Albert Einstein (1905) used Planck's relationship to explain the results of the photoelectric effect which showed that the energy E of ejected electrons was dependent upon the frequency f of incident light as described in the equation E=hf. It is ironic that in 1921 Albert Einstein was awarded the Nobel Prize for this discovery, though he never believed in particles and acknowledged that he did not know the cause of the discrete energy transfers (photons) which were contradictory to his continuous field theory of matter!
In 1954 Albert Einstein wrote to his friend Michael Besso expressing his frustration;

All these fifty years of conscious brooding have brought me no nearer to the answer to the question, 'What are light quanta?' Nowadays every Tom, Dick and Harry thinks he knows it, but he is mistaken. (Albert Einstein, 1954)

Most importantly, Albert Einstein also suspected that Matter could not be described by a continuous spherical force field;

I consider it quite possible that physics cannot be based on the field concept, i.e., on continuous structures. In that case, nothing remains of my entire castle in the air, gravitation theory included, [and of] the rest of modern physics. (Albert Einstein, 1954)

Albert Einstein's suspicions were well justified, for he had spent a lifetime trying (and failing) to create a unified field theory of matter that explained both Quantum Theory / Light and Relativity / Gravity.
In fact Matter, as a Spherical Standing Wave which causes the 'Field' effect, interacts with other matter in discrete standing wave patterns, not with continuous force fields as he had imagined, thus his task was ultimately impossible, as he sadly came to realise towards the end of his life.

However, his work on the photoelectric effect confirmed that light energy was only emitted and absorbed by electrons in discrete amounts or quanta. This quanta of light energy soon became known as the 'photon' (i.e. discrete like a particle) and led to the paradox that light behaved both as a continuous e-m wave (Maxwell, Albert Einstein) as well as a discrete particle/photon (Planck, Albert Einstein). So we see that Albert Einstein was partly responsible for the discovery of the particle/photon concept of light, though he completely rejected the notion of discrete particles. He writes;

Since the theory of general relativity implies the representation of physical reality by a continuous field, the concept of particles or material points cannot play a fundamental part, nor can the concept of motion. (Albert Einstein)

Albert Einstein is correct that there are no discrete particles, and that the particle can only appear as a limited region in space in which the field strength or the energy density are particularly high. But it is the high Wave-Amplitude of the Wave-Center of a Spherical Standing Wave in Space (not of a continuous spherical force field) that causes the particle effect. Thus of three concepts, particles, force fields, and motion, it finally turns out that Motion, as the spherical wave motion of space, is the correct concept, as it then explains both particles and fields. (For further explanation see Article on Relativity)
It is most important to realise though that Albert Einstein was correct in imagining matter as being spatially extended, as he explains;

I wished to show that space time is not necessarily something to which one can ascribe to a separate existence, independently of the actual objects of physical reality. Physical objects are not in space, but these objects are spatially extended. In this way the concept empty space loses its meaning. (Albert Einstein)

It is certainly true that the particle and its forces / fields are very useful mathematical concepts, unfortunately, they also cause many problems and paradoxes because they are approximations to reality and do not physically exist.

We can now finally solve these problems by understanding the reason for these discrete energy states, which are due to the fact that standing waves only exist at discrete frequencies, like notes on the string of a guitar, thus while the Spherical Standing Wave Structure of Matter predicts that energy exchanges will be discrete, as observed, the continuous e-m wave does not anticipate this.
Thus the Spherical Standing Wave Structure of Matter explains Max Planck's (1900) discovery that there are only certain allowed discrete energy states for electrons in molecules and atoms, and further, that light is only ever emitted and absorbed by electrons in discrete or 'quantum' amounts, as the electrons move from one stable standing wave pattern to another. (This is explained in more detail in section 1.4)Quantum-Physics