[RPG] Spell casting phrases to improve roleplaying

With the release of Mordenkainen's Tome of Foes, there is a list on page 73 of dwarven deities and their domains. Berronar Truesilver and Tharmekhûl both have the Light domain. I'll leave my original answer below the break for reference in case future readers wouldn't prefer the two deities listed above.

Dugmaren Brightmantle seems like a good candidate. From the Wikipedia page:

Dugmaren Brightmantle is the dwarf deity of scholarship, discovery, and invention. Dugmaren shares the Dwarven Mountain on the Outlands with Dumathoin and Vergadain. Dugmaren appears as an elderly dwarf with sparkling blue eyes.

His domain isn't strictly light, but those domains are probably more of a suggestion. It could be argued that Light would be a fitting domain for this deity. Discovery, knowledge, and enlightenment go hand-in-hand with light in certain deity systems. Alternatively, Marthammor Duin could be an option since that deity has an affinity for lightning.

Tharmekhûl could be an option as well due to being associated with fire and the light domain has quite a few fire spells.

Source: Dwarf Deities on Wikipedia

The PHB (pg 198) has that section written as such:

Most DMs have a monster die the instant it drops to 0 hit points, rather than having it fall unconscious and make death saving throws.

Mighty villains and special nonplayer characters are common exceptions; the DM might have them fall unconscious and follow the same rules as player characters.

Note the use of most and common exceptions.

Additionally, PHB 197 has the following:

The best way to save a creature with 0 hit points is to heal it. If healing is unavailable, the creature can at least be stabilized so that it isn’t killed by a failed death saving throw.

You can use your action to administer first aid to an unconscious creature and attempt to stabilize it, which requires a successful DC 10 Wisdom (Medicine) check.

Note the use of creature here, not you or player character.

That makes it clear that having an enemy die instantly at 0 is an option that the DM may use. It's completely legal to rule that monsters use the same rules "Dropping to 0 Hit Points" as PCs. If you want to make sure that some of your enemies are alive after the battle to interrogate them, you should:

• Make use of the "Knockout" rule, when able.
• Otherwise, ask your GM to determine which enemies are still alive; (s)he can determine that by fiat, or by rolling death saving throws for each of the enemies.
• At this point, you should know which enemies are alive but dieing, and which are at 0, but stable, and you can move on from there.