Glow-in-the-Daylight Phenomenon And The Luminescence Spectroscopy Of Persistent Phosphors

Persistent luminescence is a phenomenon that phosphors continue to emit light after ceasing the excitation.Common persistent luminescence applications are in dark environment,such as night-vision tracking,anti-counterfeiting and bioimaging probes.Therefore,dark environment is often considered to be a prerequisite for persistent luminescence.Such an empirical viewpoint has hindered the application and development of persistent phosphors in lighting environment.If persistent luminescence can be detected in lighting environment,it will provide a novel concept and technical option for all-weather optical tracking.According to the luminescence mechanism of persistent phosphor,persistent luminescence does not only occur in dark environment.The detection of persistent luminescence in lighting environment should avoid the spectral overlap between the emission of persistent phosphor and ambient light.Obviously,ultraviolet persistent phosphors with visible blind emission provide a choice for achieving glow-in-the-daylight emission.In this paper,the spectroscopic investigations of glow-in-the-daylight are carried out on several typical ultraviolet persistent phosphors and up-conversion charging persistent phosphors.The study of ambient light stimulation spectroscopy and excitation spectroscopy reveals the influence of ambient light and excitation light properties on glow-in-the-daylight emission process.The specific research contents are as follows:（1）The concept of glow-in-the-daylight of persistent phosphors is introduced,which is defined as the persistent luminescence that can be detected in ambient lighting environments.This concept takes into account the effect of ambient lighting stimulation into the mechanism framework of persistent luminescence.Taking LuPO₄:Pr³⁺phosphor as an example,its glow-in-the-daylight emission under sunlight is observed by imaging demonstration.And the variation of glow-in-the-daylight emission intensity with time is obtained by spectral measurement.Thermoluminescence experiment reveals the relationship between the glow-in-the-daylight emission and the sunlight stimulation.The introduction of glow-in-the-daylight emission expands the application range of persistent phosphors,so that it can be used for tracking and anti-counterfeiting in ambient lighting environments.（2）The effect of ambient light stimulation on the glow-in-the-daylight emission process is investigated using LaMgAl₁₁O₁₉:Gd³⁺phosphor as an example.Spectral measurements indicate that the release of stored energy is caused by both ambient temperature stimulation and ambient lighting stimulation.Thermoluminescence experiments are designed to confirm that the contribution of ambient temperature stimulation and ambient lighting stimulation to the glow-in-the-daylight emission is comparable.The influence of the ambient light illuminance and spectral distribution on glow-in-the-daylight emission intensity is explored,and glow-in-the-daylight emission is extended to various phosphors to prove its universality.This work contributes to the further understanding of glow-in-the-daylight emission process and influencing factors.（3）The up-conversion charging excitation approach of persistent phosphor is explored and the physical process of up-conversion charging is regulated.Taking YBO₃:Pr³⁺phosphor as an example,it can exhibit ultraviolet emission under blue laser excitation.The two-photon excitation process and excited state absorption up-conversion mechanism is verified by spectral measurements.On the basis of up-conversion luminescence spectroscopy,LaMgGa₁₁O₁₉:Pr³⁺phosphor is selected to investigate the up-conversion charging dynamics.The up-conversion charging induced persistent luminescence under blue light excitation is realized in LaMgGa₁₁O₁₉:Pr³⁺phosphor.By constructing and analyzing the up-conversion charging dynamic model and combining with experiments,the competitive relationship between trapping and detrapping is explored.The result shows that the competitive relationship depends both on the illumination power and on the illumination duration.This work contributes to the further understanding of up-conversion charging,and also paves the way toward expanding the excitation approach of glow-in-the-daylight emission.（4）The up-conversion charging induced glow-in-the-daylight emission is designed by combining glow-in-the-daylight concept with up-conversion charging approach.The ultraviolet glow-in-the-daylight emission under blue laser excitation is realized in Lu₃Al₂Ga₃O₁₂:Pr³⁺,Gd³⁺phosphor.The two-photon excitation process is verified by measuring glow-in-the-daylight emission spectra under different excitation conditions.By measuring the spectra of the phosphor irradiated with different light sources,it is shown that the excitation mechanism of up-conversion charging is excited state absorption up-conversion.The influence of the ambient light illuminance and spectral distribution on up-conversion charging induced glow-in-the-daylight emission intensity is investigated by spectral measurements.The glow-in-the-daylight emission of the phosphor is expanded by charging with a white light flashlight.In addition,the imaging demonstration indicates the potential of up-conversion charging induced glow-in-the-daylight emission as an anti-counterfeiting mark in ambient lighting environments.