You could make a directive for this.
.directive('backImg', function(){
return function(scope, element, attrs){
var url = attrs.backImg;
var content = element.find('a');
content.css({
'background-image': 'url(' + url +')',
'background-size' : 'cover'
});
};
});
<ion-item back-img="{{item.bg}}"></ion-item>