Preparation And Luminescence Properties Of CaYAlO₄ Phosphors Doped With Ti⁴⁺ And Mn⁴⁺

Light is one of the indispensable environmental factors for plant growth and development,far-red light（690-750nm）and blue-violet light（350-460nm）have important effects on flowering,stem elongation and bud formation.It is an important technology in the field of facility cultivation to control plant morphology through light quality regulation.Compared with traditional light source,the LED lamp of new lighting device has advantages of high efficiency,energy saving and long life.Phosphor plays a key role in the process of LED light conversion,which determines the performance such as luminous efficiency,color rendering index and lifetime of the device.Therefore,the preparation of high performance far-red and blue-violet phosphors can significantly improve the efficiency of LED plant growth lights.In this study,CaYAlO₄is used as the matrix material,and Ti⁴⁺and Mn⁴⁺are used as activators,which are blue violet light and far red light respectively.The effects of cation vacancy,solid solution effect and co-mixed flux on luminescence efficiency and thermal stability of phosphors are systematically studied.The specific work is as follows:（1）In this work,CaYAlO₄（CYAO）phosphors activated by Ti⁴⁺ions were synthesized by traditional high temperature solid phase reaction.CYAO:Ti⁴⁺is a new type of phosphor,which emits blue violet light in the range of 350-420 nm under the excitation of 246 nm.The phase purity and morphological characteristics structure of CYAO:Ti⁴⁺phosphor were determined by X-ray diffractometer and electron scanning electron microscope.The Ti⁴⁺occupying Al³⁺site was determined due to the crystal structure and ionic radius analysis of the matrix.The luminescence efficiency of CYAO:Ti⁴⁺phosphor was optimized by Ca vacancy defect,which increased by 26%.The thermal stability of the phosphor was tested.When heated to 150℃,the luminescence intensity remained about 91%of that at room temperature.（2）CaYAlO₄:x Mn⁴⁺,m Sr²⁺,M⁺（M⁺=Li⁺,Na⁺,and K⁺）（CYAO:Mn,Sr,M）series phosphors were prepared by cationic co-doping and their luminescence properties were studied.With the increase of Mn⁴⁺concentration,the luminescence intensity of the two excitation bands（Band A and band B）of the phosphor changed differently,in which the red shift of band A occurred at 18 nm while the band B did not move significantly.The results show that the partial substitution of Sr²⁺for Ca²⁺can improve the luminescence intensity and thermal stability of phosphors.The luminescence mechanism of co-doped monovalent alkali metal ions（Li⁺,Na⁺,and K⁺）was studied.Due to the effect of charge compensation and the increase of the number of Mn⁴⁺luminescence centers,luminescence performance of CSYAO:Mn was improved,and it was concluded that the optimal doping amount（0.6mol%Na）could increase the luminescence intensity of phosphors by 17%.The encapsulated pc-LED device is applied to the growth of tomato seedlings.According to the tested agronomic properties and pigment content,the phosphor is more conducive to the growth of tomato seedlings than other light sources.In summary,using transition metal ion Ti⁴⁺and Mn⁴⁺to activate CaYAlO₄,blue-violet and far-red luminescent materials with good luminescence performance can be obtained.Cationic vacancy,solid solution effect and flux co-mixing can improve the quantum efficiency and thermal stability of phosphors.The phosphor encapsulated LED plant growth lamp can be used in indoor plant cultivation.