Research On Phosphor With Blue,Red And Near Infrared Emissions Used For Plant Growth LED

The indoor farming in greenhouses and controlled-environment closed plant production systems has received more attention due to unpredictable climatic changes and threats such as pests.Light is essential energy source in regulating plant growth and development,supplemental artificial lighting is often necessary in greenhouses to make up for the deficits of natural light.Traditional light sources used in the plant facility cultivation not only mismatch with photosynthetic action spectra,but also consume more energy or threat to environments.Phosphor-converted light-emitting diodes?pc-LEDs?,as a typical energy-saving,high efficiency and environmental-friendly illuminating sources,are considered to be the most preferable light source because its spectral composition can be adjusted according to the needs of plant growth.Therefore,it is necessary to develop multicolor-emitting phosphors for pc-LEDs.In this paper,some phosphors suitable for plant growth LED were prepared using solid state method through chosing the fluorophosphate,orthosilicate and titanate as matrix material,the rare earth ions(Ce³⁺,Eu²⁺,Pr³⁺,Yb³⁺)and transition metal ions(Mn²⁺,Mn⁴⁺)as dopants.Under near-ultraviolet?n-UV?light irradiation,the Ba₃LaNa?PO₄?₃F:Eu²⁺ Pr³⁺phosphors emit blue,red and near-infrared?NIR?light,which match well with the absorption spectra of photosynthetic pigments?chlorophylls,carotenoids and bacteriochlorophyll?.The ratio of red/blue/NIR could be tuned by adjusting the concentrations of Eu²⁺ and Pr³⁺,in which the energy transfer?ET?between Eu²⁺ and Pr³⁺ ions is confirfirmed on the basis of PL spectra and decay curves of the phosphors.Red and blue double-color emitssion could also be realized by singly doping Eu²⁺ and co-doping Eu²⁺-Mn²⁺ in Ba₃LnNa?PO₄?₃F?Ln=Gd,Y?,suggesting its potential application in plant growth white LEDs.The detailed crystal structure,optimal Eu²⁺dopant concertrations and the concentration quenching mechanisms were determined in Eu²⁺-doped Ba₃LnNa?PO₄?₃F?Ln=Gd,Y?.The photoluminescence emission?PL?,excitation?PLE?spectra and decay times at liquid helium temperature were used to identify that Eu²⁺ enter three Ba²⁺ sites.Temperature-dependent PL spectra were used to investigate the site-dependent thermal stability of Eu²⁺,and their luminescence quenching mechanisms were also discussed.The PL and PLE as well as the decay curves of Eu²⁺/Mn²⁺ co-doped Ba₃LnNa?PO₄?₃F?Ln=Gd,Y?phosphors were also investigated,suggesting the occurrence of Eu²⁺?Mn²⁺energy transfer process and the enhancement of greem emission form Mn²⁺.Furthermore,the white LED devices have also been fabricated by combining a 365 nm n-UV LED chip with Ba₃LnNa?P04?₃F:Eu²⁺?Ln=Gd,Y?and Ba₃LnNa?P04?₃F:Eu²⁺,Mn²⁺?Ln=Gd,Y?phosphors.Results indicate that white LED device fabricated with Ba₃LnNa?PO₄?₃F:Eu²⁺,Mn²⁺?Ln=Gd,Y?phosphor exhibits better performance than that with Ba₃LnNa?PO₄?₃F:Eu²⁺?Ln=Gd,Y?phosphors.Tunable blue-green emitting phosphor Ca₂SiO₄:Ce³⁺,Eu²⁺,blue-NIR emitting phosphor Ca1.7Sr0.3SiO₄:Ce³⁺,Yb³⁺ and blue-red-NIR emitting phosphor Li2SrSiO₄:Ce³⁺,Pr³⁺ phosphor show strong broadband absorption in n-UV area,and their emissions can be absorbed by photosynthetic pigments such as chlorophylls,carotenoids and bacteriochlorophyll.The structure and phase,concentration-dependent luminescent properties,the crystallographic occupany of Ce³⁺,thermal stability,the energy transfer processes and efficiencies of Ce³⁺?Eu²⁺/Yb³⁺/Pr³⁺ of mentioned phosphors were investiganted in detail.Mn⁴⁺ ions doped Gd₂ZnTiO₆ phosphor exhibits broad excitation bands in n-UV and blue light region and deep red emission centered at 704 nm.Concentration-dependent luminescent properties and thermal stability of the phosphor were emphatically analyzed.Gd₂ZnTiO₆:Mn⁴⁺,Yb³⁺ phosphor offers deep red emission from Mn⁴⁺ ions as well as NIR emission from Yb³⁺ through efficient energy transfer Mn⁴⁺?Yb³⁺,in which the emiss:ion spectra could better overlap with the absorption spectra of phytochrome and bacteriochlorin,implying that the present phosphor could be used to modulate plant growth by fabricating LED lighting.