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Mixed alkaline earth-based, rare earth-doped nitride phosphors, (Sr,Ca)AlSiN 3 :Eu 2+ , were synthesized from metal hydride powders as raw materials under atmospheric-pressure heating conditions. The resultant phosphors were almost free from impurity phase and well crystallized by using CaH 2 as a flux. An intense red emission band peaking at about 644 nm was observed on (Sr 0.42 Ca 0.56 )AlSiN 3 :Eu 2+ and the peak position was shifted at the shorter wavelength side by increasing the Sr content than that of CaAlSiN 3 :Eu 2+ .Recently, metal nitride phosphors such as M 2 Si 5 N 8 :Eu 2+ (M = Ca,Sr,Ba) 1-4 and M'AlSiN 3 :Eu 2+ (M' = Ca,Sr) 5-7 have been practically used as a red color component source for LED solid illumination which are excited by blue lights of 9 In 2008, Watanabe and co-workers 10 have reported that SrAlSiN 3 :Eu 2+ is one of much notable phosphors to provide the emission band peaking at 610 nm which is much close to the red isochromatic region around 615 nm compared with CaAlSiN 3 :Eu 2+ (about 655 nm). However, Sr atom is a little too large to share 4a site (Cmc2 1 ) in a three-dimensional (Al 2 Si 2 N 12 ) n network consisting of AlN 4 and SiN 4 tetrahedral units, so that any host lattice of SrAlSiN 3 has not been synthesized even by the direct nitriding method using low alloy powders under mild-pressure conditions of N 2 gas below 1 MPa up to date. 10,11 Also, the other synthesis route using the Sr 2 N 0.92 powder as a Sr source, which is of strong deliquescence and high cost, is at least required the same high-pressure condition as 190 MPa and the production yield is much low (ca 1%). 12 Only by replacing Ca atom with Sr one, (Sr,Ca)AlSiN 3 :Eu 2+ phosphors have been reported to produce from the corresponding (Sr,Ca)AlSi alloy precursors in each single phase form under the high-pressure condition of N 2 gas on a hot isostatic pressing apparatus, 11-14 because the sublimation of Sr metal extremely takes place at the temperature around the boiling point (bp = 1382 • C) before such direct nitriding process for metals. Furthermore, several groups have been succeeded in synthesizing such metal nitride phosphors by applying unique techniques, e.g. ammothermal synthesis, 15 spark plasma firing, 16 and metathesis reactions 17 at low temperature. However, most of these methods also required high-pressure conditions of 0.9 to 190 MPa.Meanwhile, new direct nitriding method using metal hydrides precursors as the raw materials, Si/MSi 2 H x (M = Ca, Sr, Ba), has been proposed to produce the corresponding M 2 Si 5 N 8 :Eu 2+ phosphors with good luminescence properties, 18 because most of metals and alloys are easily pulverized by a hydrogen absorbing effect so called "hydrogen embrittlement".In this work, the (Sr,Ca)AlSiN 3 :Eu 2+ phosphors were synthesized from the mixtures of (Sr,Eu)AlSiH x powders derived from (Sr,Eu)AlSi alloys and CaH 2 powder added as a flux under atmospheric-pressure (ca. 0.1 MPa) heating conditions, where these metal hydrides were highly reactive to N 2 gas and the excess amount...

High-quality powders of mixed metal nitride phosphor, CaAlSiN 3 :Eu 2+ , were successfully synthesized using only inexpensive and air-stable materials, viz. CaCN 2 , CaCO 3 :Eu 3+ , AlN, and Si 3 N 4 , with no impurities such as AlN or carbon residue by a CRN method even under conditions of normal N 2 pressure (0.1 MPa) and a moderate temperature of 1600°C for 57 h. The resultant phosphors were well crystallized and gave an intense red emission band peaking at about 650 nm by optimizing the dopant amount of Eu 2+ ion (ca. 3 atom %).Metal nitride phosphors such as M 2 Si 5 N 8 :Eu 2+ (M = Ca, Sr, and Ba) and M¤AlSiN 3 :Eu 2+ (M¤ = Ca and Sr) have been used as key materials for high color-rendering solid illumination parts based on blue-emitting InGaN chips as the red color component source. This is because the 5d energy level for the excited state of Eu 2+ ion is effectively lowered by the nephelauxetic effect of the covalent EuN bonding, and thus the 4f electron of Eu 2+ ion is excited to the 5d energy level even by the blue light of an LED chip.

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