Study On Red Phosphors For LED Plant Growth Lamps

Photosynthesis and light morphology of plants are dependent on the absorption of red light and near infrared light.Excellent red light emission at 600-700 nm promotes the light absorption and light transport of most chlorophyll a and all chlorophyll b molecules,and the photosensitive pigment P_R exhibits an absorption spectrum at 650-750 nm near-infrared light.In order to meet the light requirements of plants in unnatural conditions such as conservatories,growing greenhouses and greenhouses,artificial light sources need to be prepared as supplementary light sources to promote the high speed of indoor growing in agriculture and horticulture.Commonly used traditional plant growth lights are provided by light sources such as incandescent,xenon and high-pressure mercury lamps.In recent years,phosphor-excited light-emitting diodes（Light Emitting Diode,LED）have become an emerging lighting device due to their energy-saving,environmentally friendly,low-cost,long-life,easy-to-adjust spectrum and other advantages.Therefore,the preparation of high performance red phosphors for the preparation of LED plant growth lights is urgently needed.In this paper,a series of highly efficient and novel red phosphors were synthesized by high-temperature solid-phase method using Mn⁴⁺as activator ion,and characterized by X-ray diffraction（XRD）,electron sweeping microscope（SEM）,X-ray energy spectrometer（EDS）,X-ray photoelectron analysis（XPS）,UV-Visible Absorption Spectroscopy（UV-vis）and other characterization methods to investigate in detail the phase structure,morphological characteristics,luminescence properties and other mechanisms of phosphors,In addition,the best phosphors will be packaged into LEDs to demonstrate their practical potential.The main studies are as follows:（1）A high-temperature solid-phase synthesis of the bis-chalcogenide Ca₂Lu Nb O₆:x Mn⁴⁺（x=0.003,0.005,0.01 and 0.015）red phosphor.The Mn⁴⁺-doped Ca₂Lu Nb O₆ phosphor shows two distinct excitation peaks in the 200-600 nm range.The luminescent material emits a deep red light at a wavelength of 684 nm when excited at the optimum excitation position of 352 nm,which clearly overlaps with the typical absorption bands of chlorophyll a and chlorophyll b.The crystal structure was studied finely by powder XRD and Rietveld and the optimum doping content of Mn⁴⁺was discussed.The luminescence mechanism of the phosphor was investigated by Tanabe-Sugano plots and the effects of the electron cloud rearrangement effectβ₁,the crystal field strength D_q and the Racah parameters B and C on the luminescence properties of Mn⁴⁺were discussed in detail.The high-temperature thermal stability of the phosphor was investigated,and the calculated value of the activation energy E_a of Mn⁴⁺ions in Ca₂Lu Nb O₆:Mn⁴⁺phosphor was about 0.283 e V,demonstrating its good thermal stability.Finally,red LED chips were fabricated based on Ca₂Lu Nb O₆:0.005Mn⁴⁺phosphor and 365 nm light emitting diodes.The results show that Ca₂Lu Nb O₆:0.005Mn⁴⁺is a phosphor that can potentially be used for plant cultivation LEDs.（2）Sr₂Lu Nb O₆:x Mn⁴⁺（x=0.005,0.01,0.015 and 0.02）red phosphor was successfully prepared by the high temperature solid phase method.The XRD peaks of the resulting samples were consistent with those of the standard card,indicating that the resulting samples were Sr₂Lu Nb O₆ crystals.The sample emitted a deep red light at688 nm under excitation at 350 nm.The crystal field intensities D_q were calculated from the Tanabe-Sugano energy level mapping with Racah constants B and C of 1969 cm^-1,838 cm^-1 and 2805 cm^-1,respectively.This phosphor has a high activation energy of E_a=0.267 e V from the variable temperature fluorescence spectrum of 303-673 K.The above analysis indicates that Sr₂Lu Nb O₆:x Mn⁴⁺（x=0.005,0.01,0.015 and 0.02）red phosphors are expected to be used in commercial production.（3）A series of Er³⁺,Yb³⁺co-doped AWO₄（A=Ba,Sr and Ca）scheelite phosphors and Er³⁺,Yb³⁺co-doped Mg WO₄ wolframite phosphors have been successfully synthesized by high temperature solid phase method,and the up-conversion（UC）luminescence characteristics of AWO₄（A=Ba,Sr,Ca and Mg）phosphors have been comparatively studied.The up-conversion characteristics of the AWO₄（A=Ba,Sr,Ca and Mg）phosphors were investigated.The Er³⁺,Yb³⁺co-doped Mg WO₄ phosphors showed the best UC emission intensity.The temperature sensing performance of Er³⁺,Yb³⁺co-doped AWO₄（A=Ba,Sr,Ca and Mg）phosphors was investigated.The relative sensitivity（Sr）of the green light(²H_11/2/⁴S_3/2)thermal coupling stages（TCLs）based on Er³⁺ions increased with increasing matrix phonon energy.The absolute sensitivity（Sa）of the samples can be accurately predicted from the chemical bonding parameters.The correlation between UC luminescence properties and microscopic crystal structure,as well as the relationship between temperature sensitivity and matrix parameters,was investigated,which also provides insight into the selection of matrix materials with ideal temperature measurement capabilities.