AJAX调用从json_encode返回空对象

I'm making an AJAX call to a fairly simple PHP function. The response should be a JSON object to be manipulated, but my response is always an empty object.

Relevant Code:

index.html's AJAX Call:

$( function() {
    $('#dates').on('submit', function (e) {
        var start_time = new Date().getTime();
        e.preventDefault();
        var submitData = $('#dates').serialize();
        console.log(submitData);
        $.ajax({
            type:'POST',
            url:'inflow.php',
            data:$('#dates').serialize(),
            dataType: 'json',
            beforeSend: function(){
                $('#loading').show();
            },
            success: function(data) {
                console.log(data);
                $('#loading').hide();
            },
            error:function(xhr, desc, err){
                alert('You tried to send an AJAX request, but something went wrong.
 Please Contact the NASR WebDev Team');
                console.log(xhr);
                console.log("Details: " + desc +"
Error: "+ err);
            }
        });
    });
});

inflow.php's array creation and echo:

<?php

$msqlStart = $_POST['start_date'];
$msqlEnd = $_POST['end_date'];

$inflowQuery=
    "SELECT
        COUNT,
        QUEUE_ID,
        QUEUE_GROUP,
        INFLOW_DATE,
        LINE_OF_BUSINESS
    FROM
        ticket_inflow.inflow
    WHERE
        ROUTE_STATUS = 'Inflow'
        AND inflow_date between ? and ?";

    $connect = new mysqli($host, $user, $password, $database);
    if ($connect->connect_error){
        die("Failed to Connect:.".$connect->connect_errno.": ".$connect->connect_error);
    }
    if(!($statment = $connect->prepare($inflowQuery))){
        die('Error in Preparation Error Number:%d Error: %s');
    }
    if(!$statment->bind_param('ss', $msqlStart, $msqlEnd)){
        die ('Error in Binding');
    }
    if(!$statment->execute()){
        die('Error In Execution');
    }
    $statment->bind_result($inflowCount, $inflowQueue, $inflowQG, $inflowDate, $inflowLOB);

    $a_json = array();
    $jsonRow = array();

    While($statment->fetch()){
        $UID = 0;
        $jsonRow['UID'] = $UID++;
        $jsonRow['count'] = utf8_encode($inflowCount);
        $jsonRow['inflow_date'] = utf8_encode($inflowDate);
        $jsonRow['queue'] = utf8_encode($inflowQueue);
        $jsonRow['queue_group'] = utf8_encode($inflowQG);
        $jsonRow['lob'] = utf8_encode($inflowLOB);
        array_push($a_json, $jsonRow);
    }


    $jsonReturn = json_encode($a_json);

    echo $jsonReturn; 

?>

If I go directly to inflow.php and pass it parameter's identical to what the page passes it, I get what appears to be a nice JSON object, however when I look at the response Chrome Developer's Tools I get:

[]

And nothing more.

You are sending form data, not json;

$.ajax({
        type:'POST',
        url:'inflow.php',
        data:$('#dates').serialize(),
        //contentType: "application/json",<-- remove this
        dataType: 'json',