Recently, I noticed that most devices that produce X-rays are somewhat 'crude'. It is usual for these devices to either heat something up to the point where the bremsstrahlung is in the X-ray region - for example implosion backlighters in big laser facilities.
Another more commercial method is using cathode ray tubes - accelerating an electron to a high energy and then decelerating it quickly to produce X-rays.
Are there no solid-state devices as 'elegant' as LEDs to produce x-rays? Is there a strict physical limitation why these cannot be produced?