Germanium substitution endowing Cr3+-doped zinc aluminate phosphors with bright and super-long near-infrared persistent luminescence

Abstract

We present novel near-infrared (NIR) Cr 3+-doped non-gallate superlong-persistence phosphors (Zn1+xAl2-2xGexO4:Cr 3+) by Germanium substitution in the original ZnAl2O4:Cr 3+. Unlike the negligible NIR persistent luminescence of ZnAl2O4:Cr 3+ upon UV or visible light excitation, the Ge substituted phosphors feature strong and super-long-persistent luminescence at approximately 650-750 nm for more than 120 h. The relation between the Ge substitution and the defect trapping states is investigated systematically. The experimental results combined with the first-principles calculations reveal that Ge ○○ Zn and Ge ○ Al in the spinel structure would introduce shallow and deep defect states in the band gap to serve as new efficient traps, which are mainly responsible for the strong and super-long-persistent luminescence upon UV or visible light excitation. The present advanced phosphors is an alternative candidate for applications in biomedical imaging and night-vision surveillance.

Defect states and kinetic parameter analysis of ZnAl2O4 nanocrystals by X-ray photoelectron spectroscopy and thermoluminescence

“…Oxygen vacancies situated deep in forbidden band gap region are responsible for such NIR emission 6 . These defects are excitation energy dependent, as many researchers have earlier observed different emission spectra on changing excitation energy 6,7,9,10,38,39 . Sample S2 is showing a shift of ~40 nm in NIR peak position as compared to S1.…”

“…Metal oxides are drawing considerable attention owing to their non-toxic nature and tunable luminescence properties attributable to the defect states. Zinc aluminate (ZnAl 2 O 4 ) is a well known member of spinel family possessing versatile properties and magnificent applications [5][6][7][8][9][10] . It crystallizes in fcc crystal system with Fd3m space group.…”

“…Due to complex crystal structure and multiple defect centers such as cationic-anionic vacancies, antisite defects and cationic interstitial, it shows alluring luminescence [6][7][8][9] . Most of the work has been reported on photoluminescence of undoped as well as doped ZnAl 2 O 4 [8][9][10][12][13][14][15][16] . However, in order to understand the defect levels and their nature in a material, it must be studied rigorously, which can be brought about by TL study.…”

Na2TiGeO5—A self‐light‐emitting phosphor with the stable structure and tunable emission resulted from Cr3+‐doped for FEDs

“…Another peak located at 300 nm can be attributed to the 2 T 2 ‐ 2 E transitions of Ti 4+ ions, which has also been found in Na 2 TiSiO 5. With the Cr 3+ ions entering into the host lattice, the extra absorption band peaked at 380 nm, 430 and 500 nm can be detected, which can be attributed to 4 A 2 ‐ 4 T 1 (4P), 4 A 2 ‐ 4 T 2 (4F) and 4 A 2 ‐ 4 T 1 (4F) transitions of Cr 3+ ions, respectively . In contrast to the PLE spectrum of Cr 3+ ‐doped Na 2 TiGeO 5 , only the 500 nm absorption band is corresponding and the 300 nm excitation band is assigned to CTB of Cr 3+ ‐O 2− Moreover, the overlap between emission spectrum of host lattice and absorption band of Na 2 TiGeO 5 : Cr 3+ implies that the energy transfer would happen between the two luminescence centers.…”

Identifying Near‐Infrared Persistent Luminescence in Cr3+‐Doped Magnesium Gallogermanates Featuring Afterglow Emission at Extremely Low Temperature

“…Solid solutions of many compounds with persistent luminescence have been designed, such as Sr 3 Sn 2− x Si x O 7 , Sr 3 Sn 2− x Ge x O 7 , LaAl 1− x Ga x O 3 , La 1− x Gd x AlO 3 , Zn 1+ x Ga 2−2 x Sn x O 4 , Zn 1+ x Ga 2−2 x Ge x O 4 , Zn 1+ x Al 2−2 x Ge x O 4 , ZnGa 2−2 x Al 2 x O 4 , Zn 2− x Al 2 x Sn 1− x O 4 , and so forth . Rational design of solid solutions with continuous composition variations or possible substitutions in different occupation sites requires several criteria: ionic radii, coordinated environment, valance states, and chemical stability .…”