The influence of defects formed by Ca excess and thermal post-treatments on the persistent luminescence of CaTiO_3:Pr

Abstract

Red emitting CaTiO 3 :Pr phosphors with a nominal composition of Ca 0.998+x Pr 0.002 TiO 3+δ (0.02≤x≤0.04) were prepared by solid state reactions with different thermal post treatments and characterized by X-ray diffraction, transmission electron microscopy and photoluminescence. The Ca excess exhibited complete solubility up to 4% in the samples treated at 1400 °C but segregation in the form of Ruddlesden-Popper phases (Ca 3 Ti 2 O 7 -Ca 4 Ti 3 O 10 ) was observed in samples prepared at 1500 °C. The increase in temperature for stoichiometric samples showed a monotonic increase of decay time due to the reduction of non-radiative recombination defects. It was found that the Ca excess favored the formation of oxygen vacancies which are known to act as trap. In the samples treated at 1400 °C, 3% of Ca excess showed to be the best concentration to increase the decay time of persistent luminescence. For the samples treated at 1500 °C, the segregation of Ruddlesden-Popper phases left a constant amount of Ca soluble in all the CaTiO 3 samples. This constant concentration of Ca caused the same density of defects and, consequently, the same decay time in all samples. ©2012 Optical Society of America

Increased fluorescence intensity in CaTiO3:Pr3+ phosphor due to NH3 treatment and Nb Co-doping

“…7, where we note that the dominant donor and acceptor defects under oxygen-rich conditions are the titanium-on-calcium antisite at low chemical potential, and cation vacancies (calcium or titanium) at high chemical potential. Although oxygen vacancies have been speculated to be the trap state in other studies [14,15], this result indicates that oxygen vacancies are an unlikely defect and cannot be the trap state for these samples. The trap state in this system is more likely due to cation vacancies and their interaction with surrounding oxygen atoms.…”

“…This suggests that Nb 5+ doping eliminates, or concentrates and immobilizes, oxygen that is interacting with a cation vacancy. We hypothesize that this reduces the quenching effect on the luminescence by eliminating this trap state, which is identified as an oxygen-cation vacancy pair, not an oxygen vacancy as previously hypothesized [14,15]. The NH3 treatment seems to have less of an effect, or perhaps only affects the surface, in healing this trap state.…”

“…There have been a few studies that have attempted to characterize the trapping centers in these materials. One study increased the Ca concentration, which led to an increase in trap states that were presumed to be oxygen vacancies [14]. The energies of these trap states were measured at different sintering temperatures and two traps were identified [15].…”

Sol–Gel Synthesis of CaTiO3:Pr3+ Red Phosphors: Tailoring the Synthetic Parameters for Luminescent and Afterglow Applications

“…Indeed local Ca excesses, such as isolated defects or grouping with irregular periodicity, might not be appreciable from XRPD analyses. 20 …”

Phosphorescence behavior and photoluminescence mechanism of Dy 3+ sensitized β-Zn 3 (PO 4 ) 2 : Mn 2+ phosphor

“…LPP can exhibit variety of colors in the darkness, most especially blue (CaAl 2 O 4 : Eu 2+ , Nd 3+ ) and green (SrAl 2 O 4 : Eu 2+ , Dy 3+ ) [9][10][11]. Although many red LPP materials, such as Y 2 O 2 S: Eu 3+ , Mg 2+ , Ti 4+ [12], Y 2 O 3 : Eu 3+ , Ho 3+ [13], CaTiO 3 : Eu 3+ [14], CaTiO 3 : Pr 3+ [15] and b-Zn 3 (PO 4 ) 2 : Mn 2+ , Sm 3+ [16] have been reported, red LPP materials are still far beyond practical application since their phosphorescence persisting times are very short. According to the trichromatic theory of color vision, the combination of red, green and blue in appropriate intensities can create various colors.…”