title: Unusual Concentration Induced Antithermal Quenching of the Bi(2+) Emission from Sr2P2O7:Bi(2.).
abstract: The resistance of a luminescent material to thermal quenching is essential for the application in high power LEDs. Usually, thermal luminescence quenching becomes more and more serious as the activator concentration increases. Conversely, we found here that a red phosphor Sr2P2O7:Bi(2+) is one of the exceptions to this as we studied the luminescence properties at low (10-300 K) and high (300-500 K) temperatures. As Bi(2+) ions are incorporated into Sr2P2O7, they exhibit the emissions at ∼660 and ∼698 nm at room temperature and are encoded, hereafter, as Bi(1) and Bi(2) due to the substitutions for two different crystallographic sites Sr(1) and Sr(2), respectively, in the compound. However, they will not substitute for these sites equally. At lower dopant concentration, they will occupy preferentially Sr(2) sites partially due to size match. As the concentration increases, more Bi(2+) ions start to occupy the Sr(1) sites. This can be verified by the distinct changes of emission intensity ratio of Bi(2) to Bi(1). As environment temperature increases, the thermal quenching happens, but it can be suppressed by the Bi(2+) concentration increase. This becomes even more pronounced in Bi(2+) heavily doped sample as we decompose the broad emission band into separated Bi(1) and Bi(2) Gaussian peaks. For the sample, the Bi(1) emission at ∼660 nm even shows antithermal-quenching particularly at higher temperatures. This phenomenon is accompanied by the blue shift of the overall emission band and almost no changes of lifetimes. A mechanism is proposed due to volume expansion of the unit cell, the increase of Bi(1) content, and temperature dependent energy transfer between Bi(2) and Bi(1). This work helps us better understand the complex luminescent behavior of Bi(2+) doped materials, and it will be helpful to design in the future the heavily doped phosphor for WLEDs with even better resistance to thermal quenching.
authors.affiliation: †The China-Germany Research Center for Photonic Materials and Devices, The State Key Laboratory of Luminescent Materials and Devices, and Guangdong Provincial Key Laboratory of Fiber Laser Materials and Applied Techniques, School of Materials Science and Engineering, South China University of Technology, Guangzhou 510641, China.
authors.forename: Liyi
authors.initials: L
authors.lastname: Li
authors.affiliation: †The China-Germany Research Center for Photonic Materials and Devices, The State Key Laboratory of Luminescent Materials and Devices, and Guangdong Provincial Key Laboratory of Fiber Laser Materials and Applied Techniques, School of Materials Science and Engineering, South China University of Technology, Guangzhou 510641, China.
authors.forename: Mingying
authors.initials: M
authors.lastname: Peng
authors.affiliation: ‡IRCP Chimie ParisTech, 11 rue Pierre et Marie Curie, 75231 Paris Cedex 05, France.
authors.forename: Bruno
authors.initials: B
authors.lastname: Viana
authors.affiliation: §State Key Laboratory of Optoelectronic Materials and Technologies, School of Chemistry and Chemical Engineering, SunYat-Sen University, Guangzhou 510275, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Wang
authors.affiliation: ∥The College of Materials and Energy, South China Agricultural University, Guangzhou 510640, China.
authors.forename: Bingfu
authors.initials: B
authors.lastname: Lei
authors.affiliation: ∥The College of Materials and Energy, South China Agricultural University, Guangzhou 510640, China.
authors.forename: Yingliang
authors.initials: Y
authors.lastname: Liu
authors.affiliation: †The China-Germany Research Center for Photonic Materials and Devices, The State Key Laboratory of Luminescent Materials and Devices, and Guangdong Provincial Key Laboratory of Fiber Laser Materials and Applied Techniques, School of Materials Science and Engineering, South China University of Technology, Guangzhou 510641, China.
authors.forename: Qinyuan
authors.initials: Q
authors.lastname: Zhang
authors.affiliation: †The China-Germany Research Center for Photonic Materials and Devices, The State Key Laboratory of Luminescent Materials and Devices, and Guangdong Provincial Key Laboratory of Fiber Laser Materials and Applied Techniques, School of Materials Science and Engineering, South China University of Technology, Guangzhou 510641, China.
authors.forename: Jianrong
authors.initials: J
authors.lastname: Qiu