Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: White Organic Light-Emitting Diodes with fine chromaticity tuning via
  ultrathin layer position shifting   Non-doped white organic light-emitting diodes using an ultrathin
yellow-emitting layer of rubrene (5,6,11,12-tetraphenylnaphtacene) inserted on
either side of the interface between a hole-transporting NPB
(4,4'-bis[N-(1-naphtyl)-N-phenylamino]biphenyl) layer and a blue-emitting DPVBi
(4,4'-bis(2,2'-diphenylvinyl)-1,1'-biphenyl) layer are described. Both the
thickness and the position of the rubrene layer allow fine chromaticity tuning
from deep-blue to pure-yellow via bright-white with CIE coordinates (x= 0.33,
y= 0.32), a external quantum efficiency of 1.9%, and a color rendering index of
70. Such a structure also provides an accurate sensing tool to measure the
exciton diffusion length in both DPVBi and NPB (8.7 and 4.9 nm respectively).

31
The categories of this paper are: ao-sci
20
The categories of this paper are: acc-phys
18
The categories of this paper are: econ
32
The categories of this paper are: atom-ph
15
The categories of this paper are: nucl-ex
4
The categories of this paper are: cond-mat
23
The categories of this paper are: solv-int
5
The categories of this paper are: gr-qc
22
The categories of this paper are: chao-dyn
34
The categories of this paper are: chem-ph
17
The categories of this paper are: q-fin
35
The categories of this paper are: mtrl-th
19
The categories of this paper are: eess
33
The categories of this paper are: plasm-ph
6
The categories of this paper are: astro-ph
30
The categories of this paper are: q-alg