If I may, I want to offer a suggestion for you
What I did for my gemstone renders is actually create a whole lighting studio, including lights. I started with a cube, cutting out a portion of one side to have an opening to "place" the gemstone in, as well as sticking a plane inside it to set the stones on. In addition, I added a very small amount of thickness (around 5mm or so) to the cube with the Solidify modifier, for better translucency. For the cube, I set it to glossy translucent with a light-grayish diffuse color and transmission to pure white. IOR is trivial ultimately. For that plane that is essentially a floor, I set it to a glossy material with an almost black color, the IOR set to the PET plastic preset, and roughness around 0.0010. This is basically an acrylic glass (if you wish, you could use an acrylic glass preset if it's still available in LuxCore's presets, I remember the old version had it).
For lighting, I use a combination of light emitting planes and a Hemi lamp. For my scene, I use two planes, one slightly larger than the other, and set it to Emission with a blackbody color. Daylight works best and fits the industry standard if you browse around gemstone lighting tutorials (around 5000-5500k). Scale for all of your objects is also very important - the cube is around 50cm all around, with the floor slightly smaller.
As for the gemstones, once you model one, scale it down to a realistic value for the gem you're trying to simulate. I sometimes experiment with adding a very slight bevel on top of the smaller size using the Bevel modifier. I use 4 segments usually, to simulate hard edges on an otherwise smooth stone. At this stage, do what you think works best
Feel free to take this into consideration, see what comes out of it
