Investigation of lead-free direct bandgap Ca<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si13.svg" display="inline" id="d1e887"><mml:msub><mml:mrow/><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:math>MAsO<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si14.svg" display="inline" id="d1e895"><mml:msub><mml:mrow/><mml:mrow><mml:mn>6</mml:mn></mml:mrow></mml:msub></mml:math> (M=Ga, In) double perovskites for optoelectronic and thermoelectric applications: A first principles study