jquery - How to use css formatting in Full Calendar JSON string being passed from PHP page?

one text

I would like to format the title element of my calendar element, to take a new line and add the part I specify as bold. I have the following PHP page which is where I am passing the event data to the calendar which is all working ok.

 $deliveryDateArray[] = array(
            'mainID'  => $row["orderMainID"],
            'id'   => $row["orderBuildandDeliveryID"],
            'title'   => $row["lastName"] . " (" . $row["postcode"] . ") | " .  $row["productName"] . $insulation2." || ".$materials,
            'start'   => $row["deliveryDate"],
            'url'   => 'orderViewSort.php?orderID=' . $row["orderMainID"],
            'color' => $color,
            'materials' => $insulation
        );
echo json_encode($deliveryDateArray);

I have tried adding "<'b'>" and "</br" in front of it but if I do that it will just echo the full string out with the in the event name.

For reference this is how the title is getting applied to the calendar

var calendar = $('#calendar').fullCalendar({
    editable:true,
    header:{
      left:'prev,next today',
      center:'title',
      right:'month,agendaWeek',
    },
    editable: true,
    droppable: true, 
    events: 'LoadAllTeams.php'

Is there any way I can do this?

EDIT I added the "\n" which brought the page break through, but not sure how to bring the bold through for a specific part of the title string.

'title'   => $row["lastName"] . " (" . $row["postcode"] . ") | " .  $row["productName"] . $insulation2." ||\n ".$materials

Thanks.