Structure, long persistent luminescent properties and mechanism of a novel efficient red emitting Ca2Ga2GeO7:Pr3+ phosphor

Abstract

A novel red emitting long persistent luminescent phosphor Ca 2 Ga 2 GeO 7 :Pr 3+ (2217) was developed by solid state method at 1300 °C in air. The refined crystal structure of Ca 2 Ga 2 GeO 7 host was solved. The intense red long persistent luminescence originates from the f-f transitions of Pr 3+ centers at highly disordered Ca 2+ sites in CaO 8 polyhedrons. It can be properly recorded for 1.5 h by the definition of 0.32 mcd/m 2 and is actually visible for more than 5 h by dark-adapted vision in darkness. At least one type of intrinsic lattice defects of the Ca 2 Ga 2 GeO 7 host as proper shallow traps exists in Ca 2 Ga 2 GeO 7 :Pr 3+ material and the depth of the traps is calculated to be 0.59 eV, which is very suitable for long persistent luminescence. It reveals that the Pr 3+ dopants not only act as emitters but also increase the density of these significant intrinsic traps, resulting in the efficient persistent luminescence of Pr 3+. The

B-site mixed cationic tetrahedral layer confined the concentration and mobility of interstitial oxygen in mellite family

“…2e–h. The cRED data can be indexed directly into a tetragonal unit cell: a = b = 7.9933 Å; c = 5.3504 Å, α = β = γ = 90°, which is in good agreement with the parent structure of Ca 2 Ga 2 GeO 7 , 19 thus ruling out the possibility of structural transition upon the La doping on the Ca site. SEM images of Ca 2− x La x Ga 2 GeO 7+ x /2 ( x = 0, 0.05, 0.1 and 0.15) samples show an evident sheet-like morphology (Fig.…”

“…+2/+5 in K 2 ZnV 2 O 7 , 17 +2/+4 in Ca 2 MgSi 2 O 7 (ref. 18) and +3/+4 in Ca 2 Ga 2 GeO 7 , 19 where the divalent cations of Zn/Mg usually sit in B′ sites. So far, interstitial oxide ion conduction in melilites was observed only in pure gallate or aluminate compositions, where the aluminate compounds are metastable and exhibit lower oxide ion mobility than the gallate compounds.…”

Oxygen Vacancy Migration in Ca2Ga2+xGe1–xO7–0.5x Melilite

“…The structure of Ca 2 Ga 2 GeO 7 was determined previously by Wang et al using X-ray diffraction, isostructural with Ca 2 MgSi 2 O 7 , showing partially ordering of Ga and Ge at the 2a and 4e sites, where the 2a site is exclusively occupied by Ga1 and the 4e site is occupied by Ga2 and Ge1. The adjacent Ga and Ge elements are difficult to discern by XRD.…”

“…The structure of Ca 2 Ga 2 GeO 7 was determined previously by Wang et al using X-ray diffraction,46 isostructural with Ca 2 MgSi 2 O 7 ,…”

Recent advances in Pr3+-activated persistent phosphors

“…For example, in alkaline earth metal compounds, Pr 3+ is likely to occupy the sites belonging to alkaline earth metal ions (A = Ca 2+ , Sr 2+ , Mg 2+ , etc. ); 12,40,[56][57][58][59][60][61][77][78][79]95,97,100 in alkali metal compounds Pr 3+ takes sites of alkali metal ions (B = Li + , Na + , Cs + , etc.). 40,41,54,67,84,98,131 The charge imbalance caused by Pr 3+ heterovalent substitution is believed to provide appropriate electron trapping centers surrounding Pr 3+ (Pr A or Pr B ).…”