A breakthrough in rare earth display technology could increase the resolution of smartphone screens by a factor of over a million; but consumers will need to open their eyes widely, and their wallets, to see the difference.

By putting six different types of rare earth elements in a nanoscale capsule and beaming lasers onto it, Chinese researchers obtained for the first time the full spectrum of visible light, according to a paper published in the journalAngewandte Chemie.

Apple's top of the range retina displays – used in iPhones, iPads and Macbooks – currently boast around 300 pixels per square inch (PPI). By comparison, the rare earth display could reach 850 million PPI.

The study opens up a new direction for the future development of display technology utilising rare earth materials, according to Zhang Zhongping, a professor at the Chinese Academy of Sciences' Hefei Institute of Physical Science and lead author of the study.

But it could take a long time before the displays are seen by consumers, he said.

"Pixels are only one part of display technology. When pixels go down in size, it requires laser beams to become extremely fine as well," Zhang said.

"To generate and control laser beams at a nanoscale [level] is a problem that has not been solved."

Pixel-wise however, the rare earth display has some significant advantages over present technologies such as plasma and light-emitting diode (LED) screens. All display devices for consumer use today generate colours by mixing red, yellow and blue.

While the three-colour approach was instrumental in the invention of colour displays, problems emerged as the resolution increased. For decades, scientists have searched for a method of displaying the full-spectrum of visible light in a single point without colour blending or filtering.

In the rare earth screen, the pixels have a ball-like structure with six layers of different elements such as Thulium and Erbium. By changing the wavelength of the laser beam, they can produce different colours.

Though there are a number of emerging technologies – such as quantum dot or nanocrystal displays – that also claim to solve this problem, their production either requires poisonous materials or is too sophisticated at present for mass production.

Rare earth displays on the other hand are simple to produce, Zhang said.

"The biggest challenge is to find the right rare earth elements and control their precise composition," he said.

"A wrong element or slight disproportion will make it impossible to obtain pure white light, which is the benchmark from which to evaluate the performance of a display technology."

The team has spent three years on the project. After many failures, they finally achieved a formula that could be mass produced in chemical plants.

The issue of price, however, remains. Though China is the world's largest rare earth producer and the price of ore has dropped in recent years, Zhang said a smartphone display using rare earth elements could be quite expensive.