A far-red-emitting NaMgLaTeO6:Mn4+ phosphor with perovskite structure for indoor plant growth. (March 2019)

• Record Type: Journal Article
• Authors: Li, Kai; Lian, Hongzhou; Van Deun, Rik; Brik, Mikhail G.
• Is Part Of: Dyes and pigments. Volume 162(2019)
• Page Start: 214
• Page End: 221
• Publication Date: 2019-03
• Subjects: Mn4+ -- Far red luminescence -- LED -- Phosphors -- Tellurate; Dyes and dyeing -- Periodicals; Pigments -- Periodicals; 667.2
• DOI: 10.1016/j.dyepig.2018.09.084
• Languages: English
• ISSNs: 0143-7208

Abstract

Abstract: In this article, we report a far-red-emitting phosphor NaMgLaTeO6 :Mn 4+ with the perovskite structure synthesized by a high-temperature solid-state reaction method. The XRD patterns for NaMgLaTeO6 :Mn 4+ and the refinement for the representative NaMgLaTeO6 :0.006Mn 4+ confirm the purity of the as-prepared samples. The emission spectrum of optimal NaMgLaTeO6 :0.02Mn 4+ covers a series of narrow lines in the range from 16667 to 12500 cm −1 (600–800 nm), peaking at 14225 cm −1 (703 nm) due to the Mn 4+ spin- and parity-forbidden 2 Eg → 4 A2g transition. The excitation spectrum monitored at 703 nm has a broad excitation band with the range from 40000 to 16667 cm −1 (250–600 nm) centered at 28571 (350 nm) and 21505 cm −1 (465 nm), which matches well with UV or blue chips, respectively. The band can be decomposed into four Gaussian bands centered at 31646 cm −1 (316 nm), 28169 cm −1 (355 nm), 24631 cm −1 (406 nm) and 20921 cm −1 (478 nm), corresponding to the O 2- -Mn 4+ charge-transfer and the Mn 4+ 4 T1g ← 4 A2g, 2 T2g ← 4 A2g and 4 T2g ← 4 A2g transitions, respectively. The optimal concentration x of Mn 4+ in NaMgLaTeO6 :xMn 4+ was examined to be 0.02 with a corresponding quantum yield of 57.43% under 365 nm excitation, beyond which concentration quenching occurred. The energy transfer mechanism between Mn 4+ ions was determined to be a dipole-dipole interaction by analyzing the relationship between concentration and emission intensity. The temperature-dependent luminescence intensity decreased to about 75% at 150 °C of its original value at room temperature, illustrating its thermal luminescence stability of this phosphor. Moreover, a crystal field analysis for the NaMgLaTeO6 :0.02Mn 4+ representative was conducted. By using the decay lifetimes and time-resolved emission spectra, we discriminated the different occupancies of Mn 4+ not only at the Te 6+ but also at the Mg 2+ sites in the crystal structure. More importantly, the emission band matched well with the absorption band of phytochrome Pfr, which implies the phosphors can be potentially applied in light-emitting diodes (LEDs) for regulating the growth of plants. Highlights: A far-red-emitting phosphor NaMgLaTeO6 :Mn 4+ applied in plant growth LEDs was prepared. The materials can be efficiently excited by UV or blue lights, matching well with commercial LED chips. The phosphor showed good luminescence thermal stability and relative high quantum yield. The site occupancy of Mn 4+ ions for Mg 2+ and Te 6+ was analyzed by time-resolved emission spectra.