Multicolor persistent luminescence realized by persistent color conversion

Abstract

Spectral tuning is important for the development of persistent phosphors. Here we introduce a color conversion concept to obtain abundant persistent luminescence spectra in addition to existing methods of exploring new matrix and/or dopants. In this study, CaAl₂O₄:Eu,Nd was chosen as a blue persistent donor phosphor, while Lu₃Al₅O₁₂:Ce and other four commercial phosphors were explored as conversion phosphors to obtain colorful persistent luminescence spectra. Both the persistent donor phosphor and conversion phosphors were embedded into resin, forming ternary composite chips to ensure efficient energy transfer. Continuous color tuning were realized by simply changing the mass ratio of the persistent donor phosphor vs. conversion phosphor. Our work will be significant in indicating other persistent/conversion composite materials or nanostructures with abundant spectral properties.

Introduction

The emission of persistent phosphors can persist for a long time after the cessation of excitation. Persistent luminescence and persistent phosphors are arousing increasing interests and have found abundant applications in night vision materials, security signals, art painting, mechanical stress detection, high energy particle detection, optical information storage, catalysis, analysis, time-resolved bioimaging, etc [1], [2], [3]. Apparently, these applications rely on the synthesis of persistent phosphors with abundant spectral properties. Many new phosphors have been reported, usually by developing new matrix and/or new dopants. For example, Ca_0.2Mg_0.9Zn_0.9Si₂O₆:Eu,Dy,Mn is the first developed persistent phosphor in persistent luminescence imaging [4], [5]. Cr-doped gallium oxide related phosphors represents the current dominating ones [6], [7], [8], [9], [10], [11], [12]. Novel Cr/Ga-free persistent phosphors are being explored such as Zn₃Ga₂Ge₂O₁₀:Ni²⁺ [13], LaAlO₃:Mn⁴⁺,Ge⁴⁺ [14], BaZrSi₃O₉:Eu²⁺, Pr³⁺ [15], KGaGeO₄:Bi³⁺ [16], semiconducting polymer [17], metal organic framework [18], etc. Although a number of new persistent phosphors have been explored, to date, CaAl₂O₄:Eu,Nd (blue, CAO) and SrAl₂O₄:Eu,Dy (green) still represents the most efficient commercial ones [19], [20].

Regarding spectral tuning, in addition to explore new matrix or dopants, a color conversion strategy has been widely applied in the field of LED lighting to obtain white light [21]. Generally, a blue semiconductor lighting chip and color conversion phosphors are mixed together. Then, conversion phosphors absorb part of the blue light and emit green, yellow and/or red light to generate abundant visible colors based on the trichromatic theory [22], [23], [24], [25], [26]. Inspired by these works in LED color tuning, we propose that multicolor persistent spectral tuning can also be realized by color conversion. Here, CAO is chosen as a persistent donor as it is currently the most efficient blue persistent phosphor [19]. Ce³⁺-doped lutetium aluminum garnet (Lu₃Al₅O₁₂:Ce³⁺, LuAG), which is one of the most efficient green color conversion phosphors in LED industry, is used as a color conversion phosphor [27], [28], [29]. We try to tune the blue persistent luminescence by changing the mass ratio of LuAG in CAO/LuAG composite. This color conversion strategy was further explored by using four other conversion phosphors to generate abundant persistent color.