Photoluminescence Properties of Mn⁴⁺-activated Perovskite-type Titanates, La₂MTiO₆:Mn⁴⁺(M = Mg and Zn)

Abstract

). LMT and LZT substituted with 01 atom % of Mn with respect to Ti were synthesized by a polymerizable complex (PC) method.13 Titanium tetrabutoxide and nitrates of La, Mg, Zn, and Mn were used as raw materials. Citric acid and propylene glycol were also used as chelating and esterification reagents, respectively. The obtained precursors were fired at 1773 K for LMT:Mn 4+ , and at 1573 K for LZT:Mn 4+ for 2 h in air.SrTiO 3 :Mn 4+ (0.2 atom %) was also synthesized by the PC method for comparison. The obtained samples were characterized by X-ray diffraction analysis (XRD, Bruker AXS; D2 Phaser), diffuse reflectance spectroscopy in an ultraviolet visible region (UVvis DRS, Shimadzu; UV-3100) and PL spectroscopy at room temperature (Hitachi; F-4500 and JASCO; FP-6500). PL spectra at low temperature (10300 K) were also taken using a fluorescence spectrometer (Horiba; FluoroLog-3) with a cryostat. Excitation spectra were monitored for emission at 710 nm, whereas the emission spectra for LMT:Mn 4+ and LZT:Mn 4+ were taken with excitation at 340 and 360 nm, respectively. The band structures were determined by a density functional theory (DFT) using a CASTEP program.The XRD patterns indicated that the samples were obtained in a pure LMT or LZT phase with ordered B-site ( Figure S1). 14,15 No obvious changes in the peak intensity ratio and peak positions were seen with the substitution of Mn 4+ because the quantities of Mn 4+ substituted were very small (x = 0 1 atom %). When LZT was fired at 1673 K and higher temperature, La 2 TiO 5 of an impurity phase was formed accompanying with the volatilization of the Zn component. Therefore, the optimized firing temperature for LZT was 1573 K.

Photoluminescence Properties of Layered Perovskite-Type Strontium Scandium Oxyfluoride Activated With Mn4+

“…Relative position of Mn 3d orbitals to the valence and conduction bands of host materials is an important factor for Mn 4+ -activated phosphors as we have reported previously (Takeda et al, 2015, 2017). Therefore, band structures of Sr 2 TiO 4 :Mn and Sr 2 ScO 3 F:Mn were investigated by the DFT method.…”

“…Sr 2 ScO 3 F:Mn showed deep-red emission owing to transition of Mn 4+ giving a peak at 697 nm. Obvious two excitation bands in 300–460 nm and in 480–580 nm are attributed to spin-allow 4 A 2g → 4 T 1g and 4 A 2g → 4 T 2g transition of Mn 4+ ions, respectively, while a weak excitation band owing to spin-forbidden 4 A 2g → 2 T 2g transition is difficult to distinguish and it may be embedded in the tail of the 4 A 2g → 4 T 1g band as observed in other titanates and tantalates (Sasaki et al, 2014; Wang et al, 2014; Takeda et al, 2015, 2017). Interestingly, the emission from Sr 2 ScO 3 F:Mn was much stronger than that from Sr 2 TiO 4 :Mn; the internal and external quantum yields of Sr 2 ScO 3 F:Mn excited at 345 nm at room temperature (50.5 and 43.5%) were much higher than those of Sr 2 TiO 4 :Mn excited at 380 nm (3.4 and 2.5%).…”

“…Therefore, development of alternative yellow—to red-emitting phosphors activated with Eu 2+ , which can be synthesized milder conditions in comparison with nitrides, is also conducted for oxides, phosphates, and oxyhalides (Toda et al, 2006; Daicho et al, 2012, 2018; Kim et al, 2013; Sato et al, 2014; Wen et al, 2016). Besides, phosphors activated with Mn 4+ have been recently paid attention due to capability of red emission using wide variety of host materials (Srivastava and Beers, 1996; Seki et al, 2013; Ye et al, 2013; Sasaki et al, 2014; Wang et al, 2014; Takeda et al, 2015, 2017; Zhou et al, 2016; Cai et al, 2017; Wu et al, 2017; Xi et al, 2017; Zhang et al, 2017; Adachi, 2018; Jansen et al, 2018). Octahedral 6-fold coordination sites are preferred for substitution of Mn 4+ ions.…”

“…Fluorides and aluminates are paid much attention as hosts of Mn 4+ -activated phosphors from the viewpoints of their insulating nature and octahedral sites. Besides, titanates having semiconducting nature are also available for hosts of Mn 4+ -activated phosphors (Srivastava and Beers, 1996; Seki et al, 2013; Ye et al, 2013; Sasaki et al, 2014; Takeda et al, 2015; Zhang et al, 2017). We have recently reported that double perovskite-type titanates La 2 MTiO 6 (M: Mg and Zn) are available as host materials of Mn 4+ -activated phosphors although a representative perovskite-type titanate SrTiO 3 doped with Mn 4+ could not show any luminescence at room temperature due to significant thermal quenching at low temperature, ~100 K (Takeda et al, 2015).…”

“…Besides, titanates having semiconducting nature are also available for hosts of Mn 4+ -activated phosphors (Srivastava and Beers, 1996; Seki et al, 2013; Ye et al, 2013; Sasaki et al, 2014; Takeda et al, 2015; Zhang et al, 2017). We have recently reported that double perovskite-type titanates La 2 MTiO 6 (M: Mg and Zn) are available as host materials of Mn 4+ -activated phosphors although a representative perovskite-type titanate SrTiO 3 doped with Mn 4+ could not show any luminescence at room temperature due to significant thermal quenching at low temperature, ~100 K (Takeda et al, 2015). Low temperature photoluminescence measurements and theoretical band structure calculations have revealed the importance of relative position of Mn 3d orbitals to valence and conduction bands of host materials in order to avoid electron transfer from the valence band to empty t 2g orbital of Mn and photoionization.…”