How to use Background image in a Materialize column

Good morning, my question is how I should do to put a background image in a materialize column.

For example, suppose I want a section with half an image and half a text would be something like that?

<div class="row">
        <div class="col m6 imagen-aqui">

        </div>

        <div class="col m6">

        </div>
</div>

Then in the CSS I do something like that

.imagen-aqui {

background-image: url('url o imagen');
background-repeat: no-repeat;
background-size: cover;

}

But nothing appears :( what am I doing wrong? or do you know in some other way to separate a large image with text and titles on one side

Thanks in advance