Luminescence from Bi^2+-activated alkali earth borophosphates for white LEDs

Abstract

Bi(2+)-doped MBPO(5) (M = Ba(2+), Sr(2+), Ca(2+)), synthesized in air via solid state reaction, are considered as novel orange and red phosphors for white light emitting diodes with improved colour quality. Absorption of Bi(2+) due to (2)P(1/2)-->(2)S(1/2) and (2)P(1/2)-->(2)P(3/2) could be observed and quantified. Excitation to (2)P(3/2) is accompanied by vibronic sidebands, and corresponding emission behaviour is found. The electron-phonon coupling strength increases in the order M = Ba(2+)-->Sr(2+)-->Ca(2+). In the case of MBPO(5):Bi(2+), one-, two- and even three-phonon sidebands could clearly be observed. The crystal structure of all three compounds belongs to space group P3(1)21. Bi(2+) is incorporated on M(2+) sites, and reduction of Bi(3+) to Bi(2+) occurs for reasons of charge compensation. In accordance with crystallographic data, fluorescence decay behaviour indicates that only one type of Bi(2+)-emission centers is present.

Luminescence from bismuth-germanate glasses and its manipulation through oxidants

“…5(a)). This corresponds-well to common expectations, where the lifetime 400 450 500 550 600 650 700 [9], or ~20-25 µs in crystalline alkaline earth phosphates [7]. For NIR emission, the lifetime measurement yields values of 6.8 and 27.4 µs for τ 1,2 , respectively.…”

“…In principle, a large number of species is possible, ranging from Bi 3+ as the predominant species in common applications to lower redox states such as Bi + and Bi 2+ [2,[7][8][9], or higher oxidized species such as Bi 5+ [10]. In addition, various subvalent species and ion clusters [11][12][13], Bi 0 or metallic bismuth particles have been reported.…”

Selecting Conversion Phosphors for White Light-Emitting Diodes

“…Bi 3+ has however been studied to some extent as sensitizer ion, especially in combination with Eu 3+ [105]. Recently some reports were published on borophosphates and borates activated with Bi 2+ , having a 6s 2 6p electronic ground state configuration [125,126]. Several excitation paths in the near-UV or blue are available, although they are parity-forbidden.…”

Inorganic Phosphor Materials for Lighting

“…A different approach was used by Peng et al [146] who proposed the borophosphate materials MBPO 5 (M = Ba, Sr, Ca) doped with the Bi 2? ion as novel orange and red phosphors for pcLEDs.…”