Hopefully someone else has had better luck than I have had and can prove me wrong. But I have never had anything that works good for glow in the dark unless it was exposed to light prior to being in the dark. I think the best bet is high visibility paint, or high visibility paint that also glows in the dark, or even a combo. Personally I go with high visibility orange with some glow in the dark white paint (look at gun sight paint for starters) and do stripes with it over the orange. And maybe a protective clear layer on it so the paint doesn't wear off. This way it should be easier to spot and if you don't spot it but still hit it with your light hopefully you charge the paint so it glows.
No background in this, the closest thing I have is running a haunted house in the community for around 7-8 years. Drawing from that experience and working with a lot of neon paint and black lights I remember that a lot of the more high visibility colors we used such as orange, yellow, certain greens, white (especially when put on top of other colors) will stand out greatly with or without light. I recommended the high visibility orange + white glow in the dark on top as it stands out even during the day in bright light. Where as the yellow + white will tend to blend into each other more. And part of what you want is for there to be something to draw your attention to the knife, something out of place so you instinctively look at it and something orange with stripes will probably do the trick and not fit in anywhere.