Improved photoluminescence and afterglow of CaTiO_3:Pr^3+ by ammonia treatment

Abstract

Abstract:The phosphor CaTiO 3 :Pr 3+ was synthesized via a solid-state reaction in combination with a subsequent annealing under flowing NH 3 . Comparatively large off-center displacements of Ti in the TiO 6 octahedra were confirmed for as-synthesized CaTiO 3 :Pr 3 by XANES. Raman spectroscopy showed that the local crystal structure becomes highly symmetric when the powders are ammonolyzed at 400 °C. Rietveld refinement of powder X-ray diffraction data revealed that the samples ammonolyzed at 400 °C have the smallest lattice strain and at the same time the largest average Ti-O-Ti angles were obtained. The samples ammonolyzed at 400 °C also showed the smallest mass loss during the thermal re-oxidation in thermogravimetric analysis (TGA). Enhanced photolumincescence brightness and an improved decay curve as well as the highest reflectance were obtained for the samples ammonolyzed at 400 °C. The improved photoluminescence and afterglow by NH 3 treatment are explained as a result of the reduced concentration of oxygen excesses with simultaneous relaxation of the lattice strain. 2670-2673 (1996). 3. B. M. J. Smets, "Phosphors based on rare-earths, a new era in fluorescent lighting," Mater. Chem. Phys. 16(3-4), 283-299 (1987 44(6), 815-818 (1982). 38. M. Stachiotti, A. Dobry, R. Migoni, and A. Bussmann-Holder, "Crossover from a displacive to an order-disorder transition in the nonlinear-polarizability model," Phys. Rev. B Condens. Matter 47(5), 2473-2479 (1993). 39. A. Bussmann-Holder, A. R. Bishop, and G. Benedek, "Quasiharmonic periodic traveling-wave solutions in anharmonic potentials," Phys. Rev. B 53(17), 11521-11530 (1996). 40. E. A. Stern, "Character of order-disorder and displacive components in barium titanate," Phys. Rev. Lett. 93(3), 037601 (2004). 41. P. Boutinaud, E. Pinel, M. Dubois, A. P. Vink, and R. Mahiou, "UV-to-red relaxation pathways in CaTiO3:Pr 3+ ," J. Lumin. 111(1-2), 69-80 (2005 ©2013 Optical Society of America

Strong Red Emissions in Pr3+‐Doped (K0.5Na0.5)NbO3–CaTiO3 Diphase Ceramics

“…Generally, Pr 3+ ‐doped CaTiO 3 shows strong red‐emitting properties with a single peak centered at about 613 nm upon UV excitation (~320 nm), which is different from green and red emissions of Pr 3+ ‐doped (K 0.5 Na 0.5 )NbO 3 host upon blue excitation (~447 nm) in our previous work . If CaTiO 3 is introduced into KNN:Pr host, which would play an important role in determining the mechanism of energy level transitions and emission properties.…”

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

“…Another possibility is that the codopant may enhance energy transfer to the fluorescence center directly, as was proposed with Bi 3+ and B 3+ codopants [6]. Additionally, several studies also show reduced strain and increased symmetry through a variety of treatments [7][8][9]. This occurs because the pristine, untreated CaTiO3 has a non-centrosymmetric distortion in the Ti octahedron that increases lattice strain [13], which can be reduced by co-doping and ammonia annealing.…”

“…This occurs because the pristine, untreated CaTiO3 has a non-centrosymmetric distortion in the Ti octahedron that increases lattice strain [13], which can be reduced by co-doping and ammonia annealing. This effect is thought to improve energy transfer to Pr 3+ luminescent centers [7] or reduced trapping centers [8,9]. It should be noted that these studies did not measure Pr oxidation state and therefore did not eliminate the possibility that a reduction of oxidized Pr 4+ is the mechanism for increased fluorescence.…”

“…Since the reporting of red luminescence in CaTiO3:Pr [4], it has been widely studied for lighting and display applications due to its ideal red emission at 610 nm [5]; however, the poor quantum efficiency limits its commercial application and has led to several further studies aimed at increasing the photoluminescence brightness. Several methods to increase luminescence have been reported: codoping with Bi 3+ in a B2O3 flux [6], the addition of SiO2 [7], Zr 4+ substitution [8], ammonia treatment [9], and codoping with Nb 5+ [10]. While each of these reports an enhancement in brightness, none provide a clear mechanism for this improved light yield.…”

Luminescence Properties of Dual‐Emission (UV/Visible) Long Afterglow Phosphor SrZrO3: Pr3+

“…Luminescent materials have been widely used in various fields for decades especially in white light‐emitting diodes (W‐LEDs) which rely on a combination of phosphors . Due to the advantages of energy saving, environment protection, long lifetime, and reliability beyond those of traditional artificial lightings, considerable efforts have been devoted to the development of some new phosphors with more excellent luminescent proprieties and chemical stability . Currently, some phosphors have been put into market for commercial use.…”