Preparation And Properties Of Pr³⁺-doped Deep Ultraviolet Persistent Phosphors

In recent years,visible and infrared persistent phosphors h ave gained considerable attention and are widely used in night vision surveillance,medical diagnosis,optical information storage,optical anti-counterfeiting and other important fields.In contrast,the progress in persistent phosphors emitting at the other end of the spectrum,i.e.,the shorter-wavelength UVC(200-280 nm)and UVB(280-320 nm),is relatively slow,though the growing demand for current practical applications.At present,most of the available UVB and UVC phosphors are photoluminescent,for which continuous external excitation is essential.This luminescence form hinders the further development and application of deep UV luminescence technology.To solve these problems,a series of persistent luminescence materials(Pr3+ as luminescence centers,Lu2SiO5 and garnet as hosts)that can generate deep UV afterglow were designed and synthesized by the sol-gel method and high-temperature solid-state method.The afterglow performance,photostimulated persistent luminescence performance,and persistent luminescence mechanism were studied,and the main contents and results are as follows:(1)The UVC long persistent phosphor,Lu2SiO5:Pr3+,was successfully prepared by the sol-gel method,which can show intense UVC afterglow peaking at 270 nm and a long afterglow duration of more than 12 h after being excited by 254 nm UV lamp.In addition,the UVC persistent luminescence of pre-irradiated samples can be repeatedly enhanced after short-time irradiation with low-energy white light,which is called photostimulated persistent luminescence.Besides,the trap properties of the phosphor including trap depth,trap distribution,and trap density were systematically studied by the thermoluminescence analysis.Owing to the features of UVC light that cannot be interfered by the ambient light and the long-lasting luminescence properties of the phosphor,the UVC afterglow of Lu2SiO5:Pr3+phosphor can be clearly monitored and imaged with a commercial corona camera in bright environments including sunlight and indoor light.The Lu2SiO5:Pr3+ persistent phosphor is expected to find potential applications in the field of convert optical positioning and tagging.(2)A series of Pr3+ doped garnet based UVB long persistent phosphors(Lu,Gd,Y)3(Al,Ga)5O12:Pr3+,Cr3+were designed and developed by combining conduction band engineering,vacuum referred binding energy(VRBE)diagram,co-doping,and persistent energy transfer control.These phosphors can produce prolonged UVB afterglow for more than 60 hours after being charged by a standard 254 nm UV lamp.In addition to the UV lamp,the sample can also be charged by sunlight,which has been proved that the UVA component in sunlight mainly plays the role of filling traps.Besides,the persistent luminescence properties and trap charging and detrapping processes were comprehensively studied by persistent excitation spectra and thermoluminescence experiments to reveal the possible luminescence mechanism in these phosphors.Finally,the unique UVB afterglow of these garnet phosphors can be clearly imaged and recorded by a UVB camera in bright indoor lighting environment due to the zero-background interference of indoor ambient light.