Color tunable Ba0.79Al10.9O17.14:xEu phosphor prepared in air via valence state control

Abstract

A series of luminescent Ba 0.79 Al 10.9 O 17.14 :xEu (x = 0.005-0.12) phosphors were prepared by high-temperature solid-state reaction in air atmosphere. The coexistence of Eu 2+ and Eu 3+ was observed and verified by photoluminescence (PL) and photoluminescence excitation (PLE) spectra, X-ray photoelectron spectra (XPS), and diffuse reflection spectra. The band emission peaking at 430 nm was assigned to 4F 6 5D-4F 7 transition of Eu 2+ , and another four emissions peaking at 589, 619, 655, and 704 nm were attributed to 4F-4F transitions of 5 D 0 -7 F J (J = 1, 2, 3, 4) of Eu 3+ . The related mechanism of self-reduction was discussed in detail. The color of the Ba 0.79 Al 10.9 O 17.14 :xEu phosphors could be shifted from blue (0.23, 0.10) to red (0.42, 0.27) by doping Li + ions, and the temperature dependence properties were investigated.

Tetrahedrally coordinated rigid crystal structure enables partial self-reduction of mixed-valence europium for optical thermometric application

“…33,65 Two Eu 3+ ions heterovalently doped at two Ca 2+ sites create a charge negative vacancy, V′′ Ca (Kröger–Vink notation), near the Eu 3+ ion to maintain charge neutrality. The negative charges in the V′′ Ca vacancy will thermally transmit to the Eu 3+ ion, thus reducing the Eu 3+ to Eu 2+ as suggested by the following expressions: 42,48,66 …”

“…37 For example, through slightly decreasing Si stoichiometry in Ca 2 Al 2 Si 1−x O 7 (x = 0-0.04), Hu et al 38 to Eu 2+ could also take place even when prepared in the oxidizing atmosphere with O 2 . [40][41][42][43][44]49 These behaviors are due to Eu 2+ ions having relatively high stability in some special structures and the low reduction potential (Eu 2+ /Eu 3+ = 0.35 V). 45,46 It was proposed by Su et al 43 that the necessary conditions determining whether self-reduction occurs in the oxidizing atmosphere are: (a) the compounds having an appropriate structure with the tetrahedral anion groups (BO 4 , SO 4 , PO 4 , SiO 4 , or AlO 4 ) with no oxidizing ions; (b) the divalent cation of the host being replaced by Eu 3+ ions and the substituted cation possessing a similar radius as the Eu 2+ ions.…”

Self-reduction-induced BaMgP2O7:Eu2+/3+: a multi-stimuli-responsive phosphor for X-ray detection, anti-counterfeiting and optical thermometry

“…Another prevalent approach is through non-equivalent substitution in a rigid three-dimensional framework structure, where partial self-reduction of Eu 3+ → Eu 2+ in air is realized according to the defect charge compensation principle. [24][25][26][27] In this case, Eu 3+ enters a mono-or di-valent cationic site, which is involved in a network composed of SiO 4 , AlO 4 , BO 4 , PO 4 , or other groups. The network in these lattices is not that compact as described by Su 28 so that the self-reduction from Eu 3+ to Eu 2+ is not complete and the luminescence intensity ratio of Eu 2+ /Eu 3+ can be controlled by the reaction temperature and Eu content.…”

“…The network in these lattices is not that compact as described by Su 28 so that the self-reduction from Eu 3+ to Eu 2+ is not complete and the luminescence intensity ratio of Eu 2+ /Eu 3+ can be controlled by the reaction temperature and Eu content. For instance, self-reduction phenomena and defect reaction mechanisms were reported in CsAlSi 2 O 6 :Eu 3+ / Eu 2+ , 29 Ba 0.79 Al 10.9 O 17.14 :Eu 3+ /Eu 2+ , 25 and CaZr(PO 4 ) 2 :Eu 3+ / Eu 2+ . 30 The third approach takes advantage of the native feature of a rigid framework crystal structure, which facilitates a steady control of the Eu 2+ /Eu 3+ ratio and reproduciblesynthesis.…”

Luminescence properties and energy transfer behavior of colour-tunable white-emitting Sr4Al14O25 phosphors with co-doping of Eu2+, Eu3+ and Mn4+

“…With the ever-increasing demands of humankind for illumination quality, white light-emitting diodes (WLEDs) are replacing the incandescent and uorescent lamps gradually and becoming a new generation of solid state lighting sources for buildings and scenery lighting, LCD backlighting, interior lighting, automobiles, agriculture, medicine and aerospace. [1][2][3][4] At present, the commercial method to generate white light emission is exciting the yellow-emitting Y 3 Al 5 O 12 :Ce 3+ (YAG:Ce 3+ ) with an InGaN light-emitting diode (LED) chip which emits blue light with the wavelength between 450 nm and 480 nm typically. 5,6 Because of the emission deciency in the red region, this WLED shows poor colour rendering and appears a simple cool white.…”