The escalating energy demand coupled with limited conventional energy resources led to a widening gap between supply and demand, making it inevitable to look for novel energy efficient technologies. Solid state lighting is one of the promising areas where a significant amount of energy consumed can be conserved without compromising on the sophistications of conventional lighting. Solid state lighting kindled the interest of researchers owing to their impressive energy efficiency, longer life time, greater reliability, eco-friendly nature and the reasonable ease of fabricating the white light emitting diodes (WLEDs). Typically blue light emitting chip in combination with yellow light emitting phosphor¹, Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce³⁺) have been used to produce the white light. However, the obtained white light has poor light quality and low color rendering index (CRI >80), due to lack of red component in the obtained white light spectrum. Tricolor phosphors (red, green and blue) in combination with near ultra violet (NUV) emitting source (InGaN chip) were considered to be an alternative to get better lighting properties and the generated white light by this technique has similarity to sun light and a good CRI value^2,3. The commercially used red phosphor Y₂O₂S:Eu³⁺ is sensitive towards moisture and decomposed under high temperature which is harmful to the environment. Nitrides, CaAlSiN₃:Eu²⁺ can be used as a substitute but its preparation needs greater care and highly controlled preparation conditions. Therefore, the red phosphors with thermal, chemical stability and high luminous intensity became an essential need for lighting industries.

Recently, mullite and mullite-type ceramics have attracted attention because of their interesting optical properties⁴, high thermal and chemical stability⁵. In this context, we report Eu³⁺ activated mullite-type Bi_(1-x)2Ga₂Al₂O₉:xEu³⁺ (x = 0.00, 0.025, 0.05, 0.10, 0.20 and 0.30) solid solution which were prepared by simple solid state method. The prepared samples were characterized by x-ray diffraction and luminescence properties were measured under near UV and blue light excitation. The europium dopped Bi₂Ga₂Al₂O₉ (BGAO) showed characteristic excitation peaks between 250 nm and 500 nm. The chromaticity coordinates (0.61, 0.37) calculated under blue light excitation for 20% Eu³⁺ doped BGAO, located in orange-red region of chromaticity graph. The coordinates were close to the reference red phosphors and the results indicate that it have potential application in the field of lighting and displays under blue LED excitation.

References:

1. S. Nakamura, MRS Bull., 22, 29–35 (1997).

2. J. S. Kim et al., Appl. Phys. Lett., 85, 3696–3698 (2004).

3. C. K. Chang and T. M. Chen, Appl. Phys. Lett., 91, 081902 (2007).

4. G. Blasse and O. B. Ho, J. Lumin., 21, 165–168 (1980).

5. M. M. Murshed and T. M. Gesing, Mater. Res. Bull., 48, 3284–3291 (2013).