The quantization of energy states resulting from wave equations under spatial confinement or boundary conditions is a foundational principle of quantum mechanics that requires no citation.
The claim states a fundamental, textbook tenet of quantum mechanics: that wave equations (like the Schrödinger equation) combined with spatial confinement or boundary conditions naturally yield quantized energy levels. This is a baseline physical principle taught in introductory physics and chemistry, making it common knowledge where specific citations are unnecessary.