A more 5e friendly way to phrase it might be
Before you take the attack action, you may spend 1 ki point. If you do, your unarmed strikes deal 1d6 damage until the end of your turn, this increases to 1d8 at 5th level and 1d10 at 11th level
However, you didn't specify if you want it to continue upping the die, so you could add
...and 1d12 at 17th
Balance-wise, you could change it too
...1d6 damage until the end of your next turn.."
Mechanically, this proposed revision is weak.
The difference from a d4 to a d6, d6 to d8, etc is an average of 1 damage. Monks are not traditionally designed for DPS and often run out of ki. If we look at comparable options, flurry of blows functionally gives an additional attack that does 4 damage minimum at 2nd level assuming a 16/17 dex and increases from there. If you use the ability and hit you will deal an extra 1 damage per unarmed strike, assuming you aren't using a weapon and only use unarmed strikes and every attack hits, you will deal an extra 3 damage.
If you are looking for a real burst of extra damage, you could flurry of blows AND use this ability for an extra 4 damage if everything hits. There is no harm in adding it as an additional ability however this definitely could do a lot more.
Potential options could be any number of these, declaring the ability like a smite after you hit, having it last until your next turn, potentially having it last for 1 minute, giving a bonus to hit, or just additional damage.