Y）phosphor was prepared by high temperature solid state method.The crystal structure,UV-vis diffuse reflectance spectra,photoluminescence excitation and emission spectra,thermal stability and CIE chromaticity coordinates of M₃Ga₅O₁₂:Cr³⁺phosphor were investigated.M₃Ga₅O₁₂:Cr³⁺phosphor had the garnet structure.The UV-vis diffuse reflectance spectra with three absorption peaks were consistent with its excitation spectra.The excitation spectra of M₃Ga₅O₁₂:Cr³⁺phosphors cover the band of 200-700 nm,and the emission center is located at～710 nm.The results showed that the spectral characteristics of Lu₃Ga₅O₁₂:Cr³⁺and Y₃Ga₅O₁₂:Cr³⁺exhibit high consistency in between when M was Lu or Y,respectively.The 5 nm shift of emission peaks of Lu₃Ga₅O₁₂:Cr³⁺and Y₃Ga₅O₁₂:Cr³⁺could be ascribed to the radius difference between Lu³⁺and Y³⁺.Furthermore,the luminescence intensity of M₃Ga₅O₁₂:Cr³⁺phosphors can maintain the initial 72.4%/82.1%at 150℃,showing its high thermal stability.The CIE chromaticity coordinates at（0.717,0.283）,（0.713,0.289）are located in the far-red region.